Environmentally friendly approach via solvent-free processed perovskite solar cells

Perovskite solar cells have been rapidly developed owning to their simple fabrication procedures, low cost and high efficiency. Currently, record efficiency of perovskite solar cells on rigid substrates exceeds 20%. In general, solution process is used to synthesis the perovskite layer, i.e. MAPbI3. Although solution process is direct and simple, significant usage of organic solvent like chlorobenzene, which is used as anti-solvent during one-step solution process, is not environmentally friendly. In addition, solution processing at low temperatures results in small average grain sizes and poor crystallinity. Furthermore, the film morphology and properties are strongly dependent on fabrication conditions, and the presence of solvent vapor in the glovebox can significantly affect the repeatability and the reproducibility of the perovskite film properties, and consequently the solar cell performance. Thus, it is desirable to develop solvent-free process for the preparation of the perovskite film, different from vapour-deposition processes which would increase perovskite fabrication cost. Such a solvent-free processed perovskite film may lead to not only better efficiency with better film quality, but also more reproducible and greener fabrication process. Approaches of using solid state reaction between PbI2 and MAI will be focused to fabricate MAPbI3 films. After optimization of the solvent-free fabrication process, solar devices for both solvent-free and solution processed were fabricated for efficiency comparison.