Micro-cavity–induced optical resonance for performance enhancement in ultra-thin CdTe photovoltaic devices

This study proposes a micro-cavity architecture based on the optical resonance principle to enhance photon harvesting and minimize efficiency losses due to thinning in ultra-thin CdTe-based solar cells. The cavity-free reference structure has been optimized both optically and electrically using the Transfer Matrix Method and SCAPS-1D simulations. The results revealed that a 240 nm CdTe layer provides the optimal balance between high optical absorption and efficient carrier transport. The micro-cavity structure was realized by employing a SnO₂/Au/WO₃ multilayer system as a dielectric/metal/dielectric resonator at the bottom interface. This configuration strengthened the electromagnetic field within the active CdTe layer, producing distinct resonance modes in the visible and near-infrared regions. As a result, the optical path length of photons increased, the average visible reflectance decreased, and photon harvesting was improved by approximately 9% under resonance conditions. Ultimately, micro-cavity integration enabled the preservation of photovoltaic performance while reducing the CdTe absorber thickness by half. This approach offers an innovative light-management strategy that balances high efficiency and low material consumption in ultra-thin film photovoltaics, establishing a strong roadmap for future semi-transparent and tandem solar cell designs.