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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]

Improving the performance of thermoelectric (TE) materials and fabricating TE devices with higher conversion efficiency remains a significant challenge in materials research. The low figure of merit (ZT) value of n -type bismuth telluride has seriously hindered the development of TE devices based on bismuth telluride. Element doping and nanostructured defect introduction have commonly been employed to improve TE properties. Herein, we utilized high-pressure synthesis to fabricate n -type Bi 2 Se 0.3 Te 2.7 bulk nanomaterials and enhance their TE performance by adjusting the fabrication pressure and titanium doping concentration. Through this process, titanium effectively substituted bismuth to decrease carrier concentration and improve carrier mobility. As a result, the thermal conductivity was significantly decreased. By employing a fabrication pressure of 2.5 GPa and 10 at % Ti doping, a remarkable ZT value of 0.96 was achieved at 333 K, which was 2.8 times the undoped counterparts. These findings demonstrate a successful design methodology and fabrication process to generate n -type Bi 2 Te 3 with outstanding TE performance. This study provided valuable insights into the synthesis of high-performance TE materials and contributed to advancements in TE device technology. [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]