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The SnZn defect passivation and heterojunction interface energetics‐modification are crucial for further improvement of open‐circuit voltage (Voc) and efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, a simple but effective cation substitution strategy is reported to promote the performance of CZTSSe devices by simultaneously modifying the absorber and heterojunction interface. This is achieved by introducing the organic silicon salt C8H20O4Si into CZTSSe precursor solution as a source of silicon to partially substitute Sn with Si. Systematic studies reveal that there are two mechanisms synergistically contributing to the increase of efficiency: 1) This strategy can passivate the undesired SnZn defect in CZTSSe absorber more efficiently, leading to at least one order of magnitude lower SnZn defect density and beneficial carrier transport properties; 2) After Si incorporation, the conduction band minimum of the CZTSSe is upshifted, thus enlarging the bandgap, which ultimately optimizes the energy level structure at the CdS/CZTSSe interface and reduces interfacial energy loss by decreasing the carrier transport barrier. Consequently, the CZTSSe device with 7% Si substitution delivers a satisfactory efficiency of 13.02% owing to an increase in Voc. It is hoped the Si substitution strategy reported here can provide inspiration for developing advanced CZTSSe devices with broad application prospects. [ABSTRACT FROM AUTHOR]

Abundant intrinsic defects and defect clusters in Cu2ZnSn(S,Se)4 (CZTSSe) solar cells lead to severe nonradiative recombination and limited photoelectric performance. Therefore, developing effective method to suppress the detrimental defects is the key to achieve high‐efficiency solar cell. Herein, a convenient two‐step cooling strategy in selenization process is reported to suppress the CuZn and SnZn defects and defect clusters synergistically. The results show that rapid cooling during section from selenization temperature to turning temperature can inhibit the volatilization of Sn and restrain the corresponding Sn‐related defects, while slow cooling during the subsequent temperature section can reduce the degree of Cu‐Zn disorder. Benefitting from the synergistic effect of two‐step cooling, a significantly lowered concentration of SnZn and CuZn defect and their defect clusters [2CuZn+SnZn] in absorber is observed, meanwhile, a reduced band tailing effect and promoted carrier collection efficiency of the photovoltaic device is obtained. Finally, a device with improved open‐circuit voltage (Voc) of 505.5 mV and efficiency of 12.87% is achieved. This study demonstrates the impact of cooling process on defects controlling for the first time and provides a simple and effective new strategy for intrinsic defect control, which may be universal in other inorganic thin film solar cells. [ABSTRACT FROM AUTHOR]

The photovoltaic performance of the environmentally friendly Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is lower than its predecessor Cu(In,Ga)Se2 solar cells. Severe carrier recombination at the CZTSSe/CdS interface is one major reason that results in a large open‐circuit voltage loss. Doping zinc into CdS is a feasible strategy to modifying the CdS buffer layer film, but the present methods are not satisfactory. In this study, novel zinc incorporation strategy is developed to deposit a gradient composition ternary ZnxCd1–xS buffer layer for optimizing the heterojunction interface. The application of gradient composition ZnxCd1–xS buffer layer constructs a gradient conduction band energy configuration in the CZTSSe/buffer layer interface, which highly reduces the interface recombination. The suppressed interface recombination contributes to the enhanced open circuit voltage and device performance. Consequently, the CZTSSe solar cell based on gradient composition ZnxCd1–xS buffer layers achieves champion efficiency of 12.35% with VOC of 504.81 mV, JSC of 36.90 mA cm−2, and FF of 66.28%. It is worth noting that flammable and the toxic hydrazine solvent are replaced by the safe and low‐toxic 2‐methoxyethanol, making it more promising for the future commercialization of CZTSSe solar cells. [ABSTRACT FROM AUTHOR]

Despite the tremendous progress in the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic devices, open‐circuit voltage (Voc) deficit, mainly related to the SnZn‐related defects in the absorber, still remains one of the key issues that hinders the cell performance. To overcome this hurdle, here a facile synergistic post‐deposition treatment (PDT) strategy in CZTSSe family via AgF‐PDT after LiF‐PDT in the photovoltaic absorber to suppress SnZn defects, and thus, to promote the Voc and power conversion efficiency (PCE), is reported. Furthermore, a mechanism for improving device efficiency of CZTSSe cell is also proposed. The in‐depth investigation results demonstrate that Li/Ag co‐doping reduces the band tailing characteristic, enlarges the depletion region width, and enhances the carrier transport and collection, resulting in a lower bulk and interface recombination. More importantly, Li/Ag co‐doping strategy provides an effective method for SnZn defect passivation, thereby prolonging minority carrier lifetime in the ensuing devices and leading to enhancement in device performance. Correspondingly, the resulting Li/Ag co‐doped device delivers a champion efficiency of 12.58% with an impressive Voc of 507 mV. This work explores an effective strategy to kill the SnZn‐related defects, thereby overcoming the problems associated with the Voc deficit and lower cell efficiency in Kesterite‐based photovoltaic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • An In element-buried CZITSSe/CZTSSe homojunction absorber is reconstructed. • The CZITSSe/CZTSSe homojunction generates shallow-level In Zn donors. • The In Zn donors suppress defect clusters and enlarge the surface band bending. • Achieve an active-area efficiency of 13.59 % with a high V oc of 0.527 V. The Cu 2 ZnSn(S,Se) 4 solar cells (CZTSSe) are emerging as a hot area of low-cost thin film photovoltaic technology owing to its non-toxicity and excellent photoelectric properties. However, the large open-circuit voltage deficit (V oc,deficit) caused by the inherently defective CdS/ CZTSSe heterojunction interface is still a huge challenge for improving power conversion efficiency. Herein, we reconstruct the heterojunction interface by inserting a CZTSSe:In into the CdS/CZTSSe heterojunction through an In 2 Se 3 post-deposition treatment. The local occupation of In3+ at Zn2+ and Sn4+ sites decreases the disordered Zn- and Sn-related deep defects and generates benign In Zn donors within CZITSSe transition layer simultaneously, which effectively enhances the surface p-to-n conversion. The combination of chemical and field-effect passivation regulates the charge extraction and passivates the charge recombination. As a result, the In element-buried absorber enables the V oc boost from 488 to 527 mV with an impressive active-area efficiency of 13.59 %. These results demonstrate the great potential of the In element-buried absorber in alleviating the V oc,deficit and enhancing the performance of CZTSSe solar cells. [ABSTRACT FROM AUTHOR]