Systematic survey of suitable buffer and high resistive window layer materials in CuIn1−xGaxSe2 solar cells by numerical simulations

- Numerical simulations of buffer/window layers based on an experimental CIGS device.
- Device model features: OVC-layer, non-uniform CIGS doping, interface defect.
- Sensitivity analysis on CIGS conduction band edge position χe(CIGS).
- Best: negligible conduction band offset Δχe between CIGS and buffer layer.
- Most suitable buffer and window layer is ZMO(y), y critically depends on χe(CIGS).

This work investigates the impact of opto-electronical buffer (b) and high resistive window layer (w) properties, i.e. band gap Eg(b,w) and electron affinity χe(b,w), on the device performance of chalcopyrite CuIn1−xGaxSe2 (CIGS) solar cells by numerical simulations with SCAPS. We established an initial device model based on an experimental device and its J-V, C-V, and EQE data at room temperature as well as its quantified depth profile for the [Ga]/([Ga]+[In]) ratio (GGI). The device features a non-uniform CIGS doping profile as well as a strongly doped CIGS surface layer. Based on our simulations that include various buffer layer materials, we argue that the most suitable buffer and window layer is Zn1−zMgzO. The potential gain in efficiency is up to 0.9% absolute which corresponds to a relative gain of 4.1%.

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