Date on Master's Thesis/Doctoral Dissertation

5-2024

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Grapperhaus, Craig

Committee Member

Buchanan, Robert

Committee Member

Thompson, Lee

Committee Member

Ramezanipour, Farshid

Committee Member

Druffel, Thad

Author's Keywords

Flexible perovskite solar cell; large area fabrication of perovskite solar cells; perovskite compatible metal oxide electron transport materials; solution processing of SnO2 for inverted perovskite solar cells

Abstract

Over the past decade, perovskite solar cell (PSC) technology has attracted significant attention for its low material costs, simple fabrication processes, and impressive photovoltaic performance, with recent power conversion efficiencies (PCEs) surpassing 26%. This advancement marks PSCs as strong competitors to traditional silicon-based photovoltaics. Despite the high efficiency of PSCs, the path to commercialization is hindered by challenges in stability, scalability, and module efficiency. The stability and scalability of PSCs are primarily dependent on the successive charge transfer layers (CTLs) that are interfaced with the perovskite layer. Among CTLs, metal oxide (MOx) CTLs are preferred for their cost-effectiveness, high stability, and scalability, facilitated by solution processing. Nonetheless, their application is mainly confined to being deposited beneath the perovskite layer due to solvent incompatibility of typical metal oxide dispersion mediums with the perovskite layer and high-temperature requirements to process metal oxide thin films. This dissertation proposes a novel approach for depositing tin (IV) oxide (SnO2) as an electron transport layer (ETL) directly onto the perovskite layer, aiming to fabricate large area, inverted flexible PSCs. SnO2 is recognized for its excellent optoelectronic properties, low-temperature processability, and superior photo and chemical stability, yet its integration into inverted (p-i-n) architectures has been challenging due to solvent incompatibility and high processing temperature demands. We address these challenges by functionalizing pre-synthesized SnO2 nanoparticles with acetate through ligand exchange, allowing their dispersion in anhydrous ethanol and enabling direct blade coating onto the perovskite without damage. The integrity of the perovskite layer after the deposition of the solution processed SnO2 was confirmed through X-ray diffraction and scanning electron microscopy analysis. The resulting SnO2 nanoparticle dispersions performed well as an ETL in inverted perovskite solar cells and demonstrated excellent compatibility with diverse perovskite compositions. Furthermore, the performance of SnO2 as an ETL was enhanced by doping the SnO2 nanoparticles with yttrium during the synthesis process. The yttrium doped SnO2 dispersion significantly improved performance in inverted flexible PSCs. Flexible PSCs on PET-ITO substrates, fabricated using blade coating methods, exhibited a champion PCE of 20.41% with an open-circuit voltage (VOC) of 1.17V for the triple cation perovskite composition. This study highlights the potential of fully solution-processed metal oxide charge transfer materials as a cost-effective and efficient alternative to fullerene-based organic ETLs in inverted perovskite solar cells, leading to efficient large-area flexible PSCs.

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