Reducing Interfacial Losses in Perovskite Solar Cells

McCarthy, Declan Patrick

Graduate Thesis Or Dissertation

Reducing Interfacial Losses in Perovskite Solar Cells Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/9019s400f

Abstract

Metal-halide perovskites possess an unprecedented combination of electronic and optical properties resembling those of traditional inorganic semiconductors yet can be processed at low temperatures from solution. Additionally, these materials have short estimated energy payback times and high potential for integration into tandem-on-silicon solar cells. The latest record single junction perovskite solar cell has reached a certified efficiency of 25.8% and perovskitesilicon tandem solar cells have reached an efficiency of 33.7%. Nevertheless, numerous research challenges remain towards commercialization, including efficiency, stability, scalability, and Pb toxicity. The research within this thesis focuses on a materials driven approach to reduce nonradiative losses in perovskite photovoltaics for single junction and tandem-on-silicon applications.

I will first describe the synthesis, characterization, and material properties an NDI side chain copolymer incorporating cinnamate crosslinking groups. We demonstrate the polymer’s high transparency, thermal stability, photocrosslinking, and n-doping via solution and sequential processes. We implement this polymer in PSCs and characterize its solar-cell device performance relative to an uncrosslinked homopolymeric counterpart in n-i-p devices with a MA-free perovskite absorber. Next, I will discuss a large photoluminescence-based screening of passivation materials. Candidate passivators were screened across a variety of perovskite compositions. A benzylammonium trifluoromethanesulfonate salt, BAOTf, was identified as a highly effective passivation molecule, allowing for the fabrication of solar cells exhibiting very low hysteresis with PCEs >19% with a MA-free mixed-cation mixed-halide perovskite absorber (Cs17Br25). Finally, the reactivity of amines and ammoniums with formamidinium salts was explored. Understanding solution reactivity of amines with formamidinium salts enabled the synthesis, isolation, and implementation of the product(s) formed in these reactions as additives and surface passivation agents in perovskites. This work helped to elucidate the role of the amine/ammonium additives in controlling FA-containing perovskite growth and crystallization processes.

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