Lead-free solid-state organic-inorganic halide perovskite solar cells

Lead-free solution-processed solid-state photovoltaic devices based on methylammonium tin iodide (CH 3 NH 3 SnI 3) perovskite semiconductor as the light harvester are reported. Featuring an optical bandgap of 1.3 eV, the CH 3 NH 3 SnI 3 perovskite material can be incorporated into devices with the organic hole-transport layer spiro-OMeTAD and show an absorption onset at 950 nm, which is significantly redshifted compared with the benchmark CH 3 NH 3 PbI 3 counterpart (1.55 eV). Bandgap engineering was implemented by chemical substitution in the form of CH 3 NH 3 SnI 3-x Br x solid solutions, which can be controllably tuned to cover much of the visible spectrum, thus enabling the realization of lead-free solar cells with an initial power conversion efficiency of 5.73% under simulated full sunlight. Further efficiency enhancements are expected following optimization and a better fundamental understanding of the internal electron dynamics and corresponding interfacial engineering. The reported CH 3 NH 3 SnI 3-x Br x perovskite solar cells represent a step towards the realization of low-cost, environmentally friendly solid-state solar cells.