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

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com (1 of 7) 1604733 configuration is of the structure R2(CH3NH3)n–1MnX3n+1, where R is an organic group, M is a divalent metal, and X is a halide (Cl−, Br−, or I−). The number of perovskite layers are determined by the long organic groups separated by the MX6 layers.[8] In this work, quasi 2D perovskites were synthesized which could involve a mixing of 2D and 3D perovskite in the same film. When reducing dimensionality, the exciton binding energy increased up to 300 meV for typical 2D organic–inorganic perovskite; in addition, the excitons are expected to be more stable in low dimension perovskites. This family of materials permits tuning of optical and electrical properties by changing either the organic or the inorganic component, or their relative abundance. There are two main options to tune the organic–inorganic perovskite band gap: (i) Creating a confinement in the perovskite structure, such as reducing dimensionality. When moving from pure 3D perovskite to 2D perovskite, the band gap increases. (ii) Changing the halides in the perovskite structure to bromide to increase the perovskite band gap.[9] Cao et al. used the butylammonium as the barrier to create low dimensional perovskites using the iodide as the halide starting from n = 1 (single perovskite layer) to n = 4; however, the photovoltaic (PV) performance of these cells was low, mainly due to transport problems.[10] Quan et al. fabricated reduced dimensionality in the perovskite structure using the iodide as well, where low n values and high n values were studied. It was shown that the high n values could provide better stability than the 3D perovskite.[11] Several studies show the use of 3D perovskite based bromide in high voltage cells having open circuit voltage ranging from 1.15–1.5 V.[12–17] Moreover, high voltage (1.4 V) and high efficiency (6.7%) were reported with hole transport material (HTM) based on tri-arylamine polymer derivatives containing fluorene and indenofluorene.[18] High voltage was also observed for cells without a hole conductor; however, the efficiency was still low.[19,20] Recently, MAPbBr3 perovskite with more than 10% efficiency was reported for planar configuration.[21] In this work, we demonstrate the combination of the two effects that increase the perovskite band gap, i.e., reduced dimensionality and use of bromide in the perovskite structure. Quasi 2D perovskite (high n values) from the structure High Efficiency and High Open Circuit Voltage in Quasi 2D Perovskite Based Solar Cells