Spectral Responses in Quantum Efficiency of Emerging Kesterite Thin-Film Solar Cells

Abstract

The spectral responses in quantum efficiency provide essential information about current generation, recombination, and diffusion mechanisms in a photodetector, photodiode, and photovoltaic devices as the quantum efficiency is a function of the voltage and light biases and the spectral content of the bias light and/or location of the devices. Recently, P-type Kesterite thin-film solar cells are emerging as they have a high absorption coefficient (>10 4 cm À1 ) and ideal direct bandgap (1.4-1.5 eV), which make them a perfect candidate for photovoltaic application. However, a champion device from Zincblende (CdTe) or Chalcopyrite (CIGS) solar cells shows~21% efficiency (<21.5%, First Solar and <21.7%, ZSW, respectively) while Kesterite devices suffer from severe losses with <12.6% efficiency. Furthermore, the maximum theoretical efficiency based on Shockley-Queisser limit is about 32.2%, which indicates there is much room for the improvement. Consequently, the implication from the current situation highlights the need for a systematic analysis of the loss mechanism in Kesterite devices. In this work, we carried out a systematic study of the efficiency limiting factors based on quantum efficiency to model the quantum efficiency response of current CZTSSe thin-film solar cells. This will provide the guidance for proper interpretation of device behaviors when it is measured by quantum efficiency.

Investigation on limiting factors affecting Cu2ZnGeSe4 efficiency: Effect of annealing conditions and surface treatment

“…To get a deeper insight into the origin of these losses, taking into account that QE analysis affords an understanding of the photogenerated carrier collection in the device in addition to a spatial distribution of the dominant recombination path along the solar cell. Analytical descriptions have been designed to model bias-dependent quantum efficiency to study the behavior of CZTSe and CZTSe:Ge absorbers with different voltage and light bias conditions [55,56]. The QE response differs depending on the applied voltage bias (V bias ), where reverse bias seems not affecting the spectral response (optimized depletion width with improved carrier collection are conserved), whereas the forward bias (V bias = 0.2 V) induces a strong decay in QE response at long-wavelengths more specifically.…”