[en] This paper reports the doping effect of cholesteric liquid crystal 3 β -Hydroxy-5-cholestene 3-oleate on polymer solar cells composed of the poly 3-hexyl thiophene and the fullerene derivative. With a doping ratio of 0.3 wt%, the device achieves an ideal improvement on the shunt resistor and the fill factor. Compared with the reference cell, the power conversion efficiency of the doped cell is improved 24%. The photoelectric measurement and the active layer characterization indicate that the self-assembly liquid crystal can improve the film crystallization and reduce the membrane defect. (special topic)

[en] Highlights: • A computational method for predicting birefringence of LC in THz range was provided. • The birefringence of 5CB were calculated using Gaussian09 software. • The influence of functional and basis sets on birefringence has been evaluated. This letter provides a computational method for predicting birefringence of nematic liquid crystal (LC) in the terahertz band. Using Vuks’ approximation and Haller's approach combination with density functional theory (DFT) and time-dependent density functional theory (TDDFT) method, we calculated the frequency and temperature dependence refractive indices and birefringence of LC 5CB in a frequency range 0.2–1.0 THz. The greater agreement between calculated results and experimental values indicates that this is an applicable method to predict optoelectronic properties of LC materials in THz band. The present work gives a useful guide to screen or design LC molecules for THz applications.