Author ORCID Identifier

https://orcid.org/0000-0001-6118-6388

Date Available

5-11-2024

Year of Publication

2024

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department/School/Program

Chemistry

First Advisor

Dr. Kenneth R. Graham

Abstract

Metal halide perovskite semiconductors have attracted much interest for various applications, such as solar cells, light emitting diodes, photodetectors, and lasers, due to their excellent optoelectronic properties. Photovoltaic cell development is centered on Pb-based perovskites, which have equal photovoltaic performance compared to the traditional silicon photovoltaic. But concerns arising from the usage of toxic lead metal have motivated the research community to seek an alternative derivative. Among those, tin halide perovskites show much promise as an alternative to Pb-counterparts due to their ideal bandgap for single junction photovoltaics and similar optoelectronic properties to Pb perovskites. Nevertheless, tin perovskites suffer from easy oxidation of Sn2+ and intrinsic p-type doping, which results in poor device performance and stability compared to their Pb-counterparts. To overcome these issues, additive engineering and formation of mixed 2D/3D perovskite phases are widely being investigated.

To select an effective additive, it is important to understand the mechanisms by which these additives act in perovskite precursor solution as well as in thin film to mitigate and stabilize the Sn2+ oxidation. We found that additives stabilize the Sn2+ from oxidation and alleviate the Sn4+ concentration through halide exchange, reducing ability, and antioxidant ability. To further investigate the additives role on electronic and ionic defects, photothermal deflection spectroscopy (PDS), ultraviolet photoemission spectroscopy (UPS) and thermal admittance spectroscopy (TAS) were employed. Our results show that FASnI3 perovskite films with SnF2 as an additive, where SnF2 is a universally used additive in tin halide perovskites, show decreased Sn4+ formation, reduced sub-gap energy states and less ion migration due to the strong Sn-F bond and halide exchange with SnI4 impurities, that help improve photovoltaic device efficiency.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.156

Funding Information

National Science Foundation under cooperative agreement No. 1849213.

U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award Number DE-SC0018208.

National Science Foundation, DMR 2102257

National Science Foundation CHE 2108134

U.S. Department of Energy, Established Program to Support Competitive Research, DE-SC0021283

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