Inverted bulk-heterojunction polymer solar cells using a sputter-deposited Al-doped ZnO electron transport layer

In this study, we realized an inverted polymer solar cell by depositing Al-doped ZnO (AZO) through room temperature radio-frequency magnetron sputtering as an electron transport layer (ETL) between an organic PTB7 and PC71BM mixture active layer and indium tin oxide (ITO) transparent electrode. The crystal structure of the AZO thin films changed as the Ar gas pressure was varied. X-ray diffraction showed that the highest crystallinity was obtained at 70 mTorr. Further experiments were carried out to determine the optimum thickness. An AZO film deposited on a glass substrate with a thickness of 100 nm had an average visible-light transmittance of 83.3% and an electrical resistivity of 6.6 x 10(-3)Omega.cm. The power conversion efficiency (PCE) showed no significant difference with regard to thickness, and ranged from of 7% to 8%. The 100-nm AZO thin film had the highest PCE of 7.87%, which is approximately 90% higher than that of the sample without an ETL. (C) 2018 Elsevier B.V. All rights reserved.