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• The post-heating treatment (PHT) precursor films were adopted to modify the morphology significantly. • The research results indicate that proper PH treatment can modify the surface morphology of precursor films, which is crucial for preparing high-quality absorber layers, the optimum PH temperature was 60 °C. • The best efficiency of the fabricated CZTSSe solar cell is 11.07%, with V oc of 504.6 mV, J sc of 37.69 mA/cm2, and FF of 58.19% In the solution method, the surface morphology characteristic of the precursor film is essential for obtaining the high quality of the absorber layer. Herein, the post-heating treatment (PHT) precursor films were adopted to modify the morphology significantly and the effects of different PHT temperatures on the properties of precursor films, absorber layer films, and photovoltaic devices were investigated. The precursor film with a more porous surface could be obtained by PHT, which facilitates the downward diffusion of Se easily during sulfoselenization and the formation of a large-grain-spanning monolayer structure. Furthermore, the Cu 2 ZnSn(S, Se) 4 absorber layer surface holes were significantly reduced, owing to sufficient grain growth during sulfoselenization. As a result, the device efficiency with PHT was increased to 11.07% mainly due to improved Cu 2 ZnSn(S, Se) 4 absorber spectral response. This study might provide a new potential method for adjusting precursor film morphology and thus enhancing the corresponding device performance. [ABSTRACT FROM AUTHOR]

• DMSO and MOE were proposed for the first time to improve the surface morphology of the films. • The optimum mixing ratio is V MOE = V DMSO = 2 mL, and the solution to the precursor film is completed in the air environment. • The efficiency of the fabricated CZTSSe solar cell is 10.99% with V oc of 510.6 mV, J sc of 33.19 mA/cm2, and FF of 64.83 %. A mixed dimethyl sulfoxide (DMSO) and 2-methoxy ethanol (MOE) solvent system was developed to prepare high-quality kesterite Cu 2 ZnSn(S, Se) 4 (CZTSSe) film. The precursor films made pure DMSO system show a tube-like microstructure morphology, which can be changed by adding MOE to the solution. The increase of MOE in the precursor solution is a key in the crystalline characteristic of the absorber and connecting performance with thin film solar cells. As V MOE = V DMSO , the CZTSSe layer can achieve good contact with the back electrode and obtain large grains across layers. The addition of MOE solvent effectively improves the fill factor (FF). Specifically, both the fill factor and efficiency are increased from 49.67% and 6.43% to 64.83% and 10.99%, respectively, with the addition of 2 mL of MOE into precursor solution prepared by DMSO. [ABSTRACT FROM AUTHOR]

Light trapping structure (LTS) is generally utilized to improve the short circuit current density (J s c ). However, the power conversional efficiency (P C E) of solar cells is determined by product of J s c , open circuit voltage (V o c ) and fill factor (F F). In this paper, we have quantitively investigated the role of rear LTS on the performances of perovskite solar cells based on different LTSs. The results show that rear LTS has significant impact on the reverse saturation current (J 0) , V o c and F F. Solar cells with substrate exhibit higher J 0 , is approximate 4 and 5 times higher than that of solar cells with meatal reflector and air, respectively. The ideal V o c of solar cells with metallic reflector is around 1.33 V, is approximate 20 mV and 60 mV higher than that of solar cells with air and substrate, respectively. F F is affected by not only light trapping structure but also recombination mechanisms. [ABSTRACT FROM AUTHOR]

Cu 2 Sn 1-x Ge x S 3 (CTGS) thin films were created through sulfurizing SnGe/Cu precursors deposited by the sputtering method. The effects of different sulfurization conditions on the crystallinity, morphology, composition, optical-electrical properties and chemical information of the CTGS thin films have been investigated in detail. The results demonstrate that the CTGS thin films obtained by using sulfurization temperature at 550 °C for 20min have the best crystal quality and smooth surface morphology with largest grains and the best optical-electrical properties. Meanwhile, CTGS thin films solar cell with the best performance is found that the CTGS film possesses a graded band gap structure, in which the band gap gradually become larger towards the Mo electrode, and the CdS/CTGS hetero-junction interface shows the "type I″ energy band alignment with a "spike-like" structure. As a result, the obtained bandgap-graded CTGS thin film solar cells with the best power conversion efficiency (PCE) of 3.35 (±0.04) % manifest an open-circuit voltage of 389 (±7.78) mV and a short-circuit current density of 26.98 (±0.54) mA cm−2. This work demonstrates a promising route to develop high-efficiency Cu(In,Ga)Se 2 or Cu 2 SnS 3 -based thin film solar cells. • It is the innovative to prepare Cu 2 Sn 1-x Ge x S 3 (CTGS) films and devices by sputtering alloy target. • The effects of different annealing temperature and time on properties of CTGS thin films were investigated in detail. • CTGS thin films solar cell with the best performance was found that the CTGS film exhibits a graded band gap structure. • The best PCE of 3.35 % bandgap grading CTGS device is obtained with a high open-circuit voltage of 389 mV. [ABSTRACT FROM AUTHOR]

In recent years, there is significant interest in Cu 2 SnS 3 (CTS) thin film solar cells owing to the eco-friendly nature and abundant elemental composition. However, the efficiency prepared in laboratory settings for these solar cell remains relatively low, primarily due to serious open-circuit voltage losses. Cation substitution is one of the strategies to alleviate this problem. In this work, Ag and Ge dual-cation substitution in CTS is proposed, which occupy partial Cu and Sn lattice sites respectively. Investigation reveals that substituting Cu with part Ag increases the band gap slightly, promotes grain growth, and improves crystallinity of CTS films. Simultaneously, Ge incorporation shifts the conduction band upwards to some extent, while reducing grain boundaries, due to increasing the grain size. As a result, the incorporation of 6 % Ag resulted in an optimal efficiency (PCE) of 2.78 %. Furthermore, employing dual-cation substitution with 6 % Ag and 6 % Ge is employed, the CTS device achieved an optimal efficiency of 3.15 %. This work develops the synergistic effect of Ag and Ge dual-cation substitution in CTS device and confirms that this approach can improve device performance, thus providing new research ideas for advancing the development of CTS device. • Preparation of ternary compound Cu 2 SnS 3 thin film solar cells by solution method. • Improve the crystal quality by adding different concentrations of Ag into the Cu 2 SnS 3 absorption layer. • Incorporated different amounts of Ge to Cu 2 SnS 3 absorber layer with containing 6 % Ag to obtain solar cells with higher efficiency. [ABSTRACT FROM AUTHOR]