Band Gap Optimization of CdTeSe Thin-Film Solar Cells

Device modeling and simulation studies of a CdTeSe thin film solar cell have been carried out. A variety of band-gap profiles, including ungraded, front graded, back graded, and double graded profiles of the CdTeSe absorber layer are examined and their performance characteristics have been analyzed. The calculation reveals that single junction cells with band-gap at the optimum value of 1.38 eV exhibit the maximum performance; alloys of CdTe and CdSe with a ratio of 1:1 forming CdTe0.5Se0.5 achieve the band-gap of 1.38 eV due to the bowing effect. The benefits of the band-gap grading are evaluated when the minimum band-gap is set at the optimum band-gap of 1.38 eV. It is shown that only few graded band-gap profiles exhibit an increase in efficiency, while most of graded profiles reduce performances

Subsurface Characteristics of Metal-Halide Perovskites Polished by Argon Ion Beam

Focused ion beam (FIB) techniques have been frequently used to section metal-halide perovskites for microstructural investigations. However, the ion beams directly irradiated to the sample surface may alter the properties far different from pristine, potentially leading to modified deterioration mechanisms under aging stressors. Here, we combine complementary approaches to measure the subsurface characteristics of polished perovskite and identify the chemical species responsible for the measured properties. Analysis of the experimental results in conjunction with Monte Carlo simulations indicates that atomic displacements and local heating occur in the subsurface of methylammonium lead iodide (MAPbI3) by glazing Ar+ beam irradiation (15 nm by 4 kV at 3 degree). The lead-rich, iodine-deficient surface promotes rapid phase segregation under thermal aging conditions. On the other hand, despite the subsurface modification, our experiments confirm the rest of the MAPbI3 bulk retains the material integrity. Our observation supports that polished perovskites could serve in studying the properties of bulk or buried junctions far away from the altered subsurface with care.Comment: six figure

Electronic, Energetic, and Chemical Effects of Intrinsic Defects and Fe-Doping of CoAl 2 O 4 : A DFT+U Study

The spinel cobalt aluminate has gained interest as a potential photoelectrochemical catalyst for the renewable production of hydrogen. Using band structure theory, we determine the energetics of possible intrinsic point defects in spinel CoAl 2 O 4 and analyze their effect on its electronic and chemical properties. Extrinsic Fedoping is also examined. Cation vacancies are found to be shallow acceptors, but their formation energy is sensitive to the growth conditions; an oxygen rich environment is required to enhance the p-type conductivity. Fe is an isovalent substituent on the Co (Al) site, exhibiting a preference for octahedral coordination, and forms a deep donor (acceptor) level near the center of the band gap, corresponding to a Fe(II) to Fe(III) transition