β-cyclodextrin–polyacryloyl hydrazide-based surface modification for efficient electron-collecting electrodes of indoor organic photovoltaics

Abstract

Indoor organic photovoltaics (OPVs) show immense potential as a reliable energy harvester for powering emerging Internet of Things devices because of their unique optoelectrical properties. The extremely low number of charge carriers under indoor lighting conditions in comparison to 1-sun conditions necessitates different techniques to optimize the performance of indoor OPVs. In this study, an indium tin oxide (ITO) surface was modified using a water-soluble β-cyclodextrin–polyacryloyl hydrazide (CD–PAH). The abundant amine functional groups on the polyacryloyl hydrazide arms induce a vacuum-level shift owing to their excellent electron-withdrawing ability. Consequently, the work function (WF) of ITO decreased from 4.5 to 4.1 eV, providing a suitable energy-level alignment between ITO and the photoactive layer. The photovoltaic performance of inverted poly(3-hexylthiophene):indene-C60 bisadduct-based OPVs with the surface-treated ITO was evaluated under various lighting conditions. The average power conversion efficiency of the optimized OPV increased substantially from 1.2 ± 0.1% to 3.5 ± 0.1% under 1 sun illumination and 2.4 ± 0.2% to 8.1 ± 0.4% under light-emitting diode illumination. This remarkable performance improvement can be attributed to the excellent transmittance, smooth surface morphology, and suitable WF of the surface-modified ITO.

Keywords

• Indoor organic photovoltaics
• Surface modification
• Cyclodextrin–polyacryloyl hydrazide (CD–PAH)
• Electron-collecting electrode