The present review gives an overview of the various reports on properties of line and planar defects in Cu(In,Ga)(S,Se)2 thin films for high‐efficiency solar cells. We report results from various analysis techniques applied to characterize these defects at different length scales, which allow for drawing a consistent picture on structural and electronic defect properties. A key finding is atomic reconstruction detected at line and planar defects, which may be one mechanism to reduce excess charge densities and to relax deep‐defect states from midgap to shallow energy levels. On the other hand, nonradiative Shockley–Read–Hall recombination is still enhanced with respect to defect‐free grain interiors, which is correlated with substantial reduction of luminescence intensities. Comparison of the microscopic electrical properties of planar defects in Cu(In,Ga)(S,Se)2 thin films with two‐dimensional device simulations suggest that these defects are one origin of the reduced open‐circuit voltage of the photovoltaic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Cu2ZnSn(S, Se)4‐based solar cells with total area (0.5 cm2) power conversion efficiency of 6.4% are demonstrated from thin film absorbers processed by inkjet printing technology of Cu‐Zn‐Sn‐S precursor ink followed by selenization. The device performance is limited by the low fill factor, which is due to the high series resistance.

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The most reported stable crystal structure of Cu 2 ZnSnS 4 and Cu 2 ZnSnSe 4 (CZTSe) is kesterite, which is derived from the ternary chalcopyrite structure. However, by controlling the reaction conditions, we found that the structure and composition of the CZTSe nanocrystals (NCs) can be tuned. This can be achieved by using a simple hot injection approach. The structural properties of the CZTSe NCs were characterized by powder X-ray diffraction (PXRD), Raman spectroscopy and transmission electron microscopy. The energy dispersive X-ray spectroscopy confirms the stoichiometry of CZTSe NCs. The optical band gap of the NCs is found to be around 1.38 eV, as estimated from UV-Vis absorption spectroscopy. PXRD studies show that the obtained CZTSe NCs occurring in three structurally different phases (tetragonal kesterite type, hexagonal wurtzite type and orthorhombic wurtz-stannite type) are converted to the kesterite structure by annealing at 540 uC for 30 min under an Se-vapour atmosphere.

Cu2ZnSnS4 (CZTS) has been considered as an alternative absorber layer to Cu(In,Ga)Se2 due to its earth abundant and environmentally friendly constituents, optimal direct band gap of 1.4-1.6 eV and high absorption coefficient in the visible range. In this work, we propose a solution-based chemical route for preparation of CZTS thin film absorbers by spin coating of the precursor inks composed of Cu3SnS4 and ZnS NPs and annealing in Ar/H2S atmosphere. X-ray diffraction and Raman spectroscopy were used to characterize the structural properties. The chemical composition was determined by energy dispersive X-ray spectroscopy. Optical properties of the CZTS thin film absorbers were studied by transmission, reflection and photoluminescence spectroscopy.