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Broadening the processing window is of high importance for developing efficient Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, a high efficiency (active‐area: 13.5%) of CZTSSe solar cells achieved from thioglycolic acid (TGA)‐ammonia based water solution method is first reported. The cell performance exhibits the high tolerance to the element composition variations of the CZTSSe film. Film crystallization and chemical mechanism studies reveal that this high composition‐tolerance mainly benefits from an existence of a conductive carbon framework layer with high element accommodating ability and a phase‐segregation growth behavior of CZTSSe grains driven by thermodynamics properties of the heterogeneous film system. It is shown that Sn–TGA coordination capable to induce large metal–organic molecule clusters plays a critical role in forming the mesoscopic carbon layer. These results and related material mechanism provide new routes to regulate crystal growth of the CZTSSe film for further improving cell performance.

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Aqueous precursors provide an alluring approach for low-cost and environmentally friendly production of earth-abundant Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. The key is to find an appropriate molecular agent to prepare a stable solution and optimize the coordination structure to facilitate the subsequent crystallization process. Herein, we introduce thioglycolic acid, which possesses strong coordination (-SH) and hydrophilic (-COOH) groups, as the agent and use deprotonation to regulate the coordination competition within the aqueous solution. Ultimately, metal cations are adequately coordinated with thiolate anions, and carboxylate anions are released to become hydrated to form an ultrastable aqueous solution.These factors have contributed to achieving CZTSSe solar cells with efficiency of as high as 12.2% (a certified efficiency of 12.0%) and providing an extremely wide time window for precursor storage and usage. This work represents significant progress in the non-toxic solution fabrication of CZTSSe solar cells and holds great potential for the development of CZTSSe and other metal sulfide solar cells.Photovoltaics have made great contributions to the release of global energy and environmental issues. 1 Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is one of the most environmentally friendly and inexpensive semiconductor light-absorbing materials for photovoltaic applications because of its non-toxic and earth-abundant components. [2][3][4] CZTSSe exhibits high light absorption of >10 4 cm -1 , an adjustable bandgap matching the solar spectrum, 5-9 high thermodynamic and environmental stability 10-12 and a device manufacturing process compatible with current thin film solar cells. [13][14][15][16][17][18] Solution processing of the CZTSSe thin film deposition by intermixing of precursor components at the molecular level has advantages of composition uniformity and morphology control over the conventional vacuum technique. [19][20][21][22] The hydrazine solution approach, with the advantages of high reduction and coordination ability, 23, 24 has resulted in the most efficient CZTSSe solar cells. 25 These positive results have encouraged scientists to explore the green solvent technique for CZTSSe fabrication, an ultimate trend toward non-vacuum semiconductor device production, [26][27][28] which has led to the development of a variety of solvent systems. [29][30][31][32] Certainly, among these systems, the aqueous system is the most alluring candidate from the perspective of safety, environmental effects and cost.As early attempts at aqueous precursor systems, metal salt precursor routes such as chemical bath deposition (CBD), 33 successive ionic layer adsorption and reaction (SILAR) 34, 35 and electrochemical deposition have been explored. 36,37 Spin coating using a metal salt-thiourea solution has yielded moderate efficiencies. 38,39 Strategies for synthesizing nanocrystals from aqueous solutions or preparing colloid dispersions have also been developed. Cell performance has been obviously improved through pre-synthesis ...

Large second-harmonic generation (SHG) response and broad band gap are two important and competitive parameters. It is difficult to balance them out in one material. In this work, by coupling alkali earth metal (AEM) octahedra with large highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) gap and nonlinear optical (NLO)-active tetrahedra units, nine noncentrosymmetric (NCS) compounds, belonging to a new quaternary chalcogenide family A I B 3 II C 3 III Q 8 VI with unique windmill-like [Mg 3 M 3 III Q 24 ] (M III = Al, Ga; Q = S, Se) units constructed by alternated [MgQ 6 ] octahedra and [M III Q 4 ] tetrahedra, are rationally designed and fabricated. The compounds show a stable structural framework but adjustable optical properties. Among them, NaMg 3 Ga 3 Se 8 shows a large SHG response (∼1 × AgGaS 2 (AGS)), wide band gap (in selenide) (2.77 eV), high laser-induced damage threshold (LIDT) (∼2.3 × AGS), and suitable birefringence (0.079@546 nm). It should be a potential candidate for infrared (IR) nonlinear optical (NLO) materials. The results enrich the chemical diversity of chalcogenides and open an avenue for the development of new IR NLO materials through the octahedra and tetrahedra coupled strategy.

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