Efficient and hysteresis-less pseudo-planar heterojunction perovskite solar cells fabricated by a facile and solution-saving one-step dip-coating method

doi:10.1016/j.orgel.2016.10.035

Organic Electronics

Volume 40, January 2017, Pages 13-23

https://doi.org/10.1016/j.orgel.2016.10.035 Get rights and content

Highlights

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Pseudo-planar heterojunction perovskite solar cell was reported for the first time.
•
The device was fabricated by a solution-saving one-step dip-coating method.
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The device shows PCE close to that of a conventional spin-coated one.
•
Models of the abnormal hysteresis, roll-over and current peak were proposed.

Abstract

Rough dense sol-gel-derived titanium dioxide (TiO₂) electron-transport layers (ETLs) and smooth organolead halide perovskite (PVK) films for pseudo-planar heterojunction perovskite solar cells (P-PH PVKSCs) were fabricated by a facile one-step dip-coating method. The highly compact TiO₂ ETLs and uniform PVK films endow the device a high power conversion efficiency (PCE) of over 11%, which was nearly identical to that of a reference device (12%) fabricated by conventional spin-coating. Furthermore, the device showed no pronounced hysteresis when tested by scanning the voltage in a forward and backward direction, showing the potential of facile and waste-free dip-coating in replacing of spin-coating for large area perovskite solar cells preparation. Lastly, the hysteresis was compared and discussed and models regarding the abnormal hysteresis, roll-over and current peak phenomena were proposed as well.

Graphical abstract

Efficient and hysteresis-less pseudo-planar heterojunction perovskite solar cell fabricated by a facile and solution-saving one-step dip-coating method was proposed for the first time. The device shows a high power conversion efficiency of over 11%, closing to that of a reference device (12%) fabricated by conventional spin-coating. Models regarding the abnormal hysteresis, roll-over and current peak phenomenons were proposed as well.

Introduction

Organic-inorganic hybrid halide perovskite (e.g., CH₃NH₃PbX₃; X = Cl, Br, I) based solar cells have recently become the focal point of the photovoltaic (PV) community as a promising next-generation PV technology. The certified efficiency of a single-junction perovskite solar cell (PVKSC) has reached 20.1% after only 5 years of active research [1], [2], [3], [4]. The superior photoelectric properties of PVK material are mainly attributed to the combination of direct-band-gap p-p transitions, ability to absorb light over the entire visible spectrum, larger carrier lifetime and diffusion length [5], [6], [7]. In addition, such a device with high crystallinity perovskite layers can be formed by a simple spin-coating method. Actually, at present, for most of the devices, including those certified efficiency breakthrough device, their perovskite layers were deposited on planar or mesoscopic metal oxide substrates by the spin-coating technique with a one-step or two-step approach [4]. For PVKSCs, it is widely accepted that the photovoltaic performance is greatly dependent on the perovskite film morphology, which relies on the deposition method, annealing process and solvents employed [8], [9]. Despite of rapid progress in the making of high-quality perovskite films and the achieving of high device performance, exploring a suitable printing technique for the controllable and scalable production of the perovskite layers is highly expected when considering their practical applications [10]. Especially, spin coating is only suitable for the preparation of a small area film in the laboratory level for research use only. Film of a larger area prepared by spin-coating will appear uneven thickness distribution along the radial direction (Fig. S1), which will lead to uneven distribution of device efficiency on a substrate (Fig. S7), limiting the large-scale practical application of spin-coating [11]. Furthermore, the spin-coating is a very solution-wasting method for preparing film (Fig. S2). In our experiments, by deciding the weight change of substrate before and after the deposition of perovskite film (Fig. S3 and Table S1), we found that the effective utilization of the precursor solution is less than 4%. Taking into account these problems, we need to explore a simple and fast solution-based technique instead of spin-coating for the preparation of large-area PVKSCs, especially for the current situation that the efficiency (20.1%) has exceeded the lowest efficiency (15%) needed for commercialization [12]. Recently, there have been works reported on some other wet methods for the preparation of perovskite film, including inkjet printing, doctor-blading, electro-spray deposition, compressed air blow-drying, delivering various efficiencies with potential for large-area device fabrication [12], [13], [14], [15]. Dip-coating is an ideal method to prepare thin films from chemical solutions since it is a low-cost and waste-free process that is easy to scale up and offers a good control on thickness. Dip-coated films are free of pits and pinholes [16], [17]. For such reasons, it has been a popular choice in the fabrication of various optoelectronic devices including light-emitting devices, solar cells and field-effect transistors [18], [19], [20]. In our previous work, polymer: fluorine bulk heterojunction organic photovoltaic devices were fabricated by the technique to achieve high-quality dip-coated photoactive layers [21].

In this work, we report a facile dip-coating route to sequentially prepare a dense sol-gel-derived titanium dioxide (TiO₂) electron-transport layer (ETL) and a smooth organolead halide perovskite film for PH PVKSC. This method does not require any complicated equipment and does not rely on the non-scalable spin-coating therefore has great potential in large-scale roll-to-roll fabrication of perovskite light absorbing film. A power conversion efficiency (PCE) of over 11% was demonstrated by simply using spiro-MeOTAD as the hole transporter and Ag as anode.

Section snippets

Materials

Lead chloride (PbCl₂, 99.999%), Diethanolamine (98%), 4-tert-Butylpyridine (4-tBP) and TiCl₄ were purchased from Sigma-Aldrich CH₃NH₃I from Shanghai Materwin New Materials Co. Ltd., Titanium (IV) isopropoxide (98+%) and Li-bis (trifluoromethanesulfonyl) imide (Li-TFSI) from Acros, spiro-OMeTAD (99.0%) from Shenzhen Feiming Science and Technology Co. Ltd, dimethylformamide (DMF, J&K reagent, 99.99%), acetonitrile, isopropanol, ethanol and chlorobenzene (CB) from Shanghai Chemical Agent Ltd.,

Results and discussion

Scheme 1 shows the scheme of perovskite solar cell device fabrication process. The complete device fabrication involves the dip-coating of TiO₂ ETL and perovskite light absorbing layer, the spin-coating of spiro-MeOTAD hole-transport layer (HTL) and the evaporation of Ag as back electrode. Mixed halide perovskite CH₃NH₃PbI_3-xCl_x is chosen as the perovskite light absorber and one-step dip-coating process combined with time-temperature dependent annealing treatment was adopted to deposit the

Conclusions

In conclusion, a very simple and fast dip-coating process was investigated as a promising means of solution-coating of TiO₂ ETLs and perovskite films free of pinholes for efficient, reproducible, and potential large-area P-PH PVKSCs. The solution-saving dip-coating method greatly minimizes the waste of source materials enabling fast and easy production of uniform thin films. The resultant highly compact TiO₂ ETLs with efficient hole-blocking and smooth perovskite films with high surface

Acknowledgements

This work was supported by National Natural Science Foundation of China (Grant Nos. 61377031, 61504068). Also, the author L.K. Huang would like to thank the sponsored by the 2016 Doctoral Student Innovation Project in Nankai University.

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Efficient and hysteresis-less pseudo-planar heterojunction perovskite solar cells fabricated by a facile and solution-saving one-step dip-coating method

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Results and discussion

Conclusions

Acknowledgements

Thin Solid Films

Chem. Eng. Sci.

Thin Solid Films

Sol. Energy Mater. Sol. Cells

J. Am. Chem. Soc.

Nanoscale

Science

Science

Nat. Nanotechnol.

Science

Science

J. Phys. Chem. Lett.

J. Mater. Chem. A

Phys. Chem. Chem. Phys.

Adv. Energy Mater.

J. Mater. Chem. A

Energy Environ. Sci.

Nanoscale

Chem. Commun.

Phys. Chem. Chem. Phys.