Solvent-Dependent Charge Transfer Dynamics under Indoor Light in Efficient and Stable Copper-Mediated DSSCs

Abstract

Indoor photovoltaics (iPVs) are emerging as a sustainable and reliable power source to address the growing energy demands caused by the rapid expansion of the Internet of Things ecosystem. Combining high photovoltaic performance under indoor light with low-cost, simple production, and pleasant aesthetics, copper-mediated monolithic dye-sensitized solar cells (DSSCs) are a strong candidate for iPVs. Efforts have been made to replace expensive and scarce materials used in the preparation of conventional DSSCs with more abundant and sustainable materials. However, DSSCs still employ materials with considerable toxicity, namely, the nitrile-based solvents in the electrolyte solutions. This work considers for the first time propylene carbonate (PC), gamma-butyrolactone (GBL), and N-methyl-2-pyrrolidone (NMP) as candidates for the electrolyte solvent in indoor DSSCs. Among them, PC-DSSCs display power conversion efficiencies (PCEs) competitive with those of 3-methoxypropionitrile-based devices under light intensities between 300 and 1000 lx; both are able to maintain PCEs above 25%. Time-resolved photoluminescence measurements reveal a clear electrolyte donor number-dependent modulation of interfacial electron injection and radiative relaxation dynamics from excited states, which correlates with device performance under weak indoor light. Among other solvents, this study demonstrates PC as a safe, sustainable electrolyte solvent for efficient and stable indoor DSSCs.