Unveiling microscopic carrier loss mechanisms in 12% efficient Cu2ZnSnSe4 solar cells

Abstract

Understanding carrier loss mechanisms at microscopic regions is imperative for the development of high-performance polycrystalline inorganic thin-film solar cells. Despite the progress achieved for kesterite, a promising environmentally benign and earth-abundant thin-film photovoltaic material, the microscopic carrier loss mechanisms and their impact on device performance remain largely unknown. Herein, we unveil these mechanisms in state-of-the-art Cu2ZnSnSe4 (CZTSe) solar cells using a framework that integrates multiple microscopic and macroscopic characterizations with three-dimensional device simulations. The results indicate the CZTSe films have a relatively long intragrain electron lifetime of 10–30 ns and small recombination losses through bandgap and/or electrostatic potential fluctuations. We identify that the effective minority carrier lifetime of CZTSe is dominated by a large grain boundary recombination velocity (~104 cm s−1), which is the major limiting factor of present device performance. These findings and the framework can greatly advance the research of kesterite and other emerging photovoltaic materials.

10.3% Efficient Green Cd‐Free Cu2ZnSnS4 Solar Cells Enabled by Liquid‐Phase Promoted Grain Growth

“…This can be attributed to larger grain size and reduced grain boundaries, as the high recombination velocity at the grain boundaries in kesterite has been shown to dominate the effective minority carrier time. [ 12 ]…”

“…This can be attributed to larger grain size and reduced grain boundaries, as the high recombination velocity at the grain boundaries in kesterite has been shown to dominate the effective minority carrier time. [12] We further investigated the impact of the remaining L-CTS layer on the carrier transport at the rear interface. The hole transport barriers Φ b with and without L-CTS layer were estimated from temperature-dependent series resistance (R s ).…”

“…[9][10][11] The low carrier collection efficiency is usually attributed to the short minority carrier diffusion length constrained by the low minority carrier lifetime. Nevertheless, our recent electron beam induced current (EBIC) and cathodoluminescence (CL) measurements have shown that: [12] i) the grain boundary recombination velocity of kesterite is relatively high; ii) the effective minority carrier lifetime is highly likely limited by the large grain boundary recombination velocity; and iii) the recombination at near-horizontal grain boundaries in the middle of kesterite thin films is the dominating carrier loss mechanism in the quasi-neutral region, leading to significant losses in short-circuit current density (J SC ). [12,13] Furthermore, the carrier recombination at nearhorizontal grain boundaries may also deteriorate the solar cell fill factor (FF).…”

“…Nevertheless, our recent electron beam induced current (EBIC) and cathodoluminescence (CL) measurements have shown that: [12] i) the grain boundary recombination velocity of kesterite is relatively high; ii) the effective minority carrier lifetime is highly likely limited by the large grain boundary recombination velocity; and iii) the recombination at near-horizontal grain boundaries in the middle of kesterite thin films is the dominating carrier loss mechanism in the quasi-neutral region, leading to significant losses in short-circuit current density (J SC ). [12,13] Furthermore, the carrier recombination at nearhorizontal grain boundaries may also deteriorate the solar cell fill factor (FF). [14] Therefore, increasing grain size and reducing the number of grain boundaries (especially the near-horizontal ones) in the CZTS absorber is imperative.Small grain size and near-horizontal grain boundaries are known to be detrimental to the carrier collection efficiency and device performance of puresulfide Cu 2 ZnSnS 4 (CZTS) solar cells.…”

Theoretical Modeling of Perovskite–Kesterite Tandem Solar Cells for Optimal Photovoltaic Performance

“…[17,18] In spite of these drawbacks, a number of modeling studies have been done on CZTSe solar cells and a high PCE of 12.6% was reported through an experimental study. [19] A modeling study performed on CZTSe solar cell recently furnished a high optimized PCE of 18.63%. [20] Hence, the material CZTSe is selected as the absorber material for the bottom subcell of the tandem device architecture.…”