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The use of transparent conducting oxide (TCO) as a substrate in Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells allows for advanced applications, such as bifacial, semi-transparent, and tandem solar cells with the capability to increase power density generation. However, the efficiency of this kind of solar cell is still below 6% based on the low-cost solution process. In this work, we develop a composition gradient strategy and demonstrate a 6.82% efficient CZTSSe solar cell on F:SnO2 (FTO) substrate under the ambient condition. The composition gradient is realized by simply depositing the precursor inks with different Zn/Sn ratios. To verify that the high performance of the solar cell is attributed to the composition gradient strategy rather than the sole change of the Zn/Sn ratio, devices based on absorbers with varied Zn/Sn ratios are fabricated. Furthermore, the structure and surface morphology of the CZTSSe films with/without composition gradients are examined. The presence of elemental gradient through the depth of the CZTSSe films before and after annealing is confirmed by secondary ion mass spectroscopy analysis. It is found that the composition gradient enhances the crystallinity of the absorber, reduces the surface roughness as well as device parasitic losses, contributing to a higher fill factor, open-circuit voltage and conversion efficiency.

The application of doctor-blading for flexible solar cells is considerably attractive due to its potential upscaling feasibility via a roll-to-roll process. Herein, we report the fabrication of efficient flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells by doctor-blading under ambient conditions. The device efficiency is improved from 2.22% to 5.01% by Na incorporation, while the further enhancement is limited by inhomogeneous grain growth. To address this issue, we develop an alternative blading strategy via coating Na-containing and Na-free molecular inks by turns. By carefully tailoring this combination, compact and homogeneous CZTSSe films with large grains are obtained. Meanwhile, an appropriate amount of Na incorporation is found to be beneficial for grain growth, carrier transport, and defect passivation. Consequently, a flexible device with an efficiency of 9.63% based on the doctor-blading method is achieved. This work paves the way for the future upscaling of flexible CZTSSe solar cells via low-cost solution methods.

In the past few decades, the fabrication of solar cells has been considered as one of the most promising ways to meet the increasing energy demands to support the development of modern society as well as to control the environmental pollution caused by the combustion of fossil fuels. A number of different types of solar cells, such as silicon solar cells (Si), Cu-based chalcogenides (Cu(In,Ga)Se2/Cu2ZnSn(S,Se)4) thin film solar cells (TFSC), dye-sensitized solar cells (DSSC), organic solar cells (OSC), and perovskite solar cells (PVSC), have been implemented in the photovoltaic technology. However, the high manufacturing costs of solar cells is one of the major obstacles for their wide-scale application. In this regard, inkjet printing has attracted tremendous interest in both academic research and industrial applications among all the various kinds of fabrication techniques and is believed to be one of the most promising methods to meet these requirements. The great advantages of inkjet printing are that the process is contactless, maskless and has a high material utilization rate, and good scalability, and compatibility of the roll-to-roll process. Additionally, the maskless nature of inkjet printing allows for freedom of design, which enables multi-functional properties of solar cells (i.e., power source and artwork) to be realized. In this review, the recent advances in inkjet printing with the deposition of different layers of various types of solar cells are summarized in detail and prospectives for the future development of printed/flexible solar cells are covered.

In this work, we deposited Sb2S3 thin film with a benign molecular precursor ink based on alcohol solvent. Sb2S3 thin films with dense morphology, good crystallinity, and smooth surface were successfully prepared by optimizing the S/Sb ratio in the precursor. As-synthesized films have [hk1] preferred orientation, which is beneficial for the charge transport. The optical band gap of Sb2S3 thin film is inversely proportional to the S/Sb ratio in the precursor. This work provides a new idea and method for the application of Sb2S3 in photovoltaic.