Role of Formamidinium (FA) In the Electronic and Thermodynamic Properties of MA(Pb: Sn)I3 Perovskites Using First Principle Calculations

Abstract

Research on perovskite solar cells employing tin to replace or partially replace lead is becoming more popular because of the recent achievement of about 24.2% conversion efficiency for ecologically benign mixed Pb-Sn perovskite solar cells. However, a smaller effect on cohesive energies caused by the addition of a Sn metal has a considerable effect on thermodynamic properties of Pb-Sn perovskites under high-temperature effects. This paper investigates the role of formamidinium in the electronic and thermodynamic properties of MA(Pb: Sn)I₃ perovskite alloy using density functional theory and CASTEP analysis through the Materials Studio. The intended A-cation perovskites have typical compounds FAxMA_1-xSn_0.5Pb_0.5I₃, where x=0, 0.2, 0.4 and 0.6. The control and FA-based perovskites were computed through CASTEP analysis from Material studio to determine the electronic and thermodynamic properties. The findings revealed an improved thermodynamic properties of FA added perovskites compared to control ones whereby no significant effect was found in band gap of MAPb0.5Sn0.5I3 perovskite due to addition of formamidinium. However, when x is above 0.5, the quality of the perovskite films declined, with a wide grain size dispersion and little crystallization as well as the phase impurities were detected. This necessitated a theoretical approach to achieve an optimum amount of FA additive required to improve the properties as well as providing a theoretical guidance for improving the properties of perovskite materials before carrying out experiments. Furthermore, the study predicts that it is possible to create a stable thermal MA(Pb_: Sn)I₃ alloy, if there is a well-thought-out design, which lays a foundation for the development and application of tin-lead mixed perovskite devices.