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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.

Doping is an effective strategy for controlling the charge density and device performance of thin‐film electronics. Herein, a new doping system is reported for organic electronics using the organic salt p‐dopant N,N‐dimethylanilinium tetrakis(pentafluorophenyl)borate (DTB) to significantly improve the device performance of indacenodithiophene‐co‐benzothia‐diazole (IDT‐BT) organic field‐effect transistors (OFETs). With optimized doping ratios, the hole mobility increases almost fourfold from 0.32 to 1.15 cm2 V–1 s–1 and the threshold voltage reduces from −38  to 0 V. Moreover, systematical electrical characterizations demonstrate that the contact resistance and activation energy dramatically reduce in the doped devices. Such reductions are ascribed to the shift of the Fermi energy level closer to the transport level and the lowered density of trap states in doped semiconductors, as revealed by ultraviolet photoelectron spectroscopy and low‐frequency noise measurements, respectively. This study also demonstrates that the trap density increases when the doping ratio is high, explaining the device performance degradation at high doping ratios. This is the first time that DTB organic salt is used as an efficient dopant to improve the performance of OFETs, demonstrating a promising route for employing organic salt dopants to achieve high‐performance OFETs.