The most effective semiconductors used as absorber layers for solar cells have concerns regarding high capital expenditure (CapEx) for new manufacturing facilities, earth abundance, toxicity, or cost-volatility of the materials. Solution processing is a low cost, low temperature development method leading to lower CapEx. The exploration of new photovoltaic materials seeks to develop an earth abundant, non toxic semiconductor via solution processing with efficiencies comparable to materials like silicon or CdTe. Bismuth rudorffites (chemical formula A_aBi_bX_a+3b) are an interesting category of new materials, proven to be solution processable, to have high absorption, and to be capable of cell efficiencies over 4%. My project seeks to optimize the thin-film morphology and the open circuit voltage (V_oc) of bismuth rudorffite layers, both of which are crucial to achieving high efficiencies. A good morphology will be phase-pure and densely packed, with large grains. By determining the effects of each parameter of the thin-film deposition process (spin-coating, in our case) through Scanning-Electron Microscope imaging and X-Ray Diffractometry, I have determined an optimized deposition procedure leading to good morphology. The utilization of Absolute Intensity Photoluminescence techniques (AIPL) allows for prediction of the V_oc to a high degree of precision without building an entire solar cell, instead only measuring the absorber layer. By illuminating the absorber and detecting the re-emitted light, models can determine the density of "radiative recombinations" of electrons and holes, which correspond to electrons that would be capable of generating a voltage and providing electrical power. By using this method and by building an understanding of rudorffite crystal growth, I have attempted to reduce "non-radiative recombinations," increasing the PL and hence increasing the capacity for high V_oc in rudorffite cells. Here is presented current data, results, and recommended experiments necessary for rudorffites to be a successful photovoltaic material.

BiI₃ is a nontoxic and relatively abundant material with a bandgap of ~1.8eV that displays promising photovoltaic properties. However, BiI₃ solar cells have not reached efficiencies of greater than 1%. One of the major problems is the existence of deep defects in the materials which serve as trap states and increase non-radiative recombination. Here, defect engineering by both isoelectronic and non-isoelectronic doping of BiI₃ is studied to reduce the concentration of deep defects and increase the concentration of free charge carriers, aiming to improve the photovoltaic properties of BiI₃ solar cells. To evaluate the effect of dopants on defect passivation in BiI₃ films, photoluminescence and photoconductivity measurement are applied to determine quasi-fermi level splitting (QFLS) and carrier diffusion lengths, respectively. Additionally, dark photoconductivity measurements are used to determine carrier concentration. Preliminary results have shown an increase in QFLS under an iodine rich environment, though not significantly enough to drastically impact BiI₃ solar cell performance. There is much room for further exploration of dopants and their effect on BiI₃. With every dopant tested we learn more about the properties of BiI₃. This work will deepen our understanding of optoelectronic physics and defect chemistry of BiI₃ solar cell materials, optimize the quality of BiI₃ thin films, and increase the efficiency of BiI₃ solar cells.