How the Ge Incorporation Approach Affects Non-Radiative Recombination Losses in Cztsse Thin Film Solar Cells

Abstract

Kesterite-based thin-film solar cells (TFSCs) have regaining attention in the photovoltaic community in recent times. However, their performance still lags behind CdTe and Cu(In,Ga)Se2-based TFSCs, because of dominant non-radiative recombination losses. The unstable nature of Sn ionic states is the main cause for poor performance. The present study employs the strategy of Ge doping at different position in stacked metallic precursor layers and investigates real-time external radiative efficiency (ERE) mapping to solve this issue. The position of the Ge within the stacked metallic precursor shows distinct alloying behavior, and the density of Sn-related defects and associated defect clusters arise from two crystal evolution reaction pathways. Consequently, it offers improved grain growth and reduced density of Sn-related deep-level defects in kesterite. Furthermore, spatial ERE mapping reveals that the stacking order of the Ge significantly influences the doping uniformity for ERE. The Ge incorporation in metallic precursor results in an increased open-circuit voltage owing to significantly reduced non-radiative recombination. This study provides valuable insights into the assessment of non-radiative losses using a powerful tool, such as the ERE, which assists in the development of these devices and contributes to achieving higher power conversion efficiency (PCE) in TFSCs.

Keywords: kesterite, Ge doping, external radiative efficiency, non-radiative recombination, Voc-deficit