Phosphorous Catalytic‐Doping of Silicon Alloys for the Use in Silicon Heterojunction Solar Cells

Abstract

Herein, the effectiveness of post-deposition catalytic-doping (cat-doping) on various doped silicon alloys, i.e., microcrystalline silicon (μc-Si:H), nanocrystalline silicon oxide (nc-SiOx:H), and microcrystalline silicon carbide (μc-SiC:H), for the use in silicon heterojunction solar cells is investigated. Phosphorous (P) profiles by secondary ion mass spectrometry (SIMS) reveal the P distribution and its difference in these three silicon alloy films. Conductivity and effective charge carrier lifetime of different samples are found to increase to different extents after cat-doping process. Coexistence of thermal annealing, hydrogenation, and phosphorus doping is confirmed by using different gases during the cat-doping process.

Phosphorus Catalytic Doping on Intrinsic Silicon Thin Films for the Application in Silicon Heterojunction Solar Cells

“…As discussed in our former work, the coexistence of thermal annealing, hydrogenation, and P doping effects during the Cat-doping process leads to the improvement in the passivation quality. Both the thermal annealing effect and hydrogenation effect during the process help to saturate the dangling bonds and therefore improve the passivation in the stack .…”

“…Former studies and this work have shown that Cat-doping on μc-Si:H and a-Si:H usually has larger N P and a larger penetration depth than that in c-Si. 25,27 It has also been found that the N P from Cat-doping is larger in c-Si with the (100) orientation than that in the (111) orientation, 35 where actually, thermal diffusion is also easier in the (100) than (111) wafers. 36 These studies give hints that the diffusion of P into silicon films during low T sub Cat-doping might depend largely on the defective microstructures of different silicon films.…”

“…Thus, the C s and N P decrease at a too high pressure. P Cat-doping has been confirmed to increase conductivity of silicon films; , however, the incorporated P atoms may not all be activated as dopants and the portion of activated P atoms is still under investigation.…”

“…Among many techniques to solve the aforementioned two problems, catalytic doping (Cat-doping) is a cheap, simple, and industrially feasible postdeposition doping method, which is based on the hot wire chemical vapor deposition (HWCVD) process . Doping gases, such as phosphine (PH 3 ) and diborane (B 2 H 6 ), are catalytically decomposed at the hot surface of the filaments into phosphorous (P) and boron (B) radicals. , The radicals move from the filament surface to the sample surface and then diffuse into the silicon material films, forming a shallow depth doping layer with a thickness of 5–20 nm. − Therefore, it is possible to replace the deposition of the doped silicon layer by Cat-doping on the intrinsic layer, which reduces the parasitic absorption of doped silicon layers. Former studies have shown that the material properties, such as conductivity and doping concentration, can be further tuned beyond the level that is achievable for as-grown films. ,, It has also been reported that the passivation quality of SHJ structures could be improved with Cat-doping on different interfaces, such as at the c-Si, a-Si:H­(i), and doped silicon layer surfaces in a SHJ structure. ,,,− …”

Enhancing the Selectivity and Transparency of the Electron Contact in Silicon Heterojunction Solar Cells by Phosphorus Catalytic Doping

“…In Figure 3c–e, the lower lifetime of the PECVD precursors compared to the reference is due to lack of field effect passivation. As discussed in our previous work, [ 40 ] the coexistence of thermal annealing and phosphorus doping in the Cat‐doping process could lead to an improvement in chemical passivation and field effect passivation, respectively. Since the thickness of the a‐Si:H(i) layer used in the passivation structure is thinner than the penetration depth of the P atoms, a shallow doped region should form on the surface of the c‐Si substrate, which could also act as a front surface field and improve the passivation.…”