High-Quality ITO/Al-ZnO/n-Si Heterostructures with Junction Engineering for Improved Photovoltaic Performance

A heterostructure of Sn-doped In2O3 (ITO)/Al-doped ZnO (AZO)/n-Si was proposed and studied for photovoltaics. The top ITO worked as a transparent conducting layer for excellent optical transparency and current collection. The AZO/n-Si served as the active junction and provided the built-in potential (qVbi) for the photovoltaic devices. To achieve a higher open circuit voltage (Voc), which is the main challenge for AZO/Si heterojunctions due to the junction interfacial defects, the AZO and AZO/Si junction properties were systematically investigated. By modulating the Al doping in the AZO thin films via a dual beam co-sputtering technique, the AZO/n-Si junction quality was significantly improved with qVbi increased from 0.21 eV to 0.74 eV. As a result, the Voc of our best device was enhanced from 0.14 V to 0.42 V, with a short circuit current (Jsc) of 26.04 mA/cm2 and a conversion efficiency (Eff) of 5.03%. To our best knowledge, this is the highest Voc reported for ZnO/Si heterojunctions prepared by the sputtering method. The results confirmed the validity of our proposed structure and junction engineering approach and provided new insights and opportunities for ZnO/Si heterojunction optoelectronics.