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UBC Theses and Dissertations

The design of hole-transport materials to stabilize the performance of perovskite solar cells Chiykowski, Valerie Anne


Over six decades of photovoltaic research have led to the emergence of a highly efficient technology called perovskite solar cells (PSCs). Despite the recent sharp rise in power conversion efficiencies (PCEs) of this technology, PSCs have not yet been deployed at scale owing in part to the unsatisfactory stability of devices. The stability issues are due to the light absorbing layers being susceptible to dissolution and the hole-transport material (HTM) layers undergoing morphological changes under real life conditions. This dissertation seeks to suppress mechanisms of PSC degradation through the design of HTMs. I designed a series of five structurally similar HTMs to study the effect of triphenylamine (TPA) location and number on the thermal stability (i.e., glass transition temperature, Tg) of the HTM layer. My studies demonstrate that where the TPA units are positioned about a spiro-carbon core can shift the Tg upwards of 30 °C. I designed HTMs that can be electrochemically and thermally polymerized to yield an encapsulation layer for the PSC. I demonstrated that the polymerized HTM layer decreases film wettability and can be incorporated into a PSC device. I interrogated a series of three structurally analogous donor-acceptor (D-A) architectures (i.e., monopodal, bipodal and tripodal architectures) to determine the role of molecular structure on the hole mobility of HTMs. From these experiments, I learned that “monopodal” D-A architectures yielded the highest hole mobilities because of the low computed reorganization energy, small polaron stabilization energy and hole extraction potential associated with this HTM. Overall, I demonstrated three mechanisms to suppress either the degradation of the photoactive perovskite layer, the morphological changes to the HTM layer or the instability caused by additives in HTM films. I suggest future design principles to yield stable PSC devices towards the commercialization of this technology.

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