Roll-to-roll micro-gravure printed large-area zinc oxide thin film as the electron transport layer for solution-processed polymer solar cells

Abstract Large-scale, roll-to-roll (R2R) micro-gravure printing process was developed to deposit the electron transport layer (ETL) using low-temperature, solution-processable zinc oxide (ZnO) nanoparticle ink on flexible substrate for fabricating inverted organic solar cells (OSCs). The properties of micro-gravure R2R printed ZnO thin film was optimized via using web tension, substrate pre-treatment and printing speed, leading to high-quality and thickness controllable ZnO thin films. The inverted OSCs using R2R micro-gravure printed ZnO thin film as the ETL showed performance parameters comparable to those of spin-coated ZnO thin film ETL on the flexible substrate in both P3HT:PCBM and PTB7-Th:PC71BM based devices. The research demonstrated that the potentially commercial large-scale, R2R micro-gravure printing process could be used to produce high-quality ZnO thin film with controllable thickness for efficient inverted OSCs, which would accelerate the development of fully R2R micro-gravure printing OSCs and their commercialization.