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Polycrystalline Cu(InGa)Se2(CIGS) thin film is a well-known light absorber material for photovoltaic solar cells. However, the mechanism of the benignity of its grain boundary (GB) remains in dispute. By using a combination of experimental techniques, we have systematically investigated the compositions, structures, and properties of the grain interior (GI) and GB of the polycrystalline CIGS films at nanometer scale. A definitive Cu deficient layer with thickness depending on the overall Cu content of the films was observed near the non Σ3 GBs with distinctly different characteristics from GIs. The band alignment between GB and GI was discovered to be of type II with downward offset for both conduction and valence bands at GB, well correlating to the local copper deficiency and structure. Our findings expressively support the type inversion and large hole barrier in this GB layer, and establish a comprehensive mechanism for the benignity of the CIGS grain boundaries towards carrier recombination.

Owing to its superior visible light absorption and high chemical stability, chalcogenide perovskite barium zirconium sulfide (BaZrS3) has attracted significant attention in the past few years as a potential alternative to hybrid halide perovskites for optoelectronics. However, the high processing temperatures of BaZrS3thin films at above 1000 ℃ severely limits their potential for device applications. Herein, we report the synthesis of BaZrS3thin films at temperatures as low as 500 ℃, by changing the chemical reaction pathway. The single phase BaZrS3thin film was confirmed by X-ray diffraction and Raman spectroscopy. Atomic force microscopy and scanning electron microscopy show that crystalline size and surface roughness were consistently reduced with decreasing annealing temperature. The lower temperatures further eliminate sulfur vacancies and carbon contaminations associated with high temperature processing. The ability to synthesize chalcogenide perovskite thin films at lower temperatures removes a major hurdle for their device fabrication. The photodetectors demonstrate fast response and an on/off ratio of 80. The fabricated field effect transistors show an ambipolar behavior with electron and hole mobilities of 16.8 cm2/Vs and 2.6 cm2/Vs, respectively.

BaZrS3is a prototypical chalcogenide perovskite, an emerging class of unconventional semiconductor. Recent results on powder samples reveal that it is a material with a direct band gap of 1.7–1.8 eV, a very strong light-matter interaction, and a high chemical stability. Due to the lack of quality thin films, however, many fundamental properties of chalcogenide perovskites remain unknown, hindering their applications in optoelectronics. Here we report the fabrication of BaZrS3thin films, by sulfurization of oxide films deposited by pulsed laser deposition. We show that these films are n-type with carrier densities in the range of 1019-1020 cm−3. Depending on the processing temperature, the Hall mobility ranges from 2.1 to 13.7 cm2/Vs. The absorption coefficient is > 105 cm−1 at photon energy >1.97 eV. Temperature dependent conductivity measurements suggest shallow donor levels. By assuring that BaZrS3is a promising candidate, these results potentially unleash the family of chalcogenide perovskites for optoelectronics such as photodetectors, photovoltaics, and light emitting diodes.