Rear-Passivated Ultrathin Cu(In,Ga)Se2 Films by Al2O3 Nanostructures Using Glancing Angle Deposition Toward Photovoltaic Devices with Enhanced Efficiency

In this work, for the first time, the addition of aluminum oxide nanostructures (Al2O3 NSs) grown by glancing angle deposition (GLAD) is investigated on an ultrathin Cu(In,Ga)Se-2 device (400 nm) fabricated using a sequential process, i.e., post-selenization of the metallic precursor layer. The most striking observation to emerge from this study is the alleviation of phase separation after adding the Al2O3 NSs with improved Se diffusion into the non-uniformed metallic precursor due to the surface roughness resulting from the Al2O3 NSs. In addition, the raised Na concentration at the rear surface can be attributed to the increased diffusion of Na ion facilitated by Al2O3 NSs. The coverage and thickness of the Al2O3 NSs significantly affects the cell performance because of an increase in shunt resistance associated with the formation of Na2SeX and phase separation. The passivation effect attributed to the Al2O3 NSs is well studied using the bias-EQE measurement and J-V characteristics under dark and illuminated conditions. With the optimization of the Al2O3 NSs, the remarkable enhancement in the cell performance occurs, exhibiting a power conversion efficiency increase from 2.83% to 5.33%, demonstrating a promising method for improving ultrathin Cu(In,Ga)Se-2 devices, and providing significant opportunities for further applications.