Abstract
In this work, n-type silicon based solar cells with WO3/Ag/WO3 multilayer films as emitter (WAW/n-Si solar cells) were presented via simple physical vapor deposition (PVD). Microstructure and composition of WAW/n-Si solar cells were studied by TEM and XPS, respectively. Furthermore, the dependence of the solar cells performances on each WO3 layer thickness was investigated. The results indicated that the bottom WO3 layer mainly induced band bending and facilitated charge-carriers separation, while the top WO3 layer degraded open-circuit voltage but actually improved optical absorption of the solar cells. The WAW/n-Si solar cells, with optimized bottom and top WO3 layer thicknesses, exhibited 5.21% efficiency on polished wafer with area of 4 cm2 under AM 1.5 condition (25 °C and 100 mW/cm2). Compared with WO3 single-layer film, WAW multilayer films demonstrated better surface passivation quality but more optical loss, while the optical loss could be effectively reduced by implementing light-trapping structures. These results pave a new way for dopant-free solar cells in terms of low-cost and facile process flow.
Highlights
Silicon based heterojunction (SHJ) solar cells with 24.7% power conversion efficiency (PCE) has been substantiated by Panasonic,[1] which implementing high quality intrinsic a-Si:H as passivation layer and B2H6 doped a-Si:H as emitter
The results indicated that the bottom WO3 layer mainly induced band bending and facilitated charge-carriers separation, while the top WO3 layer degraded open-circuit voltage but improved optical absorption of the solar cells
We develop a novel solar cell structure using WAW multilayer as emitter on n-type silicon (WAW/n-Si solar cells), neither any TCO film nor any post-deposition annealing is employed in device fabrication process
Summary
Silicon based heterojunction (SHJ) solar cells with 24.7% power conversion efficiency (PCE) has been substantiated by Panasonic,[1] which implementing high quality intrinsic a-Si:H as passivation layer and B2H6 doped a-Si:H as emitter. In the last few years, MoO3, WO3, V2O5 with nm-thickness capped directly on n-type silicon (n-Si) show extraordinary hole-selectivity,[14,15] which favour charge-carriers’ separation by transporting holes while blocking electrons, and reaching the efficiency of 14.3% for MoOx/n-Si heterojunctions.[14] when inserting an intrinsic a-Si:H layer into MoOx/n-Si heterojunctions for passivation, PCE as high as 22.5% has been recorded for this novel structure (MoOx/a − Si:H/n-Si) solar cells.[12] Analogously, TiO2 exhibits superior electron-selective and surface passivation property,[8,9] proving dopant-free TMOs are ideal candidates for replacing doped a-Si:H. and collection. We compare the electrical and optical performance of WAW multilayer and WO3 layer in terms of application in silicon based solar cells
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