Cadmium sulphide （CdS） and cadmium telluride （CdTe） thin films are deposited by electron beam evaporation. Atomic force microscopy （AFM） reveals that the root mean square （RMS） roughness values of the CdS films increase as substrate temperature increases. The optical band gap values of CdS films increase slightly with the increase in the substrate temperature, in a range of 2.42-2.48 eV. The result of Hall effect measurement suggests that the carrier concentration decreases as the substrate temperature increases, making the resistivity of the CdS films increase. CdTe films annealed at 300 ℃ show that their lowest transmittances are due to their largest packing densities. The electrical characteristics of CdS/CdTe thin film solar cells are investigated in dark conditions and under illumination. Typical rectifying and photovoltaic properties are obtained.
Nano-structured photon management is currently an interesting topic since it can enhance the optical absorption and reduce the surface reflection which will improve the performance of many kinds of optoelectronic devices, such as Si-based solar cells and light emitting diodes. Here, we report the fabrication of periodically nano-patterned Si structures by using polystyrene nano-sphere lithography technique. By changing the diameter of nano-spheres and the dry etching parameters, such as etching time and etching power, the morphologies of formed Si nano-structures can be well controlled as revealed by atomic force microscopy.A good broadband antireflection property has been achieved for the formed periodically nano-patterned Si structures though they have the low aspect ratio(<0.53). The reflection can be significantly reduced compared with that of flat Si substrate in a wavelength range from 400 nm to 1200 nm. The weighted mean reflection under the AM1.5 solar spectrum irradiation can be as low as 3.92% and the corresponding optical absorption is significantly improved, which indicates that the present Si periodic nano-structures can be used in Si-based thin film solar cells.
The detailed balance method is used to study the potential of the intermediate band solar cell （IBSC）, which can improve the efficiency of the gi-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar ceil with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shoekley-Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47070, having a better potential.
Si quantum dots （Si QDs）/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/ SiC stacked structures prepared in plasma enhanced chemical vapor deposition （PECVD） system. The micro- structures were examined by transmission electron micro- scopy （TEM） and Raman spectroscopy, and results demonstrate the formation of Si QDs. Moreover, p-i-n devices containing Si QDs/SiC multilayers were fabri- cated, and their photovoltaic property was investigated. It was found that these devices show the good spectral response in a wide wavelength range （400-1200 nm）. And it was also observed that by reducing the thickness of SiC layer from 4 to 2 nm, the external quantum efficiency was obviously enhanced and the short circuit current density （Jsc） was increased from 17.5 to 28.3 mA/cm2, indicating the collection efficiency of photo-generated carriers was improved due to the reduced SiC barriers.
Yun-Qing CAO Xin XU Shu-Xin LI Wei LI Jun XU Kunji CHEN
