Highly stable and efficient perovskite solar cells passivated by a functional amorphous layer

Perovskite solar cells (PSCs) have shown great potential as a next generation photovoltaic candidate due to the low cost and high efficiency of the devices. However, the ionic and polycrystalline natures of perovskite films lead to high defect densities deteriorating device stability and efficiency, which impedes the practical applications of PSCs. Here, we introduce a novel passivation concept which employs a functional amorphous 5-sulfosalicylic acid (5-SSA)/PbI2 layer with COO− and SO3− groups to suppress defects of under-coordinated Pb2+ ions and iodide vacancies at grain boundaries/surfaces of MAPbI3 films. Furthermore, we find that the amorphous phase can lead to the enlargement of grain size, passivation of defects and suppression of ion migration in the as-deposited perovskite films. Consequently, the 5-SSA/PbI2-modified MAPbI3 devices exhibit efficiencies up to 21.47% and 21.02% on rigid and flexible substrates, respectively. Moreover, the shelf life (3000 h in air with low humidity) and thermal stability (500 h at 60 °C in N2) have been significantly improved. This work provides a promising strategy for overcoming the inherent instability of perovskite films in optoelectronic applications.