Mixed‐Organic‐Cation Perovskite Photovoltaics for Enhanced Solar‐Light Harvesting

Hybrid organic–inorganic lead halide perovskite APbX 3 pigments, such as methylammonium lead iodide, have recently emerged as excellent light harvesters in solid‐state mesoscopic solar cells. An important target for the further improvement of the performance of perovskite‐based photovoltaics is to extend their optical‐absorption onset further into the red to enhance solar‐light harvesting. Herein, we show that this goal can be reached by using a mixture of formamidinium (HN=CHNH 3 + , FA) and methylammonium (CH 3 NH 3 + , MA) cations in the A position of the APbI 3 perovskite structure. This combination leads to an enhanced short‐circuit current and thus superior devices to those based on only CH 3 NH 3 + . This concept has not been applied previously in perovskite‐based solar cells. It shows great potential as a versatile tool to tune the structural, electrical, and optoelectronic properties of the light‐harvesting materials.