Simulation Study On Single Junction Microcrystalline Silicon And Micromorph Solar Cells

Hydrogenated microcrystalline silicon (μc-Si:H) thin film solar cells have got more attention among the second generation solar cells for the advantages of high stability and low cost. In addition, uc-Si:H thin film with the bandgap of l.leV, is an idea partner for hydrogenated amorphous silicon (a-Si:H) to combine a-Si:H/μc-Si:H tandem cells. The device can not only extend the spectral response of a-Si:H solar cells to near infrared light, but also suppress the light-induced degradation, so it is one of the most promising candidates among the third generation solar cells.For a better understanding of electronic transport mechanisms and optimize structure in silicon-based film solar cell, in order to improve the photoelectric conversion efficiency. The performance of single junctionμc-Si:H and a-Si:H/μc-Si:H tandem cell are studied by AMPS-1D, which was developed by the University of Pennsylvania in US. The characteristics of intrinsic layer(i layer) is the key factor that influence the performance of pinμc-Si:H solar cell. Besides, the effects of each interface, especially p/i characteristics, inside solar cell on solar cell cannot be ignored. So the effects of crystallinity of the intrinsic layer and p/i characteristics on performance parameters of (μc-Si:H solar cell are studied. For tandem solar cell, current match of solar cell is crucial. Based on the simulation of single junction solar cell, the effects of the thickness of a-Si:H top cell andμc-Si:H bottom cell and intermediate reflector layer on performance parameters of a-Si:H/μc-Si:H tandem cell are further studied. The main conclusions of this paper are as follows:(1) With the increase of crystallinity of the i layer Ic, the open circuit voltage Voc ofμc-Si:H thin film solar cells decreases monotonously, the short circuit current Jsc and fill factor FF increase first and then decrease. Photoelectric conversion efficiencyηreaches a maximum when Ic is between 30% and 60%, which is consistent with the experimental result.(2) With the increase of p/i interface defect state density (NtP/1), the open circuit voltage Voc and fill factor FF decrease monotonously, the short circuit current Jsc almost remains constant. The results ndicate that the p/i interface defect state density is the major reason contributed to performance differences ofμc-Si:H solar cells with intrinsic layer prepared by PECVD and HWCVD.(3) With the increase of the thickness of amorphous incubation layer of p/i interface, short circuit current Jsc,fill factor FF decrease monotonously, while the open circuit voltage Voc increases, and photoelectric conversion efficiencyηdecrease rapidly.(4) As for a-Si:H/μc-Si:H tandem cell, when the thinkness of bottom cell (dibot) is fixed, short circuit current Jsc andηincrease first and then decrease with the increase of top cell thickness, andηreaches a maximum when the optimum current match is obtained; Maximum efficiencyηmax is improved when the thinkness of bottom cell increases within a certain range, but the thinkness of top cell also increases; Best current matching requires 250nm top cell thinkness when the thinkness of bottom cell is 1.5μm.(5) Photo current of top cell is improved effectively when intermediate reflectors layer is introduced between a-Si:H top cell andμc-Si:H bottom cell, while photo current of bottom cell reduces simultaneously; When the thinkness of bottom cell (dibot) is fixed, the thinkness of top cell decreases and stability of tandem cell improves via the introduction of intermediate reflectors layer; when the thinkness bottom cell is 1.5μm, best current matching requires 200nm top cell thinkness as a result of the introduction of ZnO intermediate reflectors layer.(6) Refractive index n of intermediate reflectors layer has an important effect on current match of tandem cell when the thinkness of intermediate reflectors layer is fixed, and reflection effects is the best as n is far less than refractive index of silicon-based film.