Abstract: Transparent conductive oxide (TCO)-based ultra-thin Cu (In, Ga) Se₂ (CIGSe) solar cell have the potential for building photovoltaic integration. However, due to the presence of a back Schottky junction, increasing the back recombination rate S_b not only improves hole transport but also increases photo generated electron back recombination, thereby suppressing its performance improvement. This article uses 1D-SCAPS software to theoretically explore how back interface nanophotonic structures (NPs) can improve the performance of cells. The research results indicate that the introduction of back interface NPs generates complex electrical effects. On the one hand, NPs themselves do not absorb light energy, thereby reducing the effective light absorption volume near the back interface, resulting in a decrease in the concentration of photogenerated carriers at the back interface and a significant decrease in back recombination of back interface. On the other hand, the introduction of NPs increases the thickness of the absorption layer, causing the space charge region (SCR) to move away from back interface, reducing its collection efficiency for photo generated electrons and leading to an increase in back recombination. At a high back recombination rate (S_b=1.0×10⁷ cm·s^-1), the decrease in photogenerated carrier concentration leads to a greater decrease in back recombination than the increase in back recombination caused by SCR movement, resulting in an overall decrease in back recombination. At the same time, the reduction of back recombination also alleviates the photogenerated electron loss at high S_b, thereby relieving the inhibition of back recombination on battery performance that increases with S_b. These findings provide reference for the design and optimization of TCO-based ultra-thin CIGSe solar cell.

Key words: TCO-based ultra-thin CIGSe solar cell, nanophotonic structure, schottky barrier, light absorption, back recombination, transparent conductive oxide