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Lead–halide-based hybrid organic–inorganic perovskite materials (APbX3) have recently garnered increased attention among researchers worldwide as promising thin-film photovoltaic materials. Laboratory-scale solar cells incorporating APbX3 materials as the light absorber have demonstrated impressive efficiencies of > 20%, but commercialization of solar cells based on solution-cast materials and with only low-temperature processing steps is in-part limited by toxicity and instability of the photoactive materials even under ambient conditions. Specifically, APbX3 contains toxic lead and is not stable in ambient conditions in part because AX dissociates into two water-soluble, low-boiling point species.

Therefore, the goal of my doctoral thesis project was to replace the organic monocationic salts in perovskite materials with non-volatile and less water-soluble analogs in the form of organic dicationic salts. Using this rationale, I have demonstrated the use of novel perovskite-like bismuth–halide and copper–halide materials as the photoactive layer in solar cells, which contain hexanediammonium dications (HDA2+) that serve as the organic crystal fastener. I have elucidated structure–property relationships of these and related materials with different organic linkers through measurement of crystal structure, powder and thin-film characterization of the materials, and long-term thermal and moisture stability. I have also studied these materials using ultrafast spectroscopy techniques to elucidate energy-transport and charge-transport dynamics of these materials as thin films. Efficient photovoltaic devices featuring a dicationic metal–halide material that does not contain lead may offer a more environmentally-friendly, stable alternative to the APbX3 photovoltaic devices that currently dominate emerging photovoltaic technology research.

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