Transparent low resistivity CdS films have been evaporated on p-Si and n-p Si monocrystalline substrates to form heterojunction solar cells. Electrical and optical properties are investigated by I-V, C-V and quantum efficiency measurements. By comparing to conventional n-p Si cells, it is found that CdS/n-p Si configuration has the advantage of homojunction cells with a high V$ sb{ rm oc}$, and the advantage of heterojunction cells with a high I$ sb{ rm sc}$. The high V$ sb{ rm oc}$ is due to the electrical property domination of the homojunction of this configuration and the high I$ sb{ rm sc}$ is due to more electron-hole pairs excited by high energy photons at or near the homojunction of this configuration. Effects of interface states on heterojunctions is also studied. Frequency dispersion on capacitance is observed on CdS/p-Si cells. The dispersion is due to the lattice mismatch between CdS and Si which introduces high densities of interface state. The densities of interface state and the relaxation time constant are calculated. The cause of dispersion can be determined by doing capacitance measurements at low temperature so that trap level effect is eliminated. No significant dispersion is observed on CdS/n-p Si cells. It further confirms the electrical property domination of the homojunction of the CdS/n-p Si cells.

Shih, I. (Supervisor)