A Study on the Effects of Mixed Organic Cations on the Structure and Properties in Lead Halide Perovskites
Recently, organic-lead halide perovskite has emerged as a strong competitor in photovoltaic and general optoelectronic applications owing to its remarkable characteristics, including high balance hole and electron mobility, strong absorption coefficient and long carrier lifetime. However, the commercial applicability of these materials is hampered by their relative lack of stability compared to established inorganic and organic semiconductors. It has been found that it is possible to tune the properties and stability of the organic-lead halide perovskite materials by site-substitution at A sites of the ABX3 perovskite structure. Here, organic cations (NH4+, HC (NH2)2+, CH3CH2NH3+) were successfully incorporated in the methylammonium-based perovskite crystal to investigate the role of organic cations on structure, optical features, thermal stability, and electrical transport properties. Powder X-ray diffraction results indicate that size of organic cations can not only cause lattice strain by lattice contraction or dilation but also may induce phase transitions by octahedral tilting. Meanwhile, band gaps of these crystals show organic cations could tune the band gap energy of perovskite by changing the Pb-I bond angle, which agrees with previous reports. The result of thermogravimetric analysis indicates thermal stability is related to the probability of HI formation which is directly related to the acidity of the organic species. The studies and results from this work provide guidance for 3D perovskite crystals applications.