Centimetre scale mesoscopic perovskite solar cells via a novel combined solid state-solution crystallisation method

Regardless of architecture, most of the high efficiency Perovskite Solar Cells (PSCs) reported to date have sizes less than 0.1 cm2 [1] whereas an obligatory minimum area of 1-2 cm2 is recommended, to allow a comparison of competing technologies of photovoltaic cells [2]. A two-step solution based process is widely adopted for the growth of perovskite in small area high efficiency PSCs, whereby an initial lead iodide layer is spin coated on the electron/hole collection layer. The substrate is subsequently immersed/spin coated with methyl ammonium salt (MAI) solution prior to annealing at ~70 0C to form the perovskite [3]. The scalability of this approach is severely limited due to poor coverage of perovskite layer which often results in inferior cell efficiency. The best centimetre-scale PSCs reported to date are by vacuum evaporation method [4] and modified two step approach [5] (where lead iodide coated substrate is inserted into a pre-heated metal enclosure containing MAI powder to form the perovskite) with efficiencies of 10.9 to 12.6% respectively. Replacing the conventional hole and electron transport layers with doped inorganic oxide materials to minimise hysteresis has resulted in the highest efficiency of 15% on an area of ~1cm2 so far [1]. Here, a large area compatible combined solid state- solution crystallisation process is proposed for the first time. The new method gives better uniformity and pin-hole free coverage in comparison to the conventional solution based process.