Tuning the Se Content in Cu₂ZnSn(S, Se)₄ Absorber to Achieve 9.7% Solar Cell Efficiency from a Thiol/Amine-Based Solution Process

Abstract

The Se content in a Cu2ZnSn­(S, Se)4 absorber layer has a significant impact on the electronic properties, but it is rather challenging to control the Se/(S + Se) ratio due to a complicated selenization process. Here, a low-toxicity thiol/amine-based solution process was developed to tune the Se content in a Cu2ZnSn­(S, Se)4 absorber layer to an optimal value by ingeniously controlling the SeO2 in the precursor solution. We demonstrated that the crystal growth and the band gap of Cu2ZnSn­(S, Se)4 thin films are affected by the Se/(S + Se) ratio. By this approach, the open-circuit voltage deficit (V oc,def) of the device was effectively decreased, and the short-circuit density (J sc) and fill factor (FF) were remarkably improved; thus, the power conversion efficiency of the Cu2ZnSn­(S, Se)4 solar cells was successfully increased from 5.6% to 9.7% for the optimal band gap (E g = 1.13 eV).

Green Atmospheric Aqueous Solution Deposition for High Performance Cu2ZnSn(S,Se)4 Thin Film Solar Cells

“…The peak positions and splitting values observed correspond well with the report for CZTSSe and are corroborated by the expected values for Cu + , Zn 2+ , and Sn 4+ . From the XPS results, two weak shoulder peaks (≈496.5 eV) are located near the Sn 3d 3/2 peak, which can be attributed to the Zn‐Auger peak L3M45M45 and become weak in Sample A . Furthermore, the high‐resolution XPS data for the two as‐prepared CZTS films deposited in air (Sample A) and in argon (Sample B) were also recorded and are shown in Figure S1, Supporting Information.…”

“…[13,32] From the XPS results, two weak shoulder peaks (%496.5 eV) are located near the Sn 3d 3/2 peak, which can be attributed to the Zn-Auger peak L3M45M45 and become weak in Sample A. [22,33] Furthermore, the high-resolution XPS data for the two as-prepared CZTS films deposited in air (Sample A) and in argon (Sample B) were also recorded and are shown in Figure S1, Supporting Information. The XPS results further firmly demonstrate that the valence state of the constituent elements can not be changed by spin-coating/annealing in air.…”

“…The active area of the CZTSSe device was defined based on a mask area of 0.21 cm 2 (≈91% of the total device area). For more information on the fabrication process, please refer to the works we have reported …”

“…For more information on the fabrication process, please refer to the works we have reported. [13,22,24,44] Characterization: XRD patterns were obtained using a Bruker D8 Advance X-ray diffractometer. Raman spectra were collected through a Renishaw inVia Raman microscope system with an excitation laser wavelength of 532 nm.…”

“…[21] More importantly, in order to prevent the metal in the precursors from being oxidized, most solution preparation methods have to be carried out under the protection of inert gas in the process of sintering as-prepared CZTS films. [22][23][24][25] This will undoubtedly increase the costs of equipments and consumable materials. Thus, it is urgently needed to eliminate the toxic solvents, reduce production costs, and simplify operation procedure for CZTSSe thin film PV devices.…”