Abstract
Organic bulk heterojunction solar cells are a promising candidate for low-cost next-generation photovoltaic systems. In bulk heterojunction polymer solar cells, conjugated polymers and fullerene derivatives [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) function as the electron-donating and electron-accepting materials, respectively. In this paper, we report the photovoltaic response of the solution-processed bulk heterojunction (BHJ) solar cell based on poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): modified PCBM (MPCBM) blend. The BHJ showed power conversion efficiency (PCE) up to 1.78%. The PCE has been further improved up to 1.95% after thermal annealing of the active layer. The increase in the PCE with the thermally annealed blend is mainly attributed to the improvement in incident photon to current efficiency (IPCE) and short circuit photocurrent (Jsc).
Abbreviations: AM, air mass; BHJ, bulk heterojunction; C60, Buckminsterfullerene; D-A, donor-acceptor interface; FF, Fill factor; HOMO, highest occupied molecular orbital; IPCE, incident photon to current efficiency; ITO, indium tin oxide; Jsc, short circuit photocurrent; J-V, current density-voltage characteristic; LUMO, lowest unoccupied molecular orbital; MEH: PPV, poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene); MPCBM, modified [6,6]-phenyl-C61-butyric acid methyl ester; η, efficiency; NIR, near infrared; PCBM, [6,6]-phenyl-C61-butyric acid methyl ester; PCE, power conversion efficiency; PEDOT: PSS, poly (3,4-ethylenedioxythiophene)-block-poly(styrenesulfonate); PSCs, polymer solar cells; SEM, scanning electron microscopy; THF, tetrahydrofuran; Voc, open circuit voltage.
1 Introduction
Polymer-based organic solar cells have attracted attention as a renewable energy source due to their low cost, ease of manufacture, and compatibility with flexible substrates [1, 2]. Materials such as small organic molecules [3, 4], star-shaped oligomers [5, 6], and conjugated low-band gap polymers [7, 8] due to their inexpensive, easily processable and tailored functionality by molecular design and chemical synthesis are under extensive research worldwide. One of the important alternative followed to improve the photovoltaic efficiencies is donor-acceptor (D-A) proximity in the devices by using blends of donor-like and acceptor-like molecules or the polymers, which are called D-A bulk heterojunction solar cells [9–11]. Thus, in bulk heterojunction polymer solar cells, conjugated polymers and fullerene derivatives [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) function as the electron-donating and electron-accepting materials, respectively [12, 13]. This composite layer can be prepared as a large area in a single step by using techniques such as spin coating, inkjet printing, spray coating, gravure coating, roller casting, etc. [14]. By a simple spin coating from a solution of these homogeneous blends of conjugated polymer and fullerene derivatives, largely increased interfacial area (where charge separation occurs and recombination is reduced) can be achieved.
The main difference between the conventional or inorganic solar cells and the BHJ solar cells are the charge transport mechanism as well as their photovoltaic behavior, as in BHJ solar cell excitons are generated in the photovoltaic layers, and at the donor-acceptor interfaces, these excitons dissociates into electrons and holes.
Electroluminescent semiconducting polymers (ELSCPs) have good optoelectronic characteristics because their polymer main chains are composed of alternately conjugated double bonds and because the delocalized π electrons can move along each main chain or hop between the adjacent main chains [15]. There is a wide application of poly para-phenylenevinylene (PPV) and its derivatives in organic solar cells due to their semiconducting and luminescence properties. Thus, poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), which is a class of PPVs and a well-known luminescent polymer material having low driving voltage and high luminescent efficiency [16, 17], has been widely utilized in fluorescent sensors, electrochromic devices [18–20], polymer light-emitting diode [21], and as a donor material in the BHJ photovoltaic cells [22]. This hairy rod polymer MEH-PPV is highly soluble in common organic solvents, such as tetrahydrofuran (THF), chlorobenzene, chloroform, xylene, and toluene because its backbone is bonded with the short flexible ethereal side chains [23]. The photoactive layer of organic solar cells based on poly (2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) and [6,6]-phenyl C61 butyric acid methyl ester (MEH-PPV:PCBM), have been studied over the past years [24, 25], and many attempts for making efficient photovoltaic (PV) cells using these composite films have been published, with limited efficiency [26, 27]. In 2013, Yang et al. have synthesized a MEH-PPV:PCBM (1:4 weight ratio) BHJ device and added ditertbutyl peroxide (DTBP) as an additive and found the increase in the efficiency for the device containing 0.5 wt% DTBP was highest [28]. Jung et al. also prepared solutions of conjugated polymer MEH-PPV and PCBM in xylene (XY), O-dichlorobenzene (O-DCB), chloroform (CF), chlorobenzene (CB), toluene, and THF in the optimized 1:4 weight ratio [29].
To increase the power conversion efficiency (PCE) value, the Voc, Jsc, and FF of the device were needed to be enhanced. The Voc can be augmented by raising the lowest unoccupied molecular orbital (LUMO) level of the fullerene relative to the highest occupied molecular orbital (HOMO) level of the donor [30, 31]. The Voc of a BHJ solar cell may also be increased using electron irradiation method [32]. Ideally, the polymers should have a broad absorption area in the solar spectrum; thus, efficient light harvesting can be ensured and a high charge carriers mobility for charge transport with a suitable energy levels of polymers is required that matches those of the fullerides. The discovery of photoinduced electron transfer from a conjugated polymer as a donor to buckminsterfullerene C60 as an acceptor [9] provided a molecular approach to enhanced photovoltaic conversion.
In 2004, cell (MEH-PPV:PCBM) with 2.9% efficiency was demonstrated under 100 mWcm-2 illumination intensity [24]. Yang et al. reported a lower conversion efficiency for similar cells based on MEH-PPV and polymers with substituents containing C60 moieties [33]. Thus, to enhance the performance and/or efficiency of a BHJ photovoltaic cell, we need to make much more effort to modify the substituent of PCBM by introducing substituents on its phenyl ring [34, 35] or by replacing the phenyl ring with other groups [36, 37]. PCBM bisadduct [38] and PCBM multiadduct [39] as well as endohedral fullerenes [40] were reported as PV acceptor material in the last few years. The LUMO energy levels for these fullerene derivatives are higher, which results in higher Voc as well as higher PCE [38, 40] for P3HT-based solar cells.
Synthesis of a modified PCBM, which is soluble in THF, was reported by Mikroyannidis et al. [41]. Owing to the presence of the cyanovinylene 4-nitrophenyl segment, the modified PCBM showed stronger absorption in the visible region of solar spectrum than the PCBM. In 2013, Matsuo et al. reported that the addition of a dihydromethano group to the fullerenes improves the performance of BHJ organic solar cells [42]. Recently, the highest efficiency of 3% has been demonstrated for a MEH-PPV:MAPbI3-based BHJ like solar cell by Rizzo et al. [43]. The efficiencies obtained for different BHJ photovoltaic devices are summarized in Table 1.
The efficiencies obtained for different BHJ photovoltaic devices.
| S. no. | Device | Voc (V) | Jsc (mAcm-2) | FF | PCE (η%) | References |
|---|---|---|---|---|---|---|
| 1 | P3HT/bisPC60BM | 0.724 | 9.14 | 0.68 | 4.5 | [38] |
| 2 | P3HT/PC60BM | 0.61 | 8.94 | 0.60 | 2.4 | [39] |
| 3 | BDT-based low band gap polymer PBDTTT-E | 0.62 | 13.2 | 0.63 | 5.15 | [44] |
| 4 | BDT-based low band gap polymer PBDTTT-C | 0.70 | 14.7 | 0.64 | 6.58 | [45] |
| 5 | BDT-based low band gap polymer PBDTTT-CF | 0.76 | 15.2 | 0.66 | 7.73 | [46] |
| 6 | P3HT/PC60BM | 0.62 | 10.9 | 0.62 | 4.18 | [37] |
| 7 | D1:PCBM | 0.84 | 6.12 | 0.51 | 2.62 | [47] |
| 8 | PB:PCBM (annealed) | 0.80 | 7.9 | 0.56 | 3.54 | [7] |
| 9 | BDT-based low band gap polymer PBDTTT-S | 0.76 | 14.1 | 0.58 | 6.22 | [48] |
| 10 | MEH-PPV:PCBM:BCP | 0.75 | 2.95 | 0.44 | 0.98 | [49] |
| 11 | MEH-PPV:PCBM:Bphen | 0.74 | 3.98 | 0.44 | 1.30 | [49] |
| 12 | M2:PCBM | 0.68 | 3.94 | 0.46 | 1.23 | [50] |
| 13 | M2:F | 0.84 | 6.75 | 0.48 | 2.72 | [50] |
| 14 | PDTG-TPD polymer-based device | 0.86 | 14.0 | 0.67 | 8.1 | [51] |
| 15 | DCV5T-Bu4:PCBM [CB:CN (0.375%) as solvent] | 1.11 | 6.5 | 0.41 | 3.0 | [52] |
| 16 | DCV5T-Bu4:PCBM (ODCB as solvent) | 1.08 | 5.7 | 0.40 | 2.5 | [52] |
| 17 | BBTSBS/PCBM(annealed 120°C) | 0.62 | 0.56 | 0.29 | 0.10 | [53] |
| 18 | MEH-PPV:PCBM:GNP | 0.56 | 0.80 | 0.59 | 0.26 | [54] |
| 19 | P3HT:PCBM | 0.60 | 9.58 | 0.69 | 4.10 | [55] |
| 20 | P3HT/PC70BM with 2% n-dodecylthiol | 0.641 | 8.59 | 0.58 | 0.032 | [56] |
| 21 | Tempered P3HT:PCBM | 0.58 | -8.61 | 0.59 | 2.99 | [57] |
| 22 | PEDOT:PSS/PPABT:TiO2 nanoparticles | 0.26 | 1.29 | 0.37 | 0.125 | [58] |
| 23 | AnE-PVstat:PCBM | 0.825 | 5.13 | 0.58 | 2.46 | [59] |
| 24 | AnE-PVstat:PCBM with 0.01% of Ag NPs | 0.76 | 8.46 | 0.48 | 3.10 | [59] |
| 25 | PEDOT:PSS (P3HT/PCBM/PEDOT:PSS) | 0.60 | 11.92 | 0.62 | 4.43 | [60] |
| 26 | P3HT/PCBM/MoOx (annealed 250°C as a HEL) | 0.65 | 12.4 | 0.53 | 4.63 | [60] |
| 27 | AgInSe2.PCBM.P3HT | 0.50 | 3.71 | 0.40 | 0.75 | [61] |
| 28 | MEH-PPV:MAPbI3 | 0.81 | 9.11 | 0.36 | 3.0 | [43] |
In this paper, we have reported the photovoltaic response of the solution-processed bulk heterojunction (BHJ) solar cell based on the MEH-PPV:modified PCBM blend. The electrical and optical properties of the blend have been investigated. We have also observed the effect of thermal annealing on the photovoltaic performance of the MEH-PPV:modified PCBM or MEH-PPV:MPCBM-based devices.
2 Materials and methods
2.1 Materials and characterization methods
The polymer solar cells based on an interpenetrated network of conjugated polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and its modified form (MPCBM) were fabricated. MEH-PPV, PCBM, and PEDOT:PSS were purchased from Aldrich Chemicals and used as such. The modified PCBM (MPCBM) was supplied by Prof. Mikroyannidis, University of Patra, Greece and its synthesis was given elsewhere [41]. The chemical structure of the donor (MEH-PPV) and the acceptor (PCBM and Modified PCBM) is shown in Figure 1. All other materials and solvents were commercially purchased and were used as supplied. UV-vis spectra were recorded on a Hitachi-330 spectrometer with THF as solvent. The morphological images of the films were obtained from scanning electron microscope (Zeiss, 20 KV). The crystallinity of the blends was studied using the X-ray diffraction (XRD) technique (Panalytical make USA) having CuKα, as the radiation source of wavelength λ=1.5405 Å with the composite films coated on the quartz substrate. The current-voltage (J-V) measurement of the devices was carried out on a computer-controlled Keithley-238 source meter.
Chemical structures of (A) MEH-PPV, (B) PCBM, and (C) modified PCBM (MPCBM).
2.2 Device fabrication and characterization
The bulk heterojunction devices were fabricated according to the following procedure. First, the indium-doped tin oxide (ITO)-coated glass substrate was cleaned with detergent, then ultrasonicated in deionized water, acetone, and isopropyl alcohol and finally dried overnight in an oven at 80°C. To supplement this bottom electrode, a hole transport layer of PEDOT:PSS (BAYTRON, conductive grade) of thickness 80 nm was spin coated from aqueous solution on the ITO-coated glass substrate and was subsequently dried at 80°C for 20 min. However, Xu et al. has found efficiencies for the different ratios of MEH-PPV:PCBM blends (1:3, 1:4, and 1:5) and reported the highest efficiency for 1:4 ratio as 1.42% after annealing [62]. Thus, the blend solutions of MEH-PPV:PCBM (1:4) and MEH-PPV:MPCBM (1:4) were prepared using THF as a solvent in a concentration of 10 mg/ml and stirred for 2 h. The photoactive layer of the prepared blend solutions was deposited by spin coating on the top of the PEDOT:PSS layer. Finally, an aluminum (Al) electrode (thickness about 100 nm) was deposited by thermal evaporation under high vacuum (1×10-5 mbar). The effective area of the devices is 20 mm2. For thermal annealing, the blend films were placed on a hot plate and annealed at a temperature of 100°C for 10 min, before the deposition of Al electrode. The device structure is shown in Figure 2.
Schematic diagram of bulk heterojunction devices.
We have designated the devices based on different blends as follows:
ITO/PEDOT:PSS/MEH-PPV:PCBM/Al (Device D1).
ITO/PEDOT:PSS/MEH-PPV:MPCBM/Al (Device D2).
ITO/PEDOT:PSS/(MEH-PPV:MPCBM) thermally annealed/ Al (Device D3).
The current-voltage (J-V) measurement of these devices was carried out on a computer-controlled Keithley-238 source meter in the dark as well as under illumination. A halogen light source was used to give an irradiance of 100 mW/cm2 (equivalent of one sun at AM 1.5) at the surface of the device.
3 Results and discussion
3.1 Electrical properties of MEH-PPV and MPCBM
The energy level diagram of MEH-PPV, PCBM, and MPCBM are shown in Figure 3. The LUMO levels of PCBM and MPCBM are -3.95 eV and -3.80 eV, respectively. The LUMO level of MPCBM is raised by 0.15 eV in comparison with that of PCBM. The LUMO and HOMO levels of used materials were determined by using cyclic voltammetry (CV) measurements. To calculate the same, the following equations were used [63, 64]:
Energy level diagram of MEH-PPV, PCBM, and MPCBM.
where, Eredonset is the onset reduction potential measured in volts (V) versus Ag+/Ag.
Eoxonset is the onset oxidation potential measured in volts (V) versus Ag+/Ag.
This shift is attributed to the presence of the cyanovinylene 4-nitrophenyl segment in the molecule of MPCBM, which increase its electron affinity or acceptor strength. The higher LUMO energy level of MPCBM is desirable for its application as acceptor in polymer bulk heterojunction photovoltaic devices to get a higher Voc. As the LUMO (-3.80 eV) of MPCBM is very close to the work function of the Al (-4.1 eV) electrode, the interface between MPCBM and Al forms a nearly ohmic contact (barrier of about 0.30 eV) for electron injection from the LUMO level of MPCBM to Al. Similarly, the HOMO (-5.2 eV) of MEH-PPV is very close to the work function of PEDOT:PSS (-5.1 eV) electrode, the interface between MEH-PPV and ITO electrode form a nearly ohmic contact for hole injection from the HOMO level of MEH-PPV to ITO electrode. This indicates that MEH-PPV and MPCBM behave as p-type (electron donor) and n-type (electron acceptor) organic semiconductor, respectively.
It can be seen from the energy level diagram that the band gap of MEH-PPV is 2.20 eV, and the difference between the LUMO levels of MEH-PPV and MPCBM is about 0.80 eV. This difference is greater than the exciton binding energy, which is a prerequisite for efficient photoinduced charge separation in the BHJ active layer.
3.2 Optical properties of blends
The absorption spectra of MEH-PPV, PCBM, modified PCBM (MPCBM) and its blend are shown in Figure 4. It can be seen that the absorption spectra of the blend show the combination of the individual components. In particular, the absorption peak around 510 nm corresponds to MEH-PPV, which is associated with the interchain π-π* transition [65], whereas the peak around 630 nm corresponds mainly to MPCBM. The addition of PCBM to MEH-PPV shows an increment in the optical absorption which means that PCBM helps in light harvesting in the visible region. The absorption peaks of MPCBM appears in the UV region (<400 nm). Interestingly, MPCBM showed a much stronger absorption than PCBM for the region of 400–800 nm.
UV-vis absorption spectra of PCBM, MPCBM, MEH-PPV:PCBM, MEH-PPV:MPCBM and MEH-PPV:MPCBM thermally annealed.
The modified PCBM (MPCBM) showed a stronger absorption in the visible region of solar spectrum than PCBM due to the presence of the cyanovinylene 4-nitrophenyl segment [66, 67]. It has been well established that the incorporation of this segment to various polymers [3, 8] or small molecules [3, 4, 66, 67] broadened their absorption spectra and extended them into the near-infrared (NIR) region. The MEH-PPV:MPCBM blend also shows a broad absorption from 350 to 640 nm, which closely matches with the solar spectrum. Therefore, we expect more photons to be absorbed by the MEH-PPV:MPCBM blend compared to MEH-PPV:PCBM.
The blend with MPCBM shows not only a broader band absorption but also an enhanced intensity of the absorption, which is further increased when the blend is thermally annealed at 100°C for 10 min. This type of increase in the optical absorption after thermal annealing has been observed for conjugated polymers [68] and small molecules [69]. This feature is attributed to the aggregation/interchain interactions and the increase in the crystallinity of the material, which enhances the intensity of π-π* electronic transitions. Therefore, the carrier mobilities in the thermally annealed BHJ organic solar cells (OSCs) are more balanced and may be one of the factors increasing the PCE of the devices on the basis of the thermally annealed active layer. The thin film absorption of MEH-PPV:MPCBM blend also red shifts and displays more distinct vibronic structures, when blend is annealed at 100°C temperature for 10 min. The red shift in absorption of blend indicates an increased intermolecular ordering and planarity in the polymer backbone.
3.3 Photovoltaic properties of devices based on BHJ
The current-voltage (J-V) characteristics of the devices under illumination intensity of 100 mW/cm2 are shown in Figure 5. The photovoltaic parameters, i.e. short circuit current (Jsc), open circuit voltage (Voc), fill factor (FF), and PCE of the devices are listed in Table 2. It can be seen from this table that the Voc is increased from 0.75 V for PCBM-based device to 0.89 V for the MPCBM-based device. The higher value of Voc for the PSC device based on MEH-PPV:MPCBM is attributed to the higher LUMO energy level of MPCBM because it is well known that the Voc of PSCs is proportional to the difference between the HOMO of the donor and the LUMO of the acceptor [70]. The increase in the Jsc for the device based on the MEH-PPV:MPCBM in comparison to MEH-PPV:PCBM is attributed to the broader absorption of the MEH-PPV:MPCBM blend, which causes an enhancement in the photogenerated excitons in the blend, resulting in a slightly higher photocurrent.
J-V characteristics curve of different designated devices.
Photovoltaic parameters of devices D1, D2, and D3.
| Devices | Short circuit current (Jsc) (mA/cm2) | Open circuit voltage (Voc) (V) | Fill factor (FF) | Power conversion efficiency (η%) |
|---|---|---|---|---|
| (D1) | 5.60 | 0.75 | 0.31 | 1.30 |
| (D2) | 5.90 | 0.89 | 0.34 | 1.78 |
| (D3) | 6.20 | 0.90 | 0.35 | 1.95 |
3.4 X-ray diffraction
Thin film XRD was used to determine the differences in crystallinity of the blended films before and after thermal annealing. Figure 6 gives the diffraction patterns of the as-cast and annealed blends. The as-cast blend film exhibits a peak centered at 2θ=5.0° as shown in Figure 6. The diffraction intensity of the thermally annealed blend increases, which indicates a higher degree of crystallinity. These changes in the film crystallinity after thermal annealing agree with what is observed in the absorption spectra. Because most of the fullerene acceptors, such as PCBM, do not show any diffraction patterns in the range of 2θ values used [71], the changes in crystallinity of the blended film after thermal annealing are mainly attributed to an increase in crystallite size of the donor material (MEH-PPV). The increase in the crystallinity of MEH-PPV upon thermal annealing leads to an improvement in the hole mobility that increases the overall PCE.
XRD patterns of MEH-PPV:MPCBM blend and thermally annealed blend.
3.5 Surface morphology
The morphology of the spin-coated polymer thin films is an important factor to fabricate polymer solar cells [72, 73]. The surface morphological changes of MEH-PPV:modified fullerene (1:4) films and its thermally annealed films were monitored using SEM as shown in Figure 7A and B, respectively. It can be clearly seen from the SEM images that surface morphology of the thermally annealed MEH-PPV:MPCBM layers shows higher surface peaks and an obvious increase in surface roughness as shown in Figure 7B. This can be the result of an increased nanoscaled phase separation between the crystalline MEH-PPV and the modified PCBM (MPCBM) acceptor. Increase in surface roughness allows more space for MEH-PPV crystallites to form, thus, increases crystallinity (as per proved by XRD pattern) as well as interfacial contact area between the PEDOT:PSS and MEH-PPV:MPCBM layer. This allows more efficient hole collection at the anode, which improves Jsc and FF and also increases absorption of the active layer.
SEM images of (A) MEH-PPV:MPCBM film and (B) MEH-PPV:MPCBM thermally annealed blend films.
4 Conclusions
We have fabricated polymer solar cells with the MEH-PPV:MPCBM blend, sandwiched between ITO/PEDOT:PSS and Al electrodes. The Voc and Jsc values of the BHJ device based on MEH-PPV:MPCBM blend cast from THF solvent reached 0.90 V and 5.90 mA/cm2, respectively, leading to an overall PCE of ~1.78%, which is significantly improved compared to a BHJ device based on MEH-PPV:PCBM (1.30%). The increase in Jsc has been attributed to the stronger absorption of MPCBM in the visible region, which is missing for PCBM. However, the increase in the Voc has been ascribed to the higher LUMO. Moreover, this has been further increased to 1.95%, when the MEH-PPV:MPCBM blend was thermally annealed before the deposition of the Al electrode. We have observed that the improvement in the PCE has been mainly attributed to the increase in the Jsc.
About the authors
Shyam S. Sharma is an Assistant Professor at the Government Women Engineering College in Ajmer, India. He qualified in the CSIR-NET, SLET, and GATE. He has more than 13 years’ experience teaching physics. He received his PhD degree from the University of Rajasthan, Jaipur, in the field of Organic Electronics. He has more than 40 research publications in international journals and proceedings of international and national conferences, and has published a book on Synthesis and characterization of organic photovoltaic cells. His research interest is in the area of organic semiconductor materials and devices for electronic and optoelectronic technology. He has been honored for his research work with an Innovative Engineer Award from United Engineers Council. He is a life member of the Indian Physics Association (IPA), Indian Association of Physics Teacher (IAPT), and Material Research Society of India (MRSI).
Khushboo Sharma is a Research Scholar at Bhagwant University in Ajmer, India. She did her Master’s degree in Physics. Currently, she is a project fellow under the Department of Science and Technology, SERB Division, New Delhi project, entitled Development of New Materials for Dye-Sensitized Solar Cells at Government Women Engineering College, Ajmer, India.
G.D. Sharma is a Director of Research & Development Centre, JEC group of Colleges, Jaipur Engineering College Campus, Jaipur, India. He completed his MSc in Physics. He received his PhD degree from IIT Delhi in the field of Organic Electronics and Optoelectronics Devices. He has overseen 16 PhDs. More than 40 students have completed their MSc project and about 100 students have completed their BSc (Electronics) project under his supervision. He has collaborated with the International Society of Optical Engineering (USA); DRDO, Jodhpur; University of Patras, Greece; IISc, Bangalore; National University of Singapore; Behna University, Egypt; IIT, Roorkee; MANIT, Bhopal; University of Bath, UK and IICT, Hyderabad. He has published more than 170 research papers. His research interest is in the areas of purification of materials, fabrication of devices and their characterization, fabrication and characterization P-N junction devices, materials science, organic semiconductors for photovoltaic devices and light emitting devices, nano-materials and technology, piezoelectric and pyro-electric properties of organic polymer.
Acknowledgments:
The authors are thankful to Prof. John A. Mikroyanndis, Chemical Technology Laboratory, University of Patra, Greece for providing MPCBM. We are also grateful to Centre for Development of Physics Education and USIC, University of Rajasthan, Jaipur, India for providing experimental and measurement facilities.
References
[1] Nalwa HS, Eds., Handbook of Organic Conductive Molecules and Polymers, vols. 1–4, Wiley: New York, 1997.Search in Google Scholar
[2] Peumans P, Yakimov A, Forrest SR. Small molecular weight organic thin-film photodetectors and solar cells. J. Appl. Phys. 2003, 93, 3693.Search in Google Scholar
[3] Mikroyannidis JA, Sharma SS, Vijay YK, Sharma GD. Novel low band gap small molecule and phenylenevinylene copolymer with cyanovinylene 4-nitrophenyl segments: synthesis and application for efficient bulk heterojunction solar cells. ACS Appl. Mater. Interfaces 2009, 2, 270–278.10.1021/am9006897Search in Google Scholar
[4] Mikroyannidis JA, Kabanakis AN, Kumar A, Sharma SS, Vijay YK, Sharma GD. Synthesis of a low-band-gap small molecule based on acenaphthoquinoxaline for efficient bulk heterojunction solar cells. Langmuir 2010, 26, 12909–12916.10.1021/la1016966Search in Google Scholar PubMed
[5] Bettignies Rde, Nicolas Y, Blanchard P, Levillain E, Nunzi JM, Roncali J. Planarized star-shaped oligothiophenes as a new class of organic semiconductors for heterojunction solar cells. Adv. Mater. 2003, 15, 1939–1943.Search in Google Scholar
[6] Cremer J, Bauerle P. Star-shaped perylene-oligothiophene-triphenylamine hybrid systems for photovoltaic applications. J. Mater. Chem. 2006, 16, 874–884.Search in Google Scholar
[7] Mikroyannidis JA, Sharma GD, Sharma SS, Vijay YK. Novel low band gap phenylenevinylene copolymer with BF2-Azzopyrole complex units: synthesis and use of efficient bulk heterojunction solar cells. J. Phys. Chem. C 2010, 114, 1520–1527.10.1021/jp910467cSearch in Google Scholar
[8] Mikroyannidis JA, Kabanakis AN, Balraju P, Sharma GD. Enhanced performance of bulk heterojunction solar cells using novel alternating phenylenevinylene copolymers of low band gap with cyanovinylene 4-nitrophenyls. Macromolecules 2010, 43, 5544–5553.10.1021/ma100943tSearch in Google Scholar
[9] Yu G, Heeger AJ. Charge separation and photovoltaic conversion in polymer composites with internal donor acceptor heterojunctions. J. Appl. Phys. 1995, 78, 4510–4515.Search in Google Scholar
[10] Padinger F, Rittberger RS, Sariciftic NS. Effects of postproduction treatment on plastic solar cells. Adv. Funct. Mater. 2003, 13, 85–88.Search in Google Scholar
[11] Hayashi Y, Yamada I, Takagi S, Takasu A, Soga T, Jimbo T. Influence of structure and C60 composition on properties of blends and bilayers of organic donor-acceptor polymer/C60 photovoltaic devices. Jpn. J. Appl. Phys. 2005, 44, 1296–1300.Search in Google Scholar
[12] Vijay YK, Sharma SS. Synthesis and Characterization of Organic Photovoltaic Cells, VDM: Germany, 2010.Search in Google Scholar
[13] Mikroyannidis JA, Kabanakis AN, Sharma SS, Sharma GD. A simple and effective modification of PCBM for use as an electron acceptor in efficient bulk heterojunction solar cells. Adv. Funct. Mater. 2011, 21, 746.Search in Google Scholar
[14] Coakley KM, McGehee MD. Conjugated polymer photovoltaic cells. Chem. Mater. 2004, 16, 4533.Search in Google Scholar
[15] Naarmann H. Structure and conductivity of organic polymers. Angew. Chem. Int. Ed. 1969, 8, 915–916.Search in Google Scholar
[16] Feist FA, Basché T. Fluorescence excitation and emission spectroscopy on single MEH-PPV chains at low temperature. J. Phys. Chem. B 2008, 112, 9700–9708.10.1021/jp802585mSearch in Google Scholar PubMed
[17] Wang PS, Lu HH, Liu CY, Chen SA. Gel formation via physical cross-linking in the soluble conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4- phenylenevinylene], in solution by addition of alkanes. Macromolecules 2008, 41, 6500–6504.10.1021/ma800076gSearch in Google Scholar
[18] Yu HZ, Peng JB. Performance and lifetime improvement of polymer/fullerene blend photovoltaic cells with a C60 interlayer. Org. Electron 2008, 9, 1022–1025.10.1016/j.orgel.2008.07.010Search in Google Scholar
[19] Yakuphanoglu F. Photovoltaic properties of the organic-inorganic photodiode based on polymer and fullerene blend for optical sensors. Sens. Actuat. A 2008, 141, 383–389.10.1016/j.sna.2007.10.023Search in Google Scholar
[20] Nayak RR, Nag OK, Woo HY, Hwang S, Vak D, Korystov D, Jin Y, Suh H. Synthesis and fluorescence study of water-soluble conjugated polymers for efficient FRET-based DNA detection. Curr. Appl. Phys. 2009, 9, 636–642.Search in Google Scholar
[21] Sohn S, Park K, Lee D, Jung D, Kim HM, Manna U, Yi J, Boo J, Chae H, Kim K. Characteristics of polymer light emitting diodes with the LiF anode interfacial layer. Jpn. J. Appl. Phys. 2006, 45, 3733.Search in Google Scholar
[22] Sariciftic NS, Polymeric photovoltaic materials, Curr. Opin. Solid State Mater. Sci. 1999, 4, 373.Search in Google Scholar
[23] Kong F, Huang GS, Yang YM, Yang CZ, Bao XM, Yuan RK. Conformation and luminescence characteristics of nano poly[2-metoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] in two-dimensional arrays. J. Polym. Sci. B Polym. Phys. 2006, 44, 3037–3041.Search in Google Scholar
[24] Alem S, Bettignies Rde, Nunzi JM. Efficient polymer-based interpenetrated network photovoltaic cells. Appl. Phys. Lett. 2004, 84, 2178–2180.Search in Google Scholar
[25] Zhang F, Johansson M, Andersson MR, Hummenlen JC, Inganas O. Polymer photovoltaic cells with conducting polymer anodes. Adv. Mater. 2002, 14, 662–665.Search in Google Scholar
[26] Kim H, Kim JY, Lee K, Park Y, Jin Y, Suh H. Organic photovoltaic cells based on conjugated polymer/fullerene composites. Curr. Appl. Phys. 2001, 1, 139–143.Search in Google Scholar
[27] Zhang FL, Johansson M, Andersson MR, Hummelen JC, Inganas O. Polymer solar cells based on MEH-PPV and PCBM. Synth. Met. 2003, 137, 1401–1402.Search in Google Scholar
[28] Li YF, Yang LY, Qin WJ, Yin SG, Zhang FL. Efficiency enhancement of MEH-PPV:PCBM solar cells by addition of ditertbutyl peroxide as an additive. Chin. Phys. Lett. 2013, 30, 017202.Search in Google Scholar
[29] Truong NTN, Park C, Jung JH. Investigation of morphology of an MEH-PPV: PCBM active layer and its application to bulk hetero-junction solar cell performance. J. Korean Phys. Soc. 2012, 60, 2029–2033.Search in Google Scholar
[30] Matsuo Y. Design concept for high-LUMO-level fullerene electron-acceptors for organic solar cells. Chem. Lett. 2012, 41, 754–759.10.1246/cl.2012.754Search in Google Scholar
[31] Sanchez-Diaz A, Izquierdo M, Filippone S, Martin N, Palomares E. The origin of the high voltage in DPM12/P3HT organic solar cells. Adv. Funct. Mater. 2010, 20, 2695–2700.Search in Google Scholar
[32] Yoo SH, Kum JM, Cho SO. Tuning the electronic band structure of PCBM by electron irradiation. Nanoscale Res. Lett. 2011, 6, 545.Search in Google Scholar
[33] Yang C, Li H, Sun Q, Qiao J, Li Y, Li Y, Zhu D. Photovoltaic cells based on the blend of MEH-PPV and polymers with substituents containing C60 moieties. Sol. Energy Mater. Sol. Cells 2005, 85, 241–249.10.1016/j.solmat.2004.03.007Search in Google Scholar
[34] Xu Z, Chen LM, Yang GW, Huang CH, Hou JH, Wu Y, Li G, Hsu CS, Yang Y. Vertical phase separation in poly(3-hexylthiophene):fullerene derivative blends and its advantage for inverted structure solar cells. Adv. Funct. Mater. 2009, 19, 1227–1234.Search in Google Scholar
[35] Yang CD, Kim JY, Cho S, Lee JK, Heeger AJ, Wudl F. Functionalized methanofullerenes used as n-type materials in bulk-heterojunction polymer solar cells and in field-effect transistors. J.Am. Chem. Soc. 2008, 130, 6444–6450.Search in Google Scholar
[36] Zhang Y, Yip HL, Acton O, Hau SK, Huang F, Jen AKY. A simple and effective way of achieving highly efficient and thermally stable bulk-heterojunction polymer solar cells using amorphous fullerene derivatives as electron acceptor. Chem. Lett. 2009, 21, 2598–2600.Search in Google Scholar
[37] Choi JH, Son KI, Kim T, Kim K, Ohkubo K, Fukuzumi S. Thienyl-substituted methanofullerene derivatives for organic photovoltaic cells. J. Mater. Chem. 2010, 20, 475–482.Search in Google Scholar
[38] Lenes M, Wetzelaer GJAH, Kooistra FB, Veenstra SC, Hummelen JC, Blom PWM. Fullerene bisadducts for enhanced open-circuit voltages and efficiencies in polymer solar cells. Adv. Mater. 2008, 20, 2116–2119.Search in Google Scholar
[39] Lenes M, Shelton SW, Sieval AB, Kronholm DF, Hummelen JC, Blom PWM. Electron trapping in higher adduct fullerene-based solar cells. Adv. Funct. Mater. 2009, 19, 3002–3007.Search in Google Scholar
[40] Ross RB, Cardona CM, Guldi DM, Sankkaranarayanan SG, Reese MO, Kopidakis N, Peet J, Walker B, Bazan G, Keuren EV, Holloway BC, Drees M. Endohedral fullerenes for organic photovoltaic devices. Nat. Mater. 2009, 8, 208–212.Search in Google Scholar
[41] Mikroyannidis JA, Tsagkournos DV, Sharma SS, Sharma GD. Synthesis of a broadly absorbing Modified PCBM and application as electron acceptor with poly (3-hexylthiophene) as electron donor in efficient bulk heterojunction solar cells. J. Phys. Chem. C 2011, 115, 7806–7816.10.1021/jp201337uSearch in Google Scholar
[42] Matsuo Y, Kawai J, Inada H, Nakagawa T, Ota H, Otsubo S, Nakamura E. Addition of dihydromethano group to fullerenes to improve the performance of bulk heterojunction organic solar cells. Adv. Mater. 2013, 25, 6266–6269.Search in Google Scholar
[43] Masi S, Colella S, Listorti A, Roiati V, Liscio A, Palermo V, Rizzo A, Gigli G. Growing perovskite into polymers for easy-processable optoelectronic devices. Sci. Rep. 2015, 5, 7725.Search in Google Scholar
[44] Liang Y, Feng DQ, Wu Y, Tsai ST, Li G, Ray C, Yu LP. Highly efficient solar cell polymers developed via fine-tuning of structural and electronic properties. J. Am. Chem. Soc. 2009, 131, 7792–7799.Search in Google Scholar
[45] Hou JH, Chen HY, Zhang SQ, Chen RI, Yang Y, Wu Y, Li G. Synthesis of a low band gap polymer and its application in highly efficient polymer solar cells. J. Am. Chem. Soc. 2009, 131, 15586–15587.Search in Google Scholar
[46] Chen HY, Hou JH, Zhang SQ, Liang YY, Yang GW, Yang Y, Yu LP, Wu Y, Li G. Polymer solar cells with enhanced open-circuit voltage and efficiency. Nat. Photon. 2009, 3, 649–653.Search in Google Scholar
[47] Mikroyannidis JA, Tsagkournos DV, Sharma SS, Kumar A, Vijay YK, Sharma GD. Efficient bulk heterojuntion solar cells based on low band gap bisazo dyes containing anthracene and/or pyrrole units. Sol. Energy Mat. Sol. C 2010, 94, 2318–2327.10.1016/j.solmat.2010.08.001Search in Google Scholar
[48] Huang Y, Huo LJ, Zhang SQ, Guo X, Han C, Li YF, Hou JH. Sulfonyl: a new application of electron-withdrawing substituent in highly efficient photovoltaic polymer. Chem. Commun. 2011, 47, 8904–8906.Search in Google Scholar
[49] Liu XD, Zhao SL, Xu S, Zhang FJ, Zhang TH, Gorg W, Yan G, Kong C, Wang YS, Xu XR. Performance improvement of MEH-PPV: PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers. Chin. Phys. B 2011, 20, 068801.10.1088/1674-1056/20/6/068801Search in Google Scholar
[50] Mikroyannidis JA, Tsagkournos DV, Sharma SS, Vijay YK, Sharma GD. Low band gap conjugated small molecules containing benzobisthiadiazole and thiionthiadiazole central units: synthesis and application for bulk heterojunction solar cells. J. Mater. Chem. 2011, 21, 4679.Search in Google Scholar
[51] Small CE, Chen S, Subbiah J, Amb CM, Tsang SW, Lai TH, Reynolds JR, So F. High-efficiency inverted dithienogermole–thienopyrrolodione-based polymer solar cells. Nat. Photon. 2012, 6, 115–120.Search in Google Scholar
[52] Schulz GL, Urdanpilleta M, Fitzner R, Brier E, Osteritz EM, Reinold E, Bauerle P. Optimization of solution processed oligothiophene:fullerene based organic solar cells by using solvent additives. Beilstein J. Nanotechnol. 2013, 4, 680–689.Search in Google Scholar
[53] Amro K, Thakur AK, Berthelot JR, Poriel C, Hirsch L, Douglas WE, Clément S, Gerbier P. 2,5-Thiophene substituted spirobisiloles – synthesis, characterization, electrochemical properties and performance in bulk heterojunction solar cells. New J. Chem. 2013, 37, 464–473.Search in Google Scholar
[54] Sharma SS, Sharma V, Singh R, Srivastava S, Sharma P, Vijay YK. Bulk heterojunction solar cells based on graphene nanoplatelets. Adv. Electrochem. 2013, 1, 128–132.Search in Google Scholar
[55] Huang JH, Hsiao YS, Richard E, Chen CC, Chen P, Li G, Chu CW, Yang Y. The investigation of donor-acceptor compatibility in bulk-heterojunction polymer systems. Appl. Phys. Lett. 2013, 103, 043304.Search in Google Scholar
[56] Algazzar MI. Enhancing the structure and performance of P3HT/PC70BM polymer solar cells with N-dodecylthiol. Theses and Dissertations 2014. Paper 487. University of Wisconsin Milwaukee, UWM Digital Commons.Search in Google Scholar
[57] Maibach J, Adermann T, Glaser T, Eckstein R, Mankel E, Pucci A, Müllen K, Lemmer U, Hamburger M, Mayer T, Jaegermann W. Impact of processing on the chemical and electronic properties of phenyl-C61-butyric acid methyl ester. J. Mater. Chem. C 2014, 2, 7934–7942.10.1039/C4TC00769GSearch in Google Scholar
[58] Pokhrel B, Dolui SK. Synthesis, characterization and photovoltaic property evaluation of poly (3-phenyl azomethine alkyl thiophene)s. National Conference on Recent Advances in Civil Engineering (NCRACE-2013, 15–16 November). Int. J. Innovative Res. Sci. Eng. Technol. 2014, 3, 184–189.Search in Google Scholar
[59] Tore N, Parlak EA, Tumay TA, Kavak P, Sarıoğlan S, Bozar S, Günes S, Ulbricht C, DAM Egbe. Improvement in photovoltaic performance of anthracene-containing PPE–PPV polymer-based bulk heterojunction solar cells with silver nanoparticles. J. Nanopart. Res. 2014, 16, 2298.Search in Google Scholar
[60] Li B, Ren H, Yuan H, Karim A, Gong X. Room-temperature, solution-processed MoOx thin film as a hole extraction layer to substitute PEDOT/PSS in polymer solar cells. ACS Photonics2014, 1, 87–90.10.1021/ph4000168Search in Google Scholar
[61] Pathak D, Wagner T, Adhikari T, Nunzi JM. AgInSe2.PCBM.P3HT inorganic organic blends for hybrid bulk hetero junction photovoltaics. Synth. Met. 2015, 200, 102–108.Search in Google Scholar
[62] Song JL, Xu Z, Zhang FJ, Zhao SL, Hu T, Li JM, Liu XD, Yue X, Wang YS. The effect of annealing treatment on the performance of bulk heterojuntion solar cells with donor and acceptor different weight ratios. Sci. China. Ser. G 2009, 52, 1606–1610.10.1007/s11433-009-0220-0Search in Google Scholar
[63] Sun QJ, Wang HQ, Yang CH, Li YF. Synthesis and electroluminescence of novel containing crown ether spacers. J. Mater. Chem. 2003, 13, 800–806.Search in Google Scholar
[64] Hou JH, Tan ZA, Yan Y, He YJ, Yang CH, Li YF. Synthesis and optical properties of two-dimensional conjugated polythiophenes with bi(thienylenevinylene) side cahins. J. Am. Chem. Soc. 2006, 128, 4911–4916.Search in Google Scholar
[65] Kim SS, Jo J, Chun C, Hong JC, Kim DY. Hybrid solar cells with ordered TiO2 nanostructures and MEH-PPV. J. Photochem. Photobiol. A: Chem. 2007, 188, 364–370.Search in Google Scholar
[66] Mikroyannidis JA, Stylianakis MM, Balraju P, Suresh P, Sharma GD. Novel p-phenylenevinylene compounds containing thiophene or anthracene moieties and cyano-vinylene bonds for photovoltaic applications. ACS Appl. Mater. Interfaces 2009, 1, 1711–1718.10.1021/am900270sSearch in Google Scholar PubMed
[67] Mikroyannidis JA, Suresh P, Sharma GD. Synthesis of benzoselenadiazole-based small molecule and phenylenevinylene copolymer and their application for efficient bulk heterojunction solar cells. Org. Electron. 2010, 11, 311.Search in Google Scholar
[68] Brabec CJ, Cravino A, Meissner D, Sariciftci NS, Fromherz T, Rispens MT, Sanchez L, Hummelen JC. Origin of the open circuit voltage of plastic solar cells. Adv. Funct. Mater. 2001, 11, 374–380.Search in Google Scholar
[69] Erb T, Zhokhavets U, Gobsch G, Raleva S, Stuhn B, Schilinsky P, Waldauf C, Brabec CJ. Correlation between structural and optical properties of composite polymer/fullerene films for organic solar cells. Adv. Funct. Mater. 2005, 15, 1193–1196.Search in Google Scholar
[70] Walker B, Tamayo AB, Dang XD, Zalar P, Seo JH, Garcia A, Tantiwiwat M, Nguyen TQ. Nanoscale phase separation and high photovoltaic efficiency in solution-processed, small-molecule bulk heterojunction solar cells. Adv. Funct. Mater. 2009, 19, 3063–3069.Search in Google Scholar
[71] Chikamatsu M, Nagamatsu S, Yoshida Y, Saito K, Yase K. Solution-processed n-type organic thin-films transistors with high field-effect mobility. Appl. Phys. Lett. 2005, 87, 203504.Search in Google Scholar
[72] Ma WL, Yang CY, Gong X, Lee K, Heeger AJ. Thermally stable, efficient polymer solar cells with nanoscale control of the interpenetrating network morphology. Adv. Funct. Mater. 2005, 15, 1617–1622.Search in Google Scholar
[73] Li G, Shrotriya V, Huang J, Yao Y, Moriarty T, Emery K, Yang Y. High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nat. Mater. 2005, 4, 864–868.Search in Google Scholar
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