Zinc Oxide in Solar Cells: A Comprehensive Review on Its Dual Role as an Emitter and Antireflection Layer

Zinc oxide (ZnO) has emerged as a multifunctional material in solar cell applications due to its high transmittance in the visible range, wide bandgap, and excellent electrical conductivity. This review provides a comprehensive evaluation of ZnO’s dual role as an emitter and antireflection layer, highlighting the technical strategies for enhancing its performance and the challenges faced in advanced solar cell architectures. As an emitter layer, ZnO facilitates effective charge separation and transport, which can be further optimized through strategic doping and interface engineering. High refractive index of ZnO thin films further enables it to act as an efficient antireflection coating, reducing light loss and enhancing photon absorption in the underlying absorber layers. However, achieving optimal interfaces with various absorber materials and scaling up ZnO layers present technical and cost-related challenges. Notable conversion efficiencies of 14%, 19.7%, and 17.9% have been demonstrated for ZnO/p-Si, ZnO/p-GaAs, and ZnO/p-CdTe heterojunction solar cells, respectively. Furthermore, several solar cell structures have shown significant improvements in photovoltaic performance when ZnO is used as an antireflection coating compared to uncoated structures.