The blend ratio effect on the photovoltaic performance and stability of poly (3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and poly(3-octylthiophene):PCBM solar cells
Highlights
► On Decreasing PCBM content, needle like structures declined for P3OT blends. ► The shunt resistances of solar cells increased with decreasing PCBM content. ► The blend ratios affect leakage current and morphology of the devices. ► ISOS-L-1 testing indicated that all devices are very durable for 300 min.
Introduction
Bulk heterojunction solar cells made from conjugated polymers and fullerenes have gained popularity and seen a rapid progression of improvements in the techniques as detailed in a series of reviews [1], [2], [3], [4], [5], [6] and special issues [7], [8], [9], [10]. Significant progress in BHJ solar cells has been made by the synthesis of low band gap conjugated polymers and optimization of the device preparation conditions, including the application of adjusting the volume fractions of the components [11], [12], [13], thermal annealing treatments [14], [15]and solvent annealing [16], [17]. During the last two years, progress in polymer/fullerene based solar cells was so rapid that new efficiency records were published frequently via news articles or web pages before full publications could follow, as seen with the recent 7.6% efficiency world record announced by Solarmer [18]. It has been shown that both the conditions for processing of these mixtures from solution and post production treatment can have a large influence on the performance of these devices, because they affect the morphology and phase separation of the active layer [19], [20].
Materials with high absorption coefficients are necessary for applications in polymer solar cells. This is due to the requirement that the film thickness of photoactive layer should normally not exceed some hundreds of nanometers (100–300 nm). The absorption maximum (λmax) of P3HT and P3OT can be observed at 500 nm (2.48 nm) and 512 nm (2.42 eV), respectively. These λmax values when correlated with the energy of π→π⁎ band transition indicate more pronounced planarity of the backbone chains for P3OT than for P3HT. This is due to the fact that longer side groups restrict the number of possible conformations. P3OT chains can be well-planarized, giving more extended π conjugation than P3HT, which may increase the device performance. In addition, polymers with longer side-chains can be better dissolved by solvent molecules. Consequently P3OT chains with longer side-chains have more expanded structures in solutions. So fullerene can move freely during the film formation that can lead to better charge transport properties.
In this study, we investigate the blend ratio effect on photovoltaic performance of P3HT:PCBM and P3OT:PCBM solar cells and also morphology of blends was studied. The photovoltaic parameters and morphology of P3HT:PCBM and P3OT:PCBM blends are also compared.
Section snippets
Materials and solutions
Regioregular poly(3-hexylthiophene), poly(3-octylthiophene) as a donor and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), as an electron acceptor, were purchased from Sigma-Aldrich. PEDOT–PSS (500 P) were purchased from Clevios. The chemical structures of P3HT, P3OT and PCBM are shown in Fig. 1. Concentrations of P3HT and P3OT were 20 mg/mL; the solvent was 1,2 dichlorobenzene from Sigma-Aldrich.
Film and device fabrication
All cells were fabricated on indium tin oxide (ITO) coated glass substrates with a sheet
Device performance under illumination
Table 1 depicts the effect of blend ratio on PV parameters of P3HT:PCBM and P3OT:PCBM solar cells (Fig. 2). It indicates that power conversion efficiency (PCE) of both solar cells increased with decreasing PCBM content. The Voc of the polymer solar cells slightly increases with decreasing PCBM ratio (from 1 to 0.8). The changes in the performance parameters, such as Voc and Jsc, cannot be explained only by the changes in the overall polymer crystallinity for bulk heterojunction systems. It has
Conclusion
In this study we reported the blend ratio effect on photovoltaic performance of P3HT:PCBM and P3OT:PCBM solar cells and also morphology of blends. The results showed that power conversion efficiencies of P3HT:PCBM and P3OT:PCBM solar cells increased with decreasing PCBM content. The blend ratios of P3HT:PCBM and P3OT:PCBM solar cells affect carrier concentration, leakage current and series of resistance and morphology of the devices. The shunt resistances of P3HT:PCBM and P3OT:PCBM solar cells
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2017, Organic ElectronicsCitation Excerpt :For P3OT-, P3HT-, and P3BT based OPV devices with MDBS, the highest PCEs are similar to the higher values reported in the literature. In particular, for P3OT, to the best of our knowledge, most of the reported PCEs of P3OT/PCBM BHJ OPV devices with or without post-treatment are below 1.0% [33–36]. The highest PCE of P3OT/PCBM BHJ OPV without post-treatment, reported by He's group, is 1.53% with the addition of 8 wt% solution-processable functionalized graphene (SPFGraphene) [37].
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Improved photovoltaic performance of silicon nanowires/conjugated polymer hybrid solar cells
2014, Synthetic MetalsCitation Excerpt :The bulk heterojunction structure composed of interpenetrating network of polymer donor and electron acceptor has deeply promoted the development of polymer solar cells [4,5]. Both inorganic and organic electron acceptors are investigated; the latter are mainly fullerene derivatives [6–8]. Although power conversion efficiency (PCE) of polymer solar cells with these fullerene derivatives electron acceptors reached up to 9%, the complicated synthesis process and easy oxidation of fullerene in ambient still hinder their practical investigation [9,10].