Tunable size and sensitization of ZnO nanoarrays as electron transport layers for enhancing photocurrent of photovoltaic devices

Abstract

Tunable size ZnO nanoarrays (NAs) sensitized with CdS, Ag₂S, CdS/Ag₂S quantum dots and solution processed 2-(2-(2-methoxyethoxy) ethoxy) ethyl undec-10-enyl malonate (EEMC) fullerenes have been developed as electron transport layers for improving polymer solar cells performance. ZnO NAs could provide direct and ordered electron channels for electron transportation. The optimized thickness of ZnO NAs was determined by means of contrast experiments with P3HT:PC₆₁BM active layers. CdS, Ag₂S shell and CdS/Ag₂S double-shells could passivate the surface defects of ZnO NAs, increase the electron mobility and enhance light absorption. Moreover, EEMC assists the infiltration of the active layer into inorganic nanoarrays. Consequently, the performance of the inverted device based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7):[6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) with ZnO/CdS/Ag₂S/EEMC core/multi-shells NAs as electron transport layer has been greatly improved to 7.7% with a high short-circuit current density of 17.9 mA cm⁻². Moreover, the fabrication process was low-cost and environment-friendly, which would be in favor of a large-scale production of polymer solar cells.