β-cyclodextrin–polyacryloyl hydrazide-based surface modification for efficient electron-collecting electrodes of indoor organic photovoltaics
Sang Hyeon Kim, Chan Hyung Park, Muhammad Ahsan Saeed, Doo‐Hyun Ko, Jung‐Hyun Lee, Jae Won Shim
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.