Exploring the Potential of Silicon Clathrate Films with NiOx-Based Selective Contacts for Optoelectronic Devices

Abstract

Silicon clathrates are a unique class of materials with a cage-like structure that offer significant advantages for optoelectronic applications, particularly in indoor photovoltaics (IPV). Their direct bandgaps and tunable electronic properties from metal-like to semiconductor-like behavior enable a wide range of optoelectronic functionalities. In this study, a photovoltaic device is demonstrated based on semiconducting silicon clathrate films (SCF) synthesized from crystalline silicon (c-Si) wafers, with NiOx incorporated as hole selective contact. XPS and Auger spectroscopy confirmed the incorporation of Na within the SCF framework, in agreement with the type-II clathrate structure revealed by XRD analysis. Optical and electronic measurements indicate that the SCF exhibits intrinsic-like behavior with a bandgap of 1.72 eV. Integration of SCF with NiOx resulted in rectification and a clear photovoltaic response under illumination, confirming device functionality. Band alignment analysis suggested efficient hole transport and secondary charge generation from the c-Si substrate. These results highlight the importance of selective contact engineering for efficient charge extraction and demonstrate the potential for further optimization of SCF photovoltaic devices.