Mixed-organic-cation perovskite photovoltaics for enhanced solar-light harvesting

Abstract

Hybrid organic-inorganic lead halide perovskite APbX3 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=CHNH3+, FA) and methylammonium (CH3NH3+, MA) cations in the A position of the APbI3 perovskite structure. This combination leads to an enhanced short-circuit current and thus superior devices to those based on only CH3NH3+. 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. A productive partnership: Perovskite solar devices with mixed organic cations could outperform the standard methylammonium lead iodide pigment owing to extended light absorption and a higher carrier-diffusion length. Thus, the best optoelectronic features of methylammonium and formamidinium cations were combined in a perovskite solar cell with a striking 14.9 % power-conversion efficiency (red curve: in simulated sunlight; blue curve: in the dark). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.