Impact of light soaking on absorber and buffer layer in thin film solar cells
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Impact of light soaking on absorber and buffer layer in thin film solar cells Atul Kumar1 · Pranay Ranjan2 Received: 31 January 2020 / Accepted: 29 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Light soaking in thin film solar cells shows both beneficial and detrimental impact on efficiency depending upon the absorber–buffer pair. We here numerically simulated the advantageous and detrimental impact of light soaking behavior as experimentally observed in the literature by utilizing suitable defect models for the two cases, respectively. The proposed models are based on the photoconductivity and metastable photo-induced activity of absorber and buffer layers. It is observed that light soaking in absorber layer vis-a-vis photo-induced defect in absorber is beneficial for device performance. Photogenerated defect in absorber acts as hole doping which is turn enhance the built-in voltage. The photoconductivity of the buffer layer is detrimental to the device performance. The photo-generated defects in the buffer cause lowering of fill-factor, current, accelerate interfacial recombination and depreciate overall efficiency. Keywords Light soaking · Metastability · Acceptors defects · Thin film solar cells
1 Introduction Thin film solar cells of abundant and low-cost material are potential future energy source. However, these solar cells have much of the technological optimization still to be perfected and controlled before it could overtake as stable energy source. Optimization is challenging due to variety of involved variable such as radiation, thermal, atmospheric stresses in addition to non-uniformities related to thin film hetero-structures fabrications [1]. One such issue relating the performance is the light soaking behavior of thin film solar cells of CIGS [2–9], CdTe [10], CZTS [11, 12]. This phenomena cause efficiency increase after light soaking for some combination of absorber–buffers, e.g., CIGS-ZnS [5]. The same light soaking effect shows efficiency decrease for some combination of absorber–buffer like CIGS-CdS [13], etc. Other technologies like hybrid and organic solar cell [14] also show efficiency variation with light soaking. A solar cell device upon prolonged exposure to light has small * Atul Kumar [email protected] 1
Department of ECE, KL University, Guntur, Andhra Pradesh 522502, India
Department of Physics, UAE University, Abu Dhabi 15551, United Arab Emirates
2
transient variation in efficiency. The efficiency variation upon light soaking significantly affects the long-term power output and more importantly have associated challenges of lifetime/stability of solar cell. The slight decay in efficiency accumulates to significant power losses and revenues losses to the large-scale installers with main perspective as profitability. Thus, it becomes necessary to figure out deriving causes of detrimental effect of light soaking and avoiding them. Photoconductivity and low bandgap of buffer layer are one of the possible causes for the light-dependent be
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