Researchers at Shanghai Jiao Tong University in China and the Swiss Federal Institute of Technology have reported the development of a new technique to deposit high-quality large-area perovskite films that does not require solvents or vacuum processing. The method reportedly produces homogeneous films with relatively few defects, which leads to an efficiency of 12.1% for a solar module made from a methylammonium lead halide film that is just over 36 cm2 in size.
The research team has developed a new technique to produce large-area methylammonium lead halide (CH3NH3PbI3) perovskite films that relies on rapidly converting amine complex precursors (CH3NH3IÂ·mCH3NH2 (where m is close to 3) and PbI2Â·nCH3NH2 (where n is close to 1) to perovskite films and then applying pressure to them.
The deposited films are free of pinholes and are highly uniform, say the researchers. 'Our technique has the advantage that it does not require any toxic or irritating solvents like N,N-dimethylformamide, dimethyl sulphoxide (DMSO) or gamma-butyrolactone, unlike conventional methods to produce these cells'. 'It does not produce any waste either and no thermal annealing is required. The technique also works in air and at low temperatures, making it more cost-friendly and environmentally friendly overall".
Furthermore, the pressure-processing step at the end is better than the spin-coating method that is widely employed for depositing perovskite films, according to the team.
The film produced by the new technique is highly uniform over a large area (36.1 cm2) with only a 2% variation in film thickness and the grains in the material are around 0.8-1.0 microns in size, which is three to four times bigger than those in spin-coated processed film. The researchers succeeded in making a photovoltaic module with a PCE of 12.1% from such a film.
According to the researchers, the technique will be useful for growing perovskite crystals, which could greatly reduce so-called trap states and further enhance the photovoltaic performance of these materials. 'It could be then used to produce low-cost optoelectronics devices, like light-emitting diodes or laser diodes on a large scale'.