Herein, we report a facile process, i.e., controlling the initial chamber pressure during the postdeposition annealing, to effectively lower the band tail states in the synthesized CZTSSe thin films. Through detailed analysis of the external quantum efficiency derivative ( dEQE/ dλ) and low-temperature photoluminescence (LTPL) data, we find that the band tail states are significantly influenced by the initial annealing pressure. After carefully optimizing the deposition processes and device design, we are able to synthesize kesterite CZTSSe thin films with energy differences between inflection of d(EQE)/dλ and LTPL as small as 10 meV. These kesterite CZTSSe thin films enable the fabrication of solar cells with a champion efficiency of 11.8% with a low V deficit of 582 mV. The results suggest that controlling the annealing process is an effective approach to reduce the band tail in kesterite CZTSSe thin films.

Therefore, an ever-growing demand for sustainable and environmentally-friendly energy technologies are prompting scientists to explore alternative approaches to reduce the carbon footprint. [2] Among the different sustainable energy sources, solar energy is an inexhaustible source of energy (173000 Terawatt (TW), almost 10 000 times of 17.7 TW, global energy consumption in 2020) and the largest currently available on earth with a ubiquitous distribution worldwide. [3] However, its decentralized and intermittent nature poses a great challenge to our energy needs. [4] Artificial photosynthesis, imitating a natural photosynthesis, where the harvesting of sunlight directly into chemical bonds (hydrogen, (H 2 ) fuel) is a highly promising approach to address the serious issue like air pollution, greenhouse gas emission, etc. Artificial photosynthesis by means of photoelectrochemical (PEC) water splitting has been studied extensively to split water using sunlight and semiconductor into oxygen (O 2 ) and H 2 , where the generated H 2 can be stored and transported to other energy conversion systems. [5] In recent years, PEC water splitting turned out to be an elegant and ecological way to generate clean H 2 fuel. Despite having mature and commercialized technologies, photovoltaic-electrochemical (PV-EC) water splitting systems have the most significant complications in PV designs. [6] In a photocatalytic (PC) water splitting system, on the other hand, both H 2 and O 2 are generated on the same surface of the PC particles, and hence in most cases, backward complex reactions like hydrogen oxidation reaction and oxygen reduction reaction occur quickly, lowering the solar to H 2 (STH) conversion efficiency. [7] In comparison to the PC system, the physical separation of oxidation and reduction species in PEC cells makes them more practical, effective, and safer. Moreover, the PEC cells have an electrode/electrolyte interface that performs simultaneous roles of light-harvesting and electrolysis in a single reactor. Consequently, the large-scale application of PEC cells is the most achievable, even at lower operating temperature as it opens up the opportunity to improve efficiency and reduce costs through the nature of its device structure. In particular, a recent assessment of its practicability has shown that the lifespan (i.e., stability), efficiency, and capital cost of The photoelectrochemical (PEC) cell that collects and stores abundant sunlight to hydrogen fuel promises a clean and renewable pathway for future energy needs and challenges. Monoclinic bismuth vanadate (BiVO 4 ), having an earthabundancy, nontoxicity, suitable optical absorption, and an ideal n-type band position, has been in the limelight for decades. BiVO 4 is a potential photoanode candidate due to its favorable outstanding features like moderate bandgap, visible light activity, better chemical stability, and cost-effective synthesis methods. However, BiVO 4 suffers from rapid recombination of photogenerated charge carriers that have impeded further imp...

With the earth's abundance of kesterite, recent progress in chalcogenide based Cu2ZnSn(Sx,Se1-x)4 (CZTSSe) thin films has drawn prime attention in thin film solar cells (TFSCs) research and development. This review is focused on the current developments in the synthesis of CZTS nanocrystals (NCs) using a hot injection (HI) technique and provides comprehensive discussions on the current status of CZTSSe TFSCs. This article begins with a description of the advantages of nanoparticulate based thin films, and then introduces the basics of this technique and the corresponding growth mechanism is also discussed. A brief overview further addresses a series of investigations on the developments in the HI based CZTSSe NCs using different solvents in terms of their high toxicity to environmentally benign materials. A variety of recipes and techniques for the NCs ink formulation and thereby the preparation of absorber layers using NC inks are outlined, respectively. The deposition of precursor thin films, post-deposition processes such as sulfurization or selenization treatments and the fabrication of CZTSSe NCs based solar cells and their performances are discussed. Finally, we discussed concluding remarks and the perspectives for further developments in the existing research on CZTSSe based nanoparticulate (NP) TFSCs towards future green technology.

In the development of low-cost, efficient, and environmentally friendly thin-film solar cells (TFSCs), the search continues for a suitable inorganic colloidal nanocrystal (NC) ink that can be easily used in scalable coating/printing processes. In this work, we first report on the colloidal synthesis of pure wurtzite (WZ) Cu2SnS3 (CTS) NCs using a polyol-mediated hot injection route, which is a nontoxic synthesis method. The synthesized material exhibits a random distribution of CTS nanoflakes with an average lateral dimension of ∼94 ± 15 nm. We also demonstrate that CTS NC ink can be used to fabricate low-cost and environmentally friendly TFSCs through an ethanol-based ink process. The annealing of as-deposited CTS films was performed under different S vapor pressures in a graphite box (volume; 12.3 cm3), at 580 °C for 10 min using a rapid thermal annealing (RTA) process. A comparative study on the performances of the solar cells with CTS absorber layers annealed under different S vapor pressures was conducted. The device derived from the CTS absorber annealed at 350 Torr of S vapor pressure showed the best conversion efficiency 2.77%, which is the first notable efficiency for an CTS NCs ink-based TFSC. In addition, CTS TFSC’s performance degraded only slightly after 50 days in air atmosphere and under damp heating at 90 °C for 50 h, indicating their good stability. These results confirm that WZ CTS NCs may be very attractive and interesting light-absorbing materials for fabricating efficient solar-harvesting devices.