Abstract
We have investigated the influences of diverse physical parameters on the performances of a silicon homo-heterojunction (H-H) solar cell, which encompasses both homojunction and heterojunction, together with their underlying mechanisms by the aid of AFORS-HET simulation. It is found that the performances of H-H solar cell are less sensitive to (i) the work function of the transparent conductive oxide layer, (ii) the interfacial density of states at the front hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) interface, (iii) the peak dangling bond defect densities within the p-type a-Si:H (p-a-Si:H) layer, and (iv) the doping concentration of the p-a-Si:H layer, when compared to that of the conventional heterojunction with intrinsic thin layer (HIT) counterparts. These advantages are due to the fact that the interfacial recombination and the recombination within the a-Si:H region are less affected by all the above parameters, which fundamentally benefit from the field-effect passivation of the homojunction. Therefore, the design of H-H structure can provide an opportunity to produce high-efficiency solar cells more stably.
Highlights
Amorphous silicon/crystalline silicon (a-Si/c-Si) heterojunction solar cells have attracted considerable attention in the recent decade, mainly due to their small temperature coefficient, simple fabrication process and high open-circuit voltage (V OC) benefitted from the large difference in Fermi energy of the two materials.[1,2,3,4,5] In order to passivate the c-Si surface, a thin intrinsic hydrogenated amorphous silicon (i-amorphous silicon/crystalline silicon (a-Si):H) layer is generally inserted between the doped a-Si layer and the c-Si substrate, forming the heterojunction with intrinsic thin layer (HIT) solar cells
Lots of investigations have indicated that inappropriate work function of the transparent conductive oxide (TCO) layer will lead to a dramatical degradation of the performances of HIT solar cells, because the band bending in the emitter strongly depends on the work function of the TCO layer and the emitter.[7,8,9,10,11]
work function of TCO layer (WFTCO) has been considered as a crucial factor in a-Si/c-Si heterojunction solar cells due to the fact that WFTCO determines the electrical TCO/p-type a-Si:H (p-a-Si):H Schottky contact properties and the band bending in the a-Si:H/c-Si junction region.[8,27,28]
Summary
Amorphous silicon/crystalline silicon (a-Si/c-Si) heterojunction solar cells have attracted considerable attention in the recent decade, mainly due to their small temperature coefficient, simple fabrication process and high open-circuit voltage (V OC) benefitted from the large difference in Fermi energy of the two materials.[1,2,3,4,5] In order to passivate the c-Si surface, a thin intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer is generally inserted between the doped a-Si layer and the c-Si substrate, forming the heterojunction with intrinsic thin layer (HIT) solar cells. We have previously presented that the silicon homo-heterojunction (H-H) solar cell, which simultaneously contains homojunction and heterojunction, exhibits better tolerance for the interfacial DOS as compared to the HIT solar cell by AFORS-HET simulation.[21] In addition, it was found that the H-H solar cell shows a much higher fill factor (FF). With these two advantages, even if considering the fact that the interfacial DOS of the H-H solar cell is much higher, for example two magnitudes higher, the H-H solar cell can still realize the efficiency as high as that of the HIT solar cell but has a better stability. We identify that the physical origins behind the advantages of the H-H solar cell are the decreased interfacial recombination and the reduced recombination within the a-Si:H region, which are fundamentally ascribed to the field-effect passivation from the homojunction
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