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Antimony selenide, Sb2Se3, has emerged as a promising material for p-type absorbers in thin-film photovoltaics, boasting an optimal band-gap (~1.2 eV) and a high absorption coefficient (>105 cm-1), which contribute to record cell efficiencies exceeding 10%. The photovoltaic parameters are significantly influenced by its highly anisotropic crystal structure and the absorber's very low free carrier density. This study explores various strategies to enhance the photovoltaic properties of Sb2Se3-based solar cells. Two distinct growth techniques, Radio Frequency Magnetron Sputtering (MS) and Pulsed Electron Deposition (PED), were employed to deposit Sb2Se3. The dominant crystallographic orientations were analyzed in relation to the growth techniques, deposition parameters, and different substrates used. Solar cells incorporating these absorber layers demonstrated a strong dependence of short circuit current density on the (Sb4Se6)n ribbon orientation. Additionally, Cu was evaluated as a p-type dopant for Sb2Se3 thin-films, resulting in an improvement by approximately two orders of magnitude in Cu-doped Sb2Se3 films. Corresponding solar cells showed conversion efficiency exceeding 5% and open circuit voltage > 510 mV. Furthermore, several cell architectures featuring different electron transport layers (CdS, TiO2, ZTO) and hole transport layers (Mo, FTO, MoO3, WO3) were modelled, underscoring the importance of band alignment in enhancing the Fill Factor and overall solar cell efficiency.

Cu2MnSnS4 (CMTS) is a promising candidate for application in thin film for photovoltaics (PV), thanks to sustainability and low cost of its components. Nevertheless, reported efficiencies are still poor, with a current world-record of 1.13% for a solar cell with CMTS absorber layer made by sputtering and sulfurization [1]. This work reports about a simple and low-cost synthesis procedure, starting from a solution containing all the precursors, without the need of hazardous external sulfurizing agents. CMTS thin films were made by blade coating of the solution on molybdenum substrate and followed by an annealing at 550°C under argon atmosphere, without the aid of external sulphurating agents. After annealing, samples were quenched at RT, but some selected samples underwent a slow cooling inside the furnace. Some selected CMTS thin films were subjected to HCl etching (3% HCl, at 75°C for 10 minutes). Prototype devices were made with the architecture Mo/CMTS/CdS/i-ZnO/AZO/Al grid: CdS was deposited by chemical bath deposition, i-ZnO and AZO by sputtering and Al grid was thermally evaporated. Some selected devices were subjected to a thermal treatment at 260°C for 10 minutes on titanium hotplate. After measurements of photovoltaic performances, upper layers were removed and CMTS thin films were extensively studied employing the GI-XRD technique to determine the lattice constants as well as microstructural properties like microstrain and size of coherent scattering domains. These results of the evaluation of GI-XRD data and photovoltaic performances were correlated to precursor composition, cooling conditions after annealing and post deposition treatments (i.e. HCl etching of the absorber before CdS deposition and thermal treatment of the complete device). All CMTS thin films analyzed by GI-XRD exhibited stannite structure, as expected [2], with a very good crystalline quality. The impact of metal ratio in the solution of precursors was studied, keeping copper poor condi

Cu2MnSnS4 (CMTS) is regarded as a promising material for thin film solar cells thanks to the abundance, low cost and low toxicity of its constituents and its good optical properties. The record efficiency (1.13%) is still low due to the presence of manganese oxides in the absorber [1]. In this work, CMTS was synthesized by a cheap sol-gel methodology. The thin film was made by blade coating of a solution containing metal precursors and thiourea, acting as the unique source of sulfur, followed by annealing at 550°C. The commonly used CdS was added by chemical bath deposition to act as buffer layer. Solution composition was fine-tuned and effect of deposition under controlled atmosphere and of post-deposition treatments (HCl etching of the absorber and thermal treatment of complete device at 260°) were studied. XRD and Raman spectroscopy revealed the formation of CMTS with stannite structure while optical bandgap was found to be comprised between 1.5 and 1.6 eV. X-ray photoelectron spectroscopy (XPS) was used to determine manganese oxidation state finding only Mn (II), which is the correct state in stannite structure. No oxygen was detected in the material bulk, but deposition under a controlled atmosphere was found to be important to avoid the formation of oxidized species on the samples’ surface. Besides, post-deposition treatments were found to be beneficial for photovoltaic performance, as well as device ageing. The champion device displayed 0.92% efficiency, which is the current record for wet-synthesized CMTS in substrate configuration. The still poor efficiency could be linked to CdS used as a buffer layer. XPS and energy dispersive X-rays (EDX) revealed a manganese loss from the samples’ surface due to ammonia presence in CdS chemical bath deposition; moreover, ultraviolet photoelectron spectroscopy (UPS) found a detrimental cliff-like band alignment between CMTS and CdS. [1] V. Trifiletti et al., Solar Energy Materials & Solar Cells 254 (2023) 112247

Thin film low-cost and eco-friendly photovoltaic devices are based on Cu2ZnSn(S,Se)4. To reduce production costs and improve sustainability, manganese can substitute zinc since Mn is safe and Earth-abundant, and it can be used as a light absorber1) Here, we report on the growth and characterization of Cu2MnSnS4 thin films, produced both by a two-step deposition process and by a sol-gel-based method. The metallic precursors have been deposited by sputtering, and the stack annealed at high temperatures in sulphur atmosphere. The layers, obtained in a Cu-poor and Mn-poor compositional regime, have been tested in solar devices with a record efficiency of 1.13%, with an open-circuit voltage of about 445 mV, delivered after over one year from the first PV measurement. X-ray diffraction and photoelectron, Raman, photoluminescence, and admittance spectroscopies have been used to characterize Cu2MnSnS4, and a scenario of high defectivity has emerged.2) Therefore, we moved to a sol-gel-based method, to improve the quality of the material reducing defectivity. An ink, prepared by dissolving in dimethylsulfoxide metal salts and thiourea, used as the only source of sulphur, was deposited by blade coating to obtain thin films. Sol-gel transition took place in air and then samples were annealed at 550°C under argon atmosphere. The so obtained thin films were fully characterized showing promising preliminary results. References: 1)Le Donne A., Trifiletti V., Binetti S., Front. Chem, 2019, 7:297. 2)Trifiletti V., Frioni L., Tseberlidis G., Vitiello E., Danilson M., Grossberg M., Acciarri M., Binetti S., Marchionna S., Solar Energy Materials & Solar Cells, 2023, 254 112247

Thin film low-cost and eco-friendly photovoltaic devices are based on Cu2ZnSn(S,Se)4. To reduce production costs and improve sustainability, manganese can substitute zinc since Mn is safe and Earth-abundant, and it can be used as a light absorber1) Here, we report on the growth and characterization of Cu2MnSnS4 thin films, produced both by a two-step deposition process and by a sol-gel-based method. The metallic precursors have been deposited by sputtering, and the stack annealed at high temperatures in sulphur atmosphere. The layers, obtained in a Cu-poor and Mn-poor compositional regime, have been tested in solar devices with a record efficiency of 1.13%, with an open-circuit voltage of about 445 mV, delivered after over one year from the first PV measurement. X-ray diffraction and photoelectron, Raman, photoluminescence, and admittance spectroscopies have been used to characterize Cu2MnSnS4, and a scenario of high defectivity has emerged.2) Therefore, we moved to a sol-gel-based method, to improve the quality of the material reducing defectivity. An ink, prepared by dissolving in dimethyl-sulfoxide metal salts and thiourea, used as the only source of sulphur, was deposited by blade coating to obtain thin films. Sol-gel transition took place in air and then samples were annealed at 550°C under argon atmosphere. The so obtained thin films were fully characterized showing promising preliminary results. 1)Le Donne A. et al., Front. Chem, 2019, 7:297. 2)Trifiletti V. et al., Solar Energy Materials & Solar Cells, 2023, 254 112247.

Kesterite compound Cu2ZnSnS4 is the most promising next leader in the chalcogenide thin films technology as it is based on earth-abundant elements. In this work, kesterite thin films were prepared with a wet chemistry method by using a DMSO solution containing thiourea and acetylacetone, without further addition of vapour sulfur compounds to obtain the Cu2ZnSnS4 phase. The composition and stability of the molecular precursor-ink were investigated by EPR, IR and Raman spectroscopy. Acetate precursors were proved to have a primary role in creating a network in the sol-gel transition by bridging the metals in solution, together with thiourea and DMSO coordination. The high-quality of the thin films, obtained by spin coating deposition and thermal treatment at 500°C, was assessed by XRD, Raman, Energy-Dispersive spectroscopy and optical analysis, which revealed a direct band gap of 1.5 eV. Therefore, the precursor-ink and the deposition process developed in this work are very well suitable for solar cell application.

Conventional methods for fabricating chalcogenide-based solar cells involve vacuum processes, e.g. co-evaporation and sputtering, even if the most performing devices based on the kesterite compound Cu2ZnSn(S,Se)4 have been realized using a solution-based methodology. Moreover, non-vacuum processes present significant advantages as lower production costs, higher productivity and uniformity of the final stoichiometry composition. In this context, we present a new chemical procedure to obtain a superior quality Cu2ZnSnS4 and Cu2FeSnS4 films composed by highly soluble and inexpensive precursors in a non-toxic and environmentally friendly solvent. Therefore, the films were prepared by a Sol-Gel method, starting from the metal salts in organic solvent (dimethylsulfoxide); thiourea was used as a source of sulphur. The influence of the composition of solutions containing metal ions was studied: solutions of metal salts containing non-coordinating anions and coordinates ones were compared to evaluate the role of anions and their coordination with metal ions in the formation of a pure and homogeneous phase. To obtain information about the complex mechanism of interaction between the metals and the various components of the solution Raman measurements and electronic paramagnetic resonance (EPR) were performed. The film deposition was carried out by in situ gel formation on fluorine doped tin oxide coated glass. The subsequent heat treatment guarantees the formation of the correct crystalline phase, without sulfurization but in Argon atmosphere [and at temperature suitable also for flexible and plastic substrates]. The films obtained were characterized by Raman spectroscopy, X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX), morphologically by electronic scanning electron microscopy (SEM). Raman and EPR measurements have shown that thiourea plays a primary role in coordinating metallic ions in solution, also highlighting the reductive power on copper; the coord