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Quantifying doping of hole-transport materials in solid-state solar cells Forward, Rebecka

Abstract

Solid-state dye-sensitized solar cells (ssDSSCs) convert renewable solar energy into electricity by separating electrons and holes. This function of charge separation is achieved by two fundamental layers: the hole transport material (HTM) and the electron transport layer (ETL). The poor stability and reproducibility of these layers is a current impediment to the commercialization of this technology. Doped-HTMs in particular suffer from poor reproducibility due to atmospheric conditions affecting doping, and in many cases, unnecessarily large amounts of dopants are added leading to reduced stability. These issues stem from a lack of a standardized protocol for HTM doping in lab-scale research. I developed a standard protocol to quantify the effective doping of HTMs to increase reproducibility and stability. I demonstrate this technique with state-of-the-art HTM 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro) and indirect oxidant lithium bis (trifluoromethylsulfonyl)imide (LiTFSI). This technique can be extended to quantify the effective doping of other HTM/dopant combinations which will enable optimized doping for ssDSSCs. I fabricated ssDSSCs with varied component composition, device architectures, and material deposition methods to understand the roles of different TiO₂ ETLs and their effects on power conversion efficiency (PCE). The PCE increased with the addition of a compact-TiO2 blocking layer which obstructs deleterious electron recombination pathways. Moreover, it was discovered that the use of TiO₂ clusters as an interlayer and the compact-TiO₂ have a synergistic improvement on PCE. Overall, I demonstrated the optimization of TiO₂ layers and quantified HTM oxidation to improve solid-state solar cell technologies. I suggest future experiments to develop our understanding of dopants and the necessary processing conditions to obtain stable high efficiency solid-state solar cells.

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