At present, Kesterite-based thin-film solar cells, such as Cu 2 ZnSnS 4 solar cells, involve serious band-tailed states, which leads to low open-circuit voltage, thereby hindering the further improvement of device performance. In stannite-based materials, such as Cu 2 CdSnS 4 , the substitution of Zn with Cd can effectively suppress Cu Cd -related point defects and defect clusters; thus, the band-tailing state is few, which has attracted considerable research attention. In this work, on the basis of using optimized sulfurization and optimizing ratios (Cu/Cd+Sn) and temperatures, Cu 2 CdSnS 4 thin films can be obtained with good quality and single-phase composition, in which the device prepared at a ratio of 0.83 and 590 °C has the highest efficiency. Defect analysis shows that the substitution of Zn with Cd can effectively reduce Cu Cdrelated defects and defect clusters (such as 2Cu Cd +Sn Cd ) and also decrease Urbach energy, fluctuations of bandgap, and electrostatic potential compared with kesterite-based devices. In particular, Cu 2 CdSnS 4 thin-film solar cell prepared under optimized conditions (the ratio of 0.83 and 590 °C) has the minimum reverse saturation current, red shift, and the maximum minority carrier diffusion length. Therefore, an efficiency over 10% Cu 2 CdSnS 4 thin-film solar cell is reported, which shows the highest efficiency among stannitebased solar cells to date.
The use of different Sn valence states (such as Sn4+ and Sn2+) in the Cu2ZnSn(S,Se)4 (CZTSSe) precursor solution is especially important for the quality of the subsequent growth of the CZTSSe films. The latest study has found that replacing SnCl2·2H2O with anhydrous SnCl4 can remarkably improve the performance of CZTSSe solar cells, but it needs to be operated in the glovebox. Herein, for the precursor solution, SnCl4·5H2O powder is used instead of anhydrous SnCl4 in air environment, and the proportion of Sn4+ and Sn2+ precursor solutions is further systematically studied. When the ratio of Sn4+ to Sn2+ is 1:1, a uniform, compact, and noncracking CZTSSe thin film is obtained, effectively alleviating the interface recombination and reducing the concentration of deep‐level defects. In particular, the concentration of CuZn antisite defects is decreased by an order of magnitude, and the carrier recombination and band tail effect are alleviated. When JSC is maintained, VOC and FF are considerably improved. Finally, CZTSSe thin‐film solar cells are fabricated with an efficiency of over 11%. Herein, the feasibility of controlling the ratio of Sn4+ to Sn2+ in the CZTSSe precursor solution for higher efficiency of CZTSSe thin‐film solar cells is demonstrated.
Ag-alloyed Cu2ZnSn(S,Se)4 kesterite semiconductors have recently been attracting considerable attention recently because doping with Ag can suppress the CuZn related anti-site defects, which is the main factor that limits the...
Optimization of the back contact interface is crucial for improving the performance of Cu2ZnSnS4 (CZTS) thin film solar cells. In this paper, self‐depleted CuSCN is deployed as an intermediate layer at the Mo/CZTS interface to improve the quality of the back contact. This CuSCN layer, obtained via aqueous solution processing, reduces the thickness of Mo(S,Se)2 and eliminates multi‐layer crystallization of the absorber by suppressing the undesirable reaction between Mo and Se during the selenization process. By regulating the selenium infiltration into the CZTS precursor films during the selenization process, highly crystalline, single‐layer Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers are realized. The single‐layer CZTSSe absorber exhibits reduced carrier recombination, enhanced carrier density and increased work function. The improved back contact and absorber layer enables 11.1% power‐conversion‐efficiency to be achieved.
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