Search

In recent years, the primary reasons for low efficiency Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells have been attributed to Sn Zn defects and related defect clusters, as well as the balance of absorption layer bandgap for short-circuit current density (J sc) and open-circuit voltage (V oc). Ge gradient has been theoretically proven to be an effective strategy to change traditional flat bandgap structure and suppress Sn Zn defects and related defect clusters for improving the device performance of CZTSSe solar cells. However, the potential of Ge gradient has not been fully verified. In this work, Ge doping effectively reduces the formation of Sn Zn defects and [2Cu Zn + Sn Zn ] defect clusters in the CZTSSe absorption layer. In addition, it can be found that the construction of the V-type bandgap is the best solution for balancing between V oc and J sc. By using the bandgap grading strategy, the disparity between the recombination barrier of the junction and the optical bandgap's minimum value is widened, thereby obtaining a large V oc. The V-type doped device has the highest efficiency when V oc is 0.45 V, which can reach 8.03%. This Ge graded substitution method provides an alternative absorption layer structure for improving V oc and the preparation of future high-efficiency kesterite photovoltaic devices. [ABSTRACT FROM AUTHOR]

Crystallization growth occupies a crucially important role in terms of impacting the film microstructure and device characteristics of the kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cell. Previous studies frequently observed that the selenized CZTSSe film consists of a multiple-layer structure with a large-grained top layer and a fine-grained bottom layer. Herein, a novel strategy is proposed for adjusting spin-coated layers and conducting two-step selenization to promote the fine-grain layers growth of Bi-doped CZTSSe (CZTBiSSe) films for high-performance solar cells. This study systematically investigates the effects of spin-coated layers and the selenization process on growth kinetics of the CZTBiSSe films. By comparison, the optimal spin-coated layer can be identified as "7 + 3", the CZTBiSSe film has a bilayer large grain structure from up to down, which reduces the grain boundaries, thus reducing the charge recombination loss, and is more conducive to charge carrier transfer. Finally, a CZTBiSSe solar cell with the highest efficiency of 7.27 % was obtained, which increased by 36 % more than one prepared using traditional methods (5.34 %). [ABSTRACT FROM AUTHOR]

Element doping into the Cu 2 ZnSn(S,Se) 4 (CZTSSe) absorber is an effective method to optimize the performance of thin film solar cells. In this study, the Cu 2 In x Zn 1-x Sn(S,Se) 4 (CIZTSSe) precursor film was deposited by magnetron cosputtering technique using indium (In) and quaternary Cu 2 ZnSnS 4 (CZTS) as targets. Meanwhile, the In content was controlled using the direct current (DC) power on In target (P In). A single kesterite CIZTSSe alloy was formed by successfully doping a small number of In3+ into the main lattice of CZTSSe. The partial Zn2+ cations were substituted by In3+ ions, resulting in improving properties of CZTSSe films. Morphological analysis showed that large grain CIZTSSe films could be obtained by doping In. The well-distributed, smooth, and dense film was obtained when the P In was 30 W. The band gap of CIZTSSe could be continuously adjusted from 1.27 to 1.05 eV as P In increased from 0 to 40 W. In addition, the CIZTSSe alloy thin film at P In = 30 W exhibited the best p-type conductivity with Hall mobility of 6.87 cm2V−1s−1, which is a potential material as the absorption layer of high-performance solar cells. [ABSTRACT FROM AUTHOR]

(Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 thin films with a single kesterite phase were synthesized using a sol-gel spin-coating method accompanied by rapid post-annealing. In this study, we investigated the effect of selenization time on the crystal quality and photoelectric performance of the (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 films. It was found that the crystallinity and morphology of the films was enhanced, and some of bigger Se substituted for the S site in (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 with increasing the selenization time. The bandgap of the film can be regulated from 1.04 eV to 0.99 eV by varying the selenization time. In addition, all films showed p-type conductive characteristics, and films with optimal electrical performance could be obtained by optimizing the selenization time. Finally, the (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 thin film with the best crystal quality and optical-electrical characteristics was obtained at an optimized selenization time of 15 min. A high power conversion efficiency (PCE) of 3.92% was obtained for the (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 device, which is 42% higher compared to that of the undoped Cu 2 ZnSn(S,Se) 4 (CZTSSe) device. [ABSTRACT FROM AUTHOR]