The Analysis Of A-Si/c-Si Heterojunction Solar Cell Performance

Solar energy is favored by people for its excellent characteristics of renewable and none polluting. Solar cell is a kind of photovoltaic device which can convert solar energy into electrical energy. There are many kinds of solar cells, among which the a-Si /c-Si heterojunction solar cell is particularly attractive because of its unique performance.Battery structure has an important influence on the performance of a-Si /c-Si heterojunction solar cells. The battery of TCO/a-Si(p) /a-Si(i) /c-Si(n) /a-Si(n+) / TCO structure is simulated and the results show as follows. Firstly, the cell performance of pyramid–type surface is better than the flat-type. Secondly, changes of work function in the upper and lower surface transparent conductive oxide(TCO) film can lead to changes of battery performance, which is affected by a question whether the direction of electric field formed by adjacent semiconductor material is consistent with the direction of built-in electric field of P-N junction. That indicates the battery performance can be improved by the same direction, otherwise reduced. Thirdly, the increase of the window layer thickness can degrade the performance of the battery, which is mainly affected by the quantum efficiency of the short-wave area. Although increasing of the doping concentration can enhance cell efficiency in a certain range, at the same time it also increases the carrier recombination probability in the window layer, which can lead to the decline in the level of short-circuit current. Increasing of the window layer band gap results in rising of valence band offset and then lowers the collection rate of hole decrease, which reduces the battery efficiency. Then the difference of the solar cell conversion efficiency whether having intrinsic layer is as high as 3.21%, which indicates that the intrinsic layer is very effective for the interface passivation. Increasing of the intrinsic layer thickness can drop the quantum efficiency of short wave, that is to say, the reduction of the battery efficiency. At last, the difference of the solar cell conversion efficiency whether having back surface field(BSF) is as high as 4.4%. In the region of the substrate, the number of minority carriers hole for cell with back surface field are more than cell without back surface field, which illustrates that back reaction of back surface field is very effective for cell.Band matching has an important role in solar cells. By simulating solar cell of TCO/ a-Si:H(n)/ a-Si:H(i)/c-Si(p)/?c-Si(p+)/Ag, certain consequences can be found as follows. The battery performance could be affected by the matching of TCO work function and the window layer band gap. The best combination values for TCO work function and window layer band gap are 4.2eV and 1.95 eV. The interface states between intrinsic layer and substrate can reduce the solar cell performance. However increasing of the valence band offset between them can weak the effect of interface state for solar cell performance. That the back surface field affects battery performance is not achieved by changing the proportion of the conduction band offset and valence band offset, but by increasing the number of minority carriers(electron) on the electric field.