Investigating Bismuth-based Perovskite Solar Cells

University of Minnesota M.S. thesis. December 2019. Major: Chemical Engineering. Advisor: Zhihua Xu. 1 computer file (PDF); 65 pages.Solar Cells are one of the most prominent alternatives for fossil fuels. In recent years perovskite solar cells has gained a lot of attention due to its high photovoltaic performance, low cost and the ease of fabrication. However, one of the drawbacks of perovskite solar cells is the toxic constituent element lead (Pb) in the perovskite structure in the form of ABX3, e.g. methylammonium lead iodide (CH3NH3PbI3). To find an alternative to replace lead (Pb) without changing the established perovskite structure, bismuth (Bi) was investigated on the basis of split-ion approach where a three-layer (Bi2Te2, BiI3, and CH3NH3I) deposition process was formulated to fabricate perovskite structure in the form of CH3NH3BiTeI2. Our novelty resides in a unified approach of studying bismuth telluride as a possible compound which would react with bismuth iodide and then having a three-layer deposition method with methylammonium iodide to form a single crystal structure. The solar cells based on the novel lead-free perovskite material have a power conversion efficiency of 0.06%, open-circuit voltage of 0.46 V and current density of 0.38 mA/cm2. Absorption spectrum were used to identify the optimal annealing temperatures to form the perovskite structure. X-ray diffraction showed few peaks matching to the lead-based perovskite CH3NH3PbI3, which suggests the tetragonal perovskite structure was partially formed. The compositional gradient existing in the thermal evaporated Bi2Te3 thin film might be the major culprit leading to the incomplete formation of perovskite structure