Search

The rapidly expanding demand for photovoltaics (PVs) requires stable, quick, and easy to manufacture solar cells based on socioeconomically and ecologically viable earth-abundant resources. Sb2S3has been a potential candidate for solar PVs and the efficiency of planar Sb2S3thin-film solar cells has witnessed a reasonable rise from 5.77% in 2014 to 8% in 2022. Herein, the aim is to bring new insight into Sb2S3solar cell research by investigating how the bulk and surface properties of the Sb2S3absorber and the current–voltage and deep-level defect characteristics of solar cells based on these films are affected by the ultrasonic spray pyrolysis deposition temperature and the molar ratio of thiourea to SbEX in solution. The properties of the Sb2S3absorber are characterized by bulk- and surface-sensitive methods. Solar cells are characterized by temperature-dependent current–voltage, external quantum efficiency, and deep-level transient spectroscopy measurements. In this paper, the first thin-film solar cells based on a planar Sb2S3absorber grown from antimony ethyl xanthate (SbEX) by ultrasonic spray pyrolysis in air are demonstrated. Devices based on the Sb2S3absorber grown at 200 °C, especially from a solution of thiourea and SbEX in a molar ratio of 4.5, perform the best by virtue of suppressed surface oxidation of Sb2S3, favorable band alignment, Sb-vacancy concentration, a continuous film morphology, and a suitable film thickness of 75 nm, achieving up to 4.1% power conversion efficiency, which is the best efficiency to date for planar Sb2S3solar cells grown from xanthate-based precursors. Our findings highlight the importance of developing synthesis conditions to achieve the best solar cell device performance for an Sb2S3absorber layer pertaining to the chosen deposition method, experimental setup, and precursors.

The use of CdSe layers has recently emerged as a route to improving CdTe photovoltaics through the formation of a CdTe(1–x)Sex(CST) phase. However, the extent of the Se diffusion and the influence it has on the CdTe grain structure has not been widely investigated. In this study, we used transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD) to investigate the impact of growing CdTe layers on three different window layer structures CdS, CdSe, and CdS/CdSe. We demonstrate that extensive intermixing occurs between CdS, CdSe, and CdTe layers resulting in large voids forming at the front interface, which will degrade device performance. The use of CdS/CdSe bilayer structures leads to the formation of a parasitic CdS(1–x)Sexphase. Following removal of CdS from the cell structure, effective CdTe and CdSe intermixing was achieved. However, the use of sputtered CdSe had limited success in producing Se grading in CST.

The crystal structure of Sb2Se3gives rise to unique properties that cannot otherwise be achieved with conventional thin-film photovoltaic materials, such as CdTe or Cu(In,Ga)Se2. It has previously been proposed that grain boundaries can be made benign provided only the weak van der Waals forces between the (Sb4Se6)nribbons are disrupted. Here, it is shown that non-radiative recombination is suppressed even for grain boundaries cutting across the (Sb4Se6)nribbons. This is due to a remarkable self-healing process, whereby atoms at the grain boundary can relax to remove any electronic defect states within the band gap. Grain boundaries can, however, impede charge transport due to the fact that carriers have a higher mobility along the (Sb4Se6)nribbons. Because of the ribbon misorientation, certain grain boundaries can effectively block charge collection. Furthermore, it is shown that CdS is not a suitable emitter to partner Sb2Se3due to Sb and Se interdiffusion. As a result, a highly defective Sb2Se3interfacial layer is formed that potentially reduces device efficiency through interface recombination.