The Research On Surface And Interfacial Characteristics Of Photovoltaic Devices

The performance of semiconductor devices is not only related to materials, but also influenced by the surface and interfacial characteristics of devices. As a typical semiconductor device, the performance of photovoltaic device is influenced by both the movement of carrier and optical properties of surface and the interface. The research on surface and interfacial characteristics of photovoltaic devices has important meaning for both optimizing structure of photovoltaic device and improving the conversion efficiency. Specific researches were done as followed:For the surface, a simple low temperature surface passivation method based on high pressure O2thermal oxidation was proposed for nano-silicon solar cells. With this method, the nanowire textured surface of the black silicon solar cells can be effectively passivated at an extremely low temperature of～450℃, under which the prototype structure of the device would not be damaged and a better performance was achieved compared with that treated with the conventional high temperature surface passivation. Then, the current-voltage (I-V) measurement and external quantum efficiencies (EQEs) measurement were applied to characterize the electrical properties of different devices. By contrast, we found that high-pressure oxidation surface treatment technology could effectively reduce the recombination effect and in the wavelength range of350～700nm, the EQEs were improved. Finally, the conversion efficiency of nano-silicon solar cells has reached12.22%. In addition, high-pressure technique was also applied to the process of annealing treatment and improved the surface properties of photovoltaic materials. Annealing studies were performed to investigate the effects of heat treatment on InN thin films by changing the annealing condition from vacuum to high pressure N2. Then, Kelvin probe technique, an effective characterization method was applied to characterize the changes of surface work function, which arranged from4.8eV to5.2eV with different treatment environments.For the interface, both planar-Si and nano-Si were used as substrates for different heterojunctions. The differences in electrical properties between heterojunctions were compared and the effects of the interface on the device performance were explored. In the process of I-V measurement, we found that there existed big differences between heterojunction devices with different interracial morphologies. In order to further explore the mechanism, impedance spectroscopy (IS) measurement was carried out and fitting process were bone by creating an equivalent circuit which corresponded to the structure of the devices. In the process of fitting, the big differences between device parameters were found, which were induced by defect states and parasitic effects at the interface of heterojunctions. Then, we carried out the transient spectrum photovoltaic (TPV) measurement and got the effective life time of devices with different interfacial morphologies, which further prove that defect states and parasitic effects at the interface had effect on performance of device.