Cu2ZnSnS4 (CZTS) and its related materials such as Cu2ZnSnSe4 (CZTSe) and Cu2ZnSn(S,Se)4 (CZTSSe) have attracted considerable attention as an absorber material for thin film solar cells due to the non‐toxicity, elemental abundance, and large production capacity of their constituents. Despite the similarities between CZTS‐based materials and Cu(In,Ga)Se2(CIGS), the record efficiency of CZTS‐based solar cells remains significantly lower than that of CIGS solar cells. Considering that the difference between the two lies in the choice of the absorber material, the cause of the lower efficiency of CZTS‐based solar cells can be isolated to the issues associated with CZTS‐based materials and their related interfaces. Herein, these issues and the work done to understand and resolve them is reviewed. Unlike existing review papers, every unique region of CZTS‐based solar cells that contributes to its lower efficiency, namely: (1) the bulk of the absorber, (2) the grain boundaries of the absorber, (3) the absorber/buffer layer interface, and (4) the absorber/back contact interface are surveyed. This review also intends to identify the major unresolved issues and the potential improvement approaches of realizing sizable improvements in the solar cells' efficiency, thus providing a guide as to where research efforts should be focused. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

The synthesis of previously unknown perovskite (CH NH ) PdCl is reported. Despite using an organic cation with the smallest possible alkyl group, a 2D organic-inorganic layered Pd-based perovskites was still formed. This demonstrates that Pd-based 2D perovskites can be obtained even if the size of the organic cation is below the size limit predicted by the Goldschmidt tolerance-factor formula. The (CH NH ) PdCl phase has a bulk resistivity of 1.4 Ω cm, a direct optical gap of 2.22 eV, and an absorption coefficient on the order of 10 cm . XRD measurements suggest that the compound is moderately stable in air, an important advantage over several existing organic-inorganic perovskites that are prone to phase degradation problems when exposed to the atmosphere. Given the recent interest in organic-inorganic perovskites, the synthesis of this new Pd-based organic-inorganic perovskite may be helpful in the preparation and understanding of other organic-inorganic perovskites.

The first direct synthesis of CZTS nanocrystals in a formamide solvent system without using long hydrocarbon chain organic ligands is reported. The kesterite CZTS nanocrystals possess a mean size of 5.2 ± 1.2 nm. No secondary phases have been detected within the known limitations of XRD and Raman measurements. Experimental evidence suggests that excess S 2is present on the surface of the nanocrystals, accounting for their dispersibility in polar solvents. The nanocrystals also exhibit a smaller weight loss of 8.7% at 500°C compared to 24.4% for those capped by oleylamine. A description for the formation of CZTS FA nanocrystals and the role of formamide during synthesis is proposed. Annealing of spincoated nanocrystal thin-films highlighted the difficulty of forming dense films from loose nanocrystal films. This work shows that this can be overcome using compaction with a combination of reasonably soft metal and silicone. A means to compact the film uniformly on a centimeter scale with reduced delamination is thus demonstrated. Annealed compacted films possess crystal grains with a favorable size on the order of microns. More significantly, a large-grain layer is formed without an unwanted residual fine-grain underlayer. The absence of a fine-grain underlayer shows that this ligand exchange-free strategy is effective at resolving a key challenge associated with the nanocrystal approach of making CZTS thinfilms while simultaneously being low-cost and having a smaller environmental footprint. The strategy presented here is equally applicable to other nanocrystal approaches requiring the synthesis of dense thin-films from nanocrystal films.

Lead halide perovskites have attracted striking attention recently, due to their appealing properties. However, toxicity and stability are two main factors restricting their application. In this work, a less toxic and highly stable Pd-based hybrid perovskite was experimentally synthesized, after exploring different experimental conditions. This new hybrid organic-inorganic perovskite (CH NH ) PdBr was found to be an orthorhombic crystal (Cmce, Z=4) with lattice parameters a=8.00, b=7.99, c=18.89 Å. The Cmce symmetry and lattice parameters were confirmed using Pawley refinement and the atoms positions were confirmed based on DFT calculation. This perovskite compound was determined to be a p-type semiconductor, with a resistivity of 102.9 kΩ cm, a carrier concentration of 3.4 ×10 cm , and a mobility of 23.4 cm (V s) . Interestingly, XRD and UV/Vis measurements indicated that the phase of this new perovskite was maintained with an optical gap of 1.91 eV after leaving in air with a high humidity of 60 % for 4 days, and unchanged for months in N atmosphere; much more stable than most existing organic-inorganic perovskites. The synthesis and various characterizations of this work further the understanding of this (CH NH ) PdBr organic-inorganic hybrid perovskite material.