Roles of Sn content in physical features and charge transportation mechanism of Pb-Sn binary perovskite solar cells

Tin (Sn)-based perovskites are a low-toxic and eco-friendly alternative because of their faster tendency to form inert oxides which have much lower bio-availability than lead-based perovskites. Therefore, at present paper, different properties of Pb-Sn binary pemvskite solar cells (CH3NH3SnxPb1-xI3 [0 <= x <= 1]) were investigated under ambient conditions without the use of encapsulation techniques. For the first time, cauliflower-like morphologies of Sn/Pb mixed perovskites were synthesized and their structural quantitatively analyzed using modified (Monshi) Scherrer (M-Sch) and Williamson-Hall (W-H) methods. The electrical characterization of the cells revealed that incorporating Sn ions into the Pb-based perovskite not only dramatically reduces the carrier density but also from the molar ratio of x = 0.25 to higher values, it converts the electrical conduction behavior from p- to n-type. This effect could be considered as one of the effective factors in reducing the efficiency (eta) of solar cells from 16.83% for CH3NH3PbI3 to 0.86% for CH3NH3SnI3. Therefore, choosing an appropriate strategy against this electrical conductivity behavior could help us to achieve a new approach to reducing the toxicity of perovskite solar cells with the least reduction in their efficiency.