Photodetectors based on p-type metal oxides are still a challenge for optoelectronic device applications. Many effects have been paid to improve their performance and expand their detection range. Here, high-quality Cu1–x Ni x O (x = 0, 0.2, and 0.4) film photodetectors were prepared by a solution process. The crystal quality, morphology, and grain size of Cu1–x Ni x O films can be modulated by Ni doping. Among the photodetectors, the Cu0.8Ni0.2O photodetector shows the maximum photocurrent value (6 × 10–7 A) under a 635 nm laser illumination. High responsivity (26.46 A/W) and external quantum efficiency (5176%) are also achieved for the Cu0.8Ni0.2O photodetector. This is because the Cu0.8Ni0.2O photosensitive layer exhibits high photoconductivity, low surface states, and high crystallization after 20% Ni doping. Compared to the other photodetectors, the Cu0.8Ni0.2O photodetector exhibits the optimal response in the near-infrared region, owing to the high absorption coefficient. These findings provide a route to fabricate high-performance and wide-detection range p-type metal oxide photodetectors.

The band gap energy and optical constants are important parameters for solar cell design. Here, organic-inorganic hybrid halide perovskite CH 3 NH 3 PbI 3 films (about 140 nm thick) were prepared by vapor deposition at precursor solution temperatures of 30 °C, 50 °C, 70 °C, and 90 °C, respectively. By fitting the ellipsometric spectra in the photon energy range of 0.496-4 eV, we can find that the optical constants, absorption coefficients, and dielectric function strongly depend on the precursor temperature. Due to the change of electronic band structures and spin-orbit coupling, the band gap energy can be modulated from 1.634 eV to 1.516 eV with different precursor temperatures. As band gap energy increases, the Urbach energy decreases with each precursor temperature. The film with a precursor temperature of 70 °C shows the lowest Urbach tail energy (107 meV). The Urbach tail effects can be ascribed to the cumulative effect of impurities, the degree of disorder, and electron-phonon interaction. This study is helpful for understanding the intrinsic optical properties of perovskite films fabricated under different precursor temperatures, so as to provide important information for understanding the device physics and fabrication of high performance perovskite solar cells.

Effects of temperature on the optical properties of large-area ReS2 films (10 layers), which are prepared by chemical vapor deposition, have been investigated by Raman and reflectance spectra. The phonon frequencies of 18 Raman modes red-shift about 3 cm–1 by increasing the temperature from 140 to 320 K. The optical constants (n and k) at a photon energy region of 0.46–6.52 eV are obtained, and the values blue-shift with increasing temperature. Four interband transitions (E p1, E p2, E p3, and E p4) are observed at 1.53, 2.98, 4.25, and 5.37 eV at 303 K, respectively, and the values increase with increasing the temperature. The physical origins have been assigned to the different band-to-band direct electronic transitions. The optical band gap of the ReS2 films increases from 1.36 eV at 303 K to 1.38 eV at 383 K. Based on the first-principles calculation results, the band gap increases from 1.32 eV at a normal lattice constant to 1.40 eV at 1.1 times lattice constant. This is because the energy levels present the tendencies of degeneracy, due to which the coupling between the Re 5d orbital and S 3p orbital is weaker and the energy level splitting is smaller with increasing temperature.

CH3NH3PbI3 (MAPbI3) perovskite materials hold considerable promise for future low cost, high-efficiency solar cells, and replacement materials for toxic lead have also been in demand. In this study, the optical constants, absorption coefficients, and interband electron transitions of MAPb1−xSnxI3 (x = 0, 0.4, 0.8, and 1) films have been analyzed by spectroscopic ellipsometry in the photon range of 1 eV–5 eV. The bandgaps of MAPb1-xSnxI3 (x = 0, 0.4, 0.8, 1) are 1.54 eV, 1.51 eV, 1.49 eV, and 1.46 eV, respectively. With the increase in Sn, the s–p antibonding coupling becomes stronger, and the bandgap energy decreases, owing to the shallower and more active lone-pair states of Sn-5s than Pb-5s near the valence band maximum (VBM). According to the x-ray diffraction patterns, doping Sn does not change the material structures, which makes the shape of VBM more fluctuating, resulting in a similar band structure. Moreover, band structures and interband electron transitions of all four samples are discussed in terms of solid-state physics and can be assigned to the direct transition between the valence band and the conduction band at R, M, and X symmetry points.

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