Dye-sensitized solar cells (DSSCs) with different thickness TiO2 nanoparticle films and a “double-layer” working electrode of TiO2 nanoparticle/TiO2 nanowire are fabricated. The influence of the TiO2 nanoparticle films thickness and of a light-scattering layer of TiO2 nanowire on the photovoltaic performance of DSSCs are investigated. The transport and interfacial transfer of electrons in DSSCs are investigated using intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS) to determine the lifetime, diffusion coefficient, and diffusion length of the electrons. The results indicate that the optimum TiO2 nanoparticle films' thickness for DSSCs is about 14 μm. The introduction of the light-scattering layer leads to an obvious enhancement of the power conversion efficiency. This can mainly be attributed to the superior light-scattering ability, fast electron transport, and long electron lifetime, resulting in a larger electron diffusion coefficient and a higher charge collection efficiency, which are confirmed by IMPS, IMVS, and EIS.

GaN is one of the third-generation broadband semiconductor materials developed rapidly in recent years, and Algan/GanHEMT has a broad application prospect in the fields of high temperature, high power, high frequency and radiation resistance, etc. In recent years, gallium nitride based high electron mobility transistors have been widely used in emerging industries, such as 5G technology, new energy vehicles, unmanned aircraft and other fields, due to their high power and high voltage resistance. However, due to the high power density of HEMT devices, the self-heating effect will lead to a significant increase in the junction temperature of the device, which will seriously affect the performance, reliability, and lifetime of the device. In this paper, the temperature characteristics of GaN high electron mobility transistors (GaN HEMTs) are studied, and the effect of self-heating effect on GaN HEMT devices is analyzed. In order to reduce the device temperature and improve the reliability of the device, a new device structure is proposed in this paper. The new structure replaces the conventional silicon and Si3N4 with highly thermally conductive diamond and SiC as the substrate and passivation layer of the device, which facilitates the heat dissipation from the substrate and passivation layer. Also, the new structure employs a hybrid barrier layer and field plate. Simulation results show that the new structure has about 30% lower temperature peak, 47% higher output current, 28% higher transconductivity, and up to 18.22% higher current collapse rate compared to the conventional structure.

Gallium nitride high electron mobility transistor (GaN HEMT) applications in high-power and high-frequency environments can lead to high device temperatures due to the self-heating effect, thus limiting device performance and reliability. In order to address this problem, this paper changes the material and structure of the device. It successfully reduces the maximum temperature of the device to 335 K by using a new structure of the diamond substrate, diamond heat sink layer, and InGaN insertion layer. Simulation results show that the new structure has a 35% reduction in maximum temperature, a 61% increase in current, a 37% improvement in maximum transconductance, and a 35% improvement in current collapse. At the same time, the new structure also improves the electron mobility of the channel.