The a-Si:H/poly-Si Heterojunction Solar Cells

We present heterojunction solar cells with a structure of metal/a-Si:H (n-i-p)/poly-Si (n-p)/metal for the terrestrial applications. This cell consists of two component cells: a top n-i-p junction a-Si:H cell with wide-bandgap 1.8eV and a bottom n-p junction poly-Si cell with narrow-bandgap 1.1eV. The efficiency influencing factors of the solar cell were investigated in terms of simulation and experiment. Three main topics of the investigated study were the bottom cell with n-p junction poly-Si, the top a-Si:H cell with n-i-p junction, and the interface layer effects of heterojunction cell. The efficiency of bottom cell was improved with a pretreatment temperature of 900℃, surface polishing, emitter thickness of 0.43㎛, top Yb metal, and grid finger shading of 7% coverage. The process optimized cell showed a conversion efficiency about 16%. Top cell was grown by using a photo-CVD system which gave an ion damage free and good p/i-a-Si:H layer interface. The heterojunction interface effect was examined with three different surface states; a chemical passivation, thermal oxide passivation, and Yb metal. The oxide passivated cell exhibited the higher photocurrent generation and better spectral response.