Engineering of Interface and Bulk Properties in Cu₂ZnSn(S,Se)₄ Thin-Film Solar Cells with Ultrathin CuAlO₂ Intermediate Layer and Ge Doping

Abstract

Recently, kesterite-based absorbers and related compounds have been considered as promising eco-friendly light absorber materials for thin-film solar cells (TFSCs). However, the device performances of kesterite-based TFSCs are limited because of the formation of defects and poor interfacial properties. In this study, we developed a strategic approach to improve the device performances of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells using back-interface passivation of the absorber layer and further reduced the formation of defects through Ge doping. The application of CuAlO 2 (CAO) as an intermediate layer near the back interface efficiently improves the grain growth and minimizes the detrimental Mo(S,Se) 2 thickness. In addition, the Ge nanolayer deposited over the CAO layer improves the absorber bulk quality, effectively suppresses the defect density, and reduces the nonradiative carrier recombination losses. As a result, the short-circuit current density, fill factor, and power conversion efficiency of the champion device with the CAO and Ge nanolayer improved from 31.91 to 36.26 mA/cm 2 , 0.55 to 0.61, and 8.58 to 11.01%, respectively. This study demonstrates a potential approach to improve the performances of CZTSSe TFSCs using a combination of back-interface passivation and doping.

In Search of Disorder Transitions and Defects Within Cu2ZnSn(S,Se)4‐Based Absorber Layers via Temperature‐Dependent Raman Spectroscopy Technique

“…The detailed kesterite CZTSSe absorber thin‐film preparation, device fabrication, and characterization techniques used in this study can be found in the Supporting Information and our previous reports. [ 21,41 ]…”

Overcoming the limitations of low-bandgap Cu2ZnSn(S,Se)4devices under indoor light conditions: from design to prototype IoT application

“…37 Precursors were deposited from individual metallic targets in stacked layers, i.e., Zn (bottom)/Sn/ Cu(top), using the direct-current (DC) magnetron sputtering method. For double-cation doping, i.e., Ag (8 nm) 27 and Ge (10 nm), 36 ultrathin layers were deposited individually at different stages (Ge at the bottom and Ag at the top of the precursor) using the thermal evaporation method. The precursors and Ag-Ge-doped samples were then so annealed at 300 °C for 60 min in an Ar atmosphere at a ramping rate of 10 °C min −1 to achieve Cu-Zn and Cu-Sn alloys with smooth morphologies.…”

“…To achieve this, we used individually optimized doping conditions such as thickness and position for the Ag and Ge cations. 20,27,36 The deposition of Ag and Ge at the top and bottom of the precursor, respectively, improved the device performance under standard test conditions more than the undoped CZTSSe device. Further, a similar device tested under different light intensity conditions of white LED (WLED) and uorescent lamps (4000 K) (FL-4000K) revealed improved V oc losses with higher PCE outputs for the CZTSSe:Ag-Ge device.…”

A Critical Review on the Progress of Kesterite Solar Cells: Current Strategies and Insights

“…Various materials, including metals, [138,139] metal oxides, [140][141][142] metal chalcogenides, [95] metal nitride, [143,144] organic, [49,145,146] and other non-organic materials, [147,148] have been proposed as effective intermediate layers between Mo and kesterite. Gour et al reported 10.54% efficiency CZTSSe solar cells by introducing a 1.2 nm CuAlO 2 (CAO) nanolayer at the back interface.…”

“…Various materials, including metals, [ 138,139 ] metal oxides, [ 140–142 ] metal chalcogenides, [ 95 ] metal nitride, [ 143,144 ] organic, [ 49,145,146 ] and other non‐organic materials, [ 147,148 ] have been proposed as effective intermediate layers between Mo and kesterite. Gour et al.…”