Development and Optimisation of Efficient Spray-Coated Perovskite Solar Cells

In recent years lead halide perovskites have emerged as a promising photovoltaic material with over 20% power conversion efficiency (PCE) demonstrated. Typically, these devices are fabricated on small areas (less than 1 cm2) utilising spin coating, a technique which is not industrially compatible. Here we demonstrate techniques that can produce efficient perovskite solar cells (PSCs) utilising ultrasonic spray-coating. Spray-coating is a method widely used in industry for coating large areas at speed. A method to sequentially deposit all solution processed layers in a normal architecture PSC is developed. Here compact-TiO2, mesoporous-TiO2, CH3NH3PbI(3-x)Clx perovskite and doped spiro-OMeTAD layers are deposited in ambient conditions utilising an ultrasonic spray-coater, achieving a peak PCE of 10.2% on small area devices. The average PCE of the spray-cast devices (9.2%) compares favourably with spin coated references (11.4%). This process is then applied to larger substrates to create a 6.6% efficient device with an active-area of 1.5 cm2. This PCE value was independently verified at the Centre for Renewable Energy Systems Technology (CREST). Higher efficiency spray-cast PSCs are fabricated by utilising a glovebox mounted spray-coater and vacuum assisted solution processing (VASP). In addition, a higher performance “triple-cation” perovskite formulation with the composition Cs0.05FA0.81MA0.14PbI2.55Br0.45 is utilised. By exposing the wet precursor film to a low vacuum immediately after deposition the solvent is rapidly extracted from the film enhancing nucleation. This results in smoother and more uniform perovskite layers compared to films that are simply annealed after spray-deposition. When incorporated into a PSC these VASP treated thin films enable devices with a peak PCE of 17.8%. This vacuum assisted spray method is then combined with ambient ultrasonic spray-coating of tin oxide nanoparticles and spiro-OMeTAD. The use of spray-deposition allows the rapid coating of 25 x 75 mm substrates which can then be utilised to form a series of 15.4 mm2 PSCs with an average PCE of 12.2% and a peak efficiency of 15.1%. This demonstrates the flexibility of spray-deposition and is an important proof of concept for potential industrial development of spray-coated PSCs.