Surface sensitization and modification in hybrid organic-inorganic photovoltaics
Hill, Rebecca B. M.
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Interface optimization is key to the development of next-generation photovoltaic systems such as dye-sensitized (DSSC) and perovskite (PSC) solar cells. In dye-sensitized solar cells, sensitizers have a pivotal role in light absorption, charge generation, and prevention of recombination at an interface. Squaraine sensitizers are a promising class of near-IR absorbing dyes for DSSCs, and the investigation of out-of-plane groups and extended π-conjugation resulted in red-shifting the absorption maxima, preventing dye aggregation, and increasing current. For donor-π-acceptor dyes, a direct comparison of rhodanine-based acceptors with carboxylic acids vs. phosphonic acids as anchors demonstrated the stability of strongly binding phosphonic acids to dye desorption in the electrolyte. In n-i-p lead organo-halide perovskite solar cell devices, the device performance is greatly affected by the electron transport layer and subsequent perovskite crystal formation. Treating C60 with poly(allylamine) resulted in optimized surface energy, work function, and solvent resistance, while increasing power conversion efficiency and retention of device performance relative to the control after 600 bending cycles on a flexible substrate. Phosphonic acid surface modification of ALD-deposited tin oxide electron transport layers yielded modified devices that retained 86% of their initial efficiency under inert atmosphere while the control retained 65%, making phosphonic acid surface modification of interest for the stability of perovskite solar cells under encapsulation. The results in this thesis highlight the significant effects of small structural modifications at surfaces on device efficiency and stability in hybrid organic-inorganic photovoltaics.