Antireflection and SiO<inf>2</inf> surface passivation by liquid-phase chemistry for efficient black silicon solar cells

Abstract

We report solar cells with both black Si antireflection and SiO 2 surface passivation provided by inexpensive liquid-phase chemistry, rather than by conventional vacuum-based techniques. The best cell efficiency from our first efforts was 16.4%. Nanoporous black Si antireflection on crystalline Si by aqueous etching promises low surface reflection for high photon utilization, together with lower manufacturing cost compared to vacuum-based antireflection coating. Agnanoparticle-assisted black Si etching and post-etching chemical treatment recently developed at NREL enables excellent control over the pore diameter and pore separation. Performance of black Si solar cells, including open-circuit voltage, short-circuit current density, and blue response, has benefited from these improvements. Prior to this study, our black Si solar cells were all passivated by thermal SiO 2 produced in a tube furnace. Although this passivation is effective, it is not ideal for ultra-lowcost manufacturing. In this study, we report, for the first time, the integration of black Si with a proprietary liquid-phase deposition (LPD) passivation from Natcore Technology. The Natcore LPD forms a layer of <10-nm SiO 2 on top of the black Si surface in a relatively mild chemical bath at room temperature. We demonstrate black Si solar cells with LPD SiO 2 with a spectrum-weighted average reflection lower than 5%, similar to the more costly thermally grown SiO 2 approach. However, LPD SiO 2 provides somewhat better surface-passivation quality according to the lifetime analysis by the photo-conductivity decay measurement. Moreover, black Si solar cells with LPD SiO 2 passivation exhibit higher spectral response at short wavelength compared to those passivated by thermally grown SiO 2 . With further optimization, the combination of aqueous black Si etching and LPD could provide a pathway for low-cost, highefficiency crystalline Si solar cells.Index Terms -black silicon, metal-assisted porous silicon etching, antireflection, liquid-phase deposition, surface passivation, photovoltaic cells.

SiO2Passivation Layer Grown by Liquid Phase Deposition for N-type Bifacial Silicon Solar Cells

“…Though its surface passivation effect is excellent, it requires expensive equipment, high growth temperature and a long process step. In consideration of the cost-effectiveness, liquid phase deposited (LPD) SiO 2 film [7][8][9][10] with high qualities may provide a good solution, which is also compatible with the present solar cell mass production. Yuan et al, [9] have first tried to use LPD SiO 2 film as the passivation layer of black silicon solar cells and acquired a conversion efficiency of 16.4%, showing the promising application of LPD SiO 2 film in silicon solar cells.…”

“…In consideration of the cost-effectiveness, liquid phase deposited (LPD) SiO 2 film [7][8][9][10] with high qualities may provide a good solution, which is also compatible with the present solar cell mass production. Yuan et al, [9] have first tried to use LPD SiO 2 film as the passivation layer of black silicon solar cells and acquired a conversion efficiency of 16.4%, showing the promising application of LPD SiO 2 film in silicon solar cells. He et al, [10] have also applied LPD SiO 2 passivation layer to polycrystalline silicon solar cells, but the passivation effect and the final conversion efficiency (5.61%) are not satisfying.…”

Enhanced Light Absorption and Minority Carrier Lifetime for Pn⁺ Multicrystalline Silicon by Treatment with HF/H₂O₂-Based Solutions

“…Though the SiN x coating film, fabricated by PECVD technology, can reduce the surface reflectance and give a high passivation to some extent on a large amount of front surface of mc-Si solar cells for mass production, it is helpless to the passivation on the deep trench structures because it is very difficult to be deposited on such deep and narrow trenches [2,3] . It has been reported that better passivation of mc-Si solar cells surface can be obtained by coating a thin SiO 2 layer between Si and SiN x [4][5][6][7] . However, thin SiO 2 can only solve the problem of passivation and yet useless for the problem of incident light-reflection losses.…”

“…However, the dramatically increased surface area of PS silicon might decreases the cell efficiency because of the increase of the surface recombination. One of the known technologies to solve this problem is to deposit a passivation layer, such as TiO 2 :Cr passivation layer [11] , vanadium oxide and SiO 2 [6] , into the PS structure.…”