High Efficiency and High Open Circuit Voltage in Quasi 2D Perovskite Based Solar Cells

An important property of hybrid layered perovskite is the possibility to reduce its dimensionality to provide wider band gap and better stability. In this work, 2D perovskite of the structure (PEA)₂(MA)_{n –1}Pb_nBr_{3 n +1} has been sensitized, where PEA is phenyl ethyl-ammonium, MA is methyl-ammonium, and using only bromide as the halide. The number of the perovskite layers has been varied (n) from n = 1 through n = ∞. Optical and physical characterization verify the layered structure and the increase in the band gap. The photovoltaic performance shows higher open circuit voltage (V_oc) for the quasi 2D perovskite (i.e., n = 40, 50, 60) compared to the 3D perovskite. V_oc of 1.3 V without hole transport material (HTM) and V_oc of 1.46 V using HTM have been demonstrated, with corresponding efficiency of 6.3% and 8.5%, among the highest reported. The lower mobility and transport in the quasi 2D perovskites have been proved effective to gain high V_oc with high efficiency, further supported by ab initio calculations and charge extraction measurements. Bromide is the only halide used in these quasi 2D perovskites, as mixing halides have recently revealed instability of the perovskite structure. These quasi 2D materials are promising candidates for use in optoelectronic applications that simultaneously require high voltage and high efficiency.