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 × 10⁻³ Ω·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.