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Thin film solar cells on semitransparent substrates are attracting much attention due to new application scenarios including building‐integrated photovoltaics (BIPV). Environmentally‐benign element constituted and highly stable kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells are ideal candidates for such applications. However, the efficiency of kesterite solar cells on semitransparent substrates is far behind that on opaque Mo‐based substrates. Here, fabrication of CZTSSe solar cells on fluorine‐doped tin oxide (FTO) substrates from molecular solution and how step‐by‐step absorber engineering improves device performance is reported. A power conversion efficiency of 7.02% is obtained when the absorber is fabricated on bare FTO, which is improved to 9.56% after adding a MoO3 interfacial layer. Investigations show the enhancement originates from the transformation of MoO3 to MoSe2 during film selenization which initiates crystallization at the back contact and at the same time prevents oversize grains at the absorber surface. Na‐doping and Ag alloying further facilitate grain growth and mitigate band tailing, resulting in a certified effective area efficiency of 11.43% with all device parameters comparable to that on an Mo‐substrate. This is the first time highly efficient kesterite solar cells are demonstrated on transparent electrodes, which opens up new opportunities for these earth‐abundant elements composed of thin film photovoltaics.

Kesterite Solar Cells The image representing article number 2300253 by Wei Huang, Hao Xin, and co‐workers depicts the architectural photovoltaic integration inspired by the Chinese building Water Cube. The work of this article is illustrated by the device structure of a kesterite solar cell on a translucent substrate applied to the building facade and the crystal structure of its absorber layer.

Solution‐processed chalcopyrite copper indium gallium sulfoselenide (Cu(In,Ga)(S,Se)2, CIGSSe) thin‐film solar cells have achieved efficiency beyond 18% and have great potential as an alternative to vacuum‐based ones. However, most of the efficient solution‐based CIGSSe solar cells are fabricated by spin‐coating in an inert atmosphere, which limits the transfer from lab protocol to industrial large‐scale production. Herein, a scalable doctor‐blading technique is applied to fabricate CuIn(S,Se)2 (CISSe) absorbers from N,N‐dimethylformamide molecular precursor solution in ambient air. With the optimization of the precursor concentration to reduce the residue solvent and change the thermal annealing process from one‐step to two‐step to separate solvent evaporation and complex decomposition to suppress fluidity, high‐quality absorber films with densely packed large grains have been fabricated and a champion CISSe solar cell with a power conversion efficiency of 12.54% has been achieved. Importantly, unlike the spin‐coating technique which may cause composition change due to the different solubilities of the precursors, the doctor‐bladed film has a composition very close to the precursor solution, which is very important for precise control of the absorber composition for industrial production.

Thin Film Solar Cells In article number http://doi.wiley.com/10.1002/solr.202200150, Weibo Yan, Hao Xin, and co‐workers fabricated high quality CuInS2 precursor films from N,N‐dimethylformamide molecular precursor solution by doctor‐blading in ambient air. CuIn(S,Se)2 solar cells with a power conversion efficiency of 12.54% on a small area and 8.43% on 1 cm2 level have been achieved from doctor‐bladed absorbers, demonstrating great potential of the solution approach for the low‐cost industrial production of CuIn(S,Se)2 thin film solar cells.