Kesterite Cu₂ZnSnS₄ as a Low-Cost Inorganic Hole-Transporting Material for High-Efficiency Perovskite Solar Cells

Kesterite-structured quaternary semiconductor Cu₂ZnSnS₄ (CZTS) has been commonly used as light absorber in thin film solar cells on the basis of its optimal bandgap of 1.5 eV, high absorption coefficient, and earth-abundant elemental constituents. Herein we applied CZTS nanoparticles as a novel inorganic hole transporting material (HTM) for organo-lead halide perovskite solar cells (PSCs) for the first time, achieving a power conversion efficiency (PCE) of 12.75%, which is the highest PCE for PSCs with Cu-based inorganic HTMs reported up to now, and quite comparable to that obtained for PSCs based on commonly used organic HTM such as 2,2′,7,7′-tetrakis­(<i>N,N</i>-di-<i>p</i>-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD). The size of CZTS nanoparticles and its incorporation condition as HTM were optimized, and the effects of CZTS HTM on the optical absorption, crystallinity, morphology of the perovskite film and the interface between the perovskite layer and the Au electrode were investigated and compared with the case of spiro-MeOTAD HTM, revealing the role of CZTS in efficient hole transporting from the perovskite layer to the top Au electrode as confirmed by the prohibited charge recombination at the perovskite/Au electrode interface. On the basis of the effectiveness of CZTS as a low-cost HTM competitive to spiro-MeOTAD in PSCs, we demonstrate the new role of CZTS in photovoltaics as a hole conductor beyond the traditional light absorber

V₂O₅ as Hole Transporting Material for Efficient All Inorganic Sb₂S₃ Solar Cells

This research demonstrates that V₂O₅ is able to serve as hole transporting material to substitute organic transporting materials for Sb₂S₃ solar cells, offering all inorganic solar cells. The V₂O₅ thin film is prepared by thermal decomposition of spin-coated vanadium­(V) triisopropoxide oxide solution. Mechanistic investigation shows that heat treatment of V₂O₅ layer has crucial influence on the power conversion efficiency of device. Low temperature annealing is unable to remove the organic molecules that increases the charge transfer resistance, while high temperature treatment leads to the increase of work function of V₂O₅ that blocks hole transporting from Sb₂S₃ to V₂O₅. Electrochemical and compositional characterizations show that the interfacial contact of V₂O₅/Sb₂S₃ can be essentially improved with appropriate annealing. The optimized power conversion efficiency of device based on Sb₂S₃/V₂O₅ heterojunction reaches 4.8%, which is the highest power conversion efficiency in full inorganic Sb₂S₃-based solar cells with planar heterojunction solar cells. Furthermore, the employment of V₂O₅ as hole transporting material leads to significant improvement in moisture stability compared with the device based organic hole transporting material. Our research provides a material choice for the development of full inorganic solar cells based on Sb₂S₃, Sb₂(S,Se)₃, and Sb₂Se₃

Efficient In Situ Sulfuration Process in Hydrothermally Deposited Sb₂S₃ Absorber Layers

Sulfuration plays a decisive role in enhancing crystal growth and passivate defects in the fabrication of high-efficiency metal-sulfide solar cells. However, the traditional sulfuration process always suffers from high-price professional equipment, tedious processes, low activity of S, or high toxicity of H2S. Here, we develop a desired in situ sulfuration by introducing tartaric acid additive into the hydrothermal deposition process of Sb2S3. Tartaric acid, sodium thiosulfate, and potassium antimony tartaric can form Sb2Sx-contained (x > 3) as-prepared films. Encouragingly, the annealing becomes an inspiring in situ sulfuration process, which can obtain a more compact absorber layer. In addition, the crystallinity and defect property of the Sb2S3 film are also improved significantly. Finally, we achieve a high-performance Sb2S3 solar cell with a power conversion efficiency of 6.31%, which shows an encouraging enhancement of ∼15% compared with the traditional hydrothermal process. This study provides an innovative way to prepare high-efficiency Sb2S3 solar cells and provides a desirable guide to realize the in situ sulfuration process