Greatly enhanced hole collection of MoO_x with top sub-10 nm thick silver films for gridless and flexible crystalline silicon heterojunction solar cells

Abstract

Greatly enhanced hole collection of MoOx is demonstrated experimentally with a top sub-10 nm thick Ag film. With this hole-selective contact, a 50 μm thick gridless c-Si solar cell, showing excellent flexibility, is 75% thinner but 86% efficient.

Highly Efficient and Highly Flexible Thin Crystalline Silicon Heterojunction Solar Cells Based on Dopant-Free Carrier-Selective Contacts Fabricated with Simple Processes

“…The PCE of the 25 μm thick solar cell is well above 90% of the initial value of the unbent solar cell even when r is as small as 4 mm. In comparison to the gridless solar cell reported previously, the solar cells reported in this work show much better mechanical flexibility, mainly because the inner grid electrode, uncracked during the mechanical bending, can efficiently collect the photoholes.…”

“…The good carrier collection ability of the ITO layer is obviously the dominant reason for the significant increment in FF of the solar cell. On the basis of our previous work, the passivation effect of the MoO x layer would be weakened slightly with a lower minority carrier lifetime when ITO was sputtered. Therefore, V oc decreases slightly for the ITO solar cell.…”

“…Fortunately, J sc does not degrade much, i.e., by only 1.63, 5.16, and 12.63% when the c-Si thickness ( t Si ) is reduced by 77.5, 82.5, and 87.5% from 200 μm to 45, 35, and 25 μm, respectively (Figure b and Table ). On the basis of our previous experience, − the etched thin wafers always have rough surfaces. The 45 and 200 μm thick c-Si wafer surfaces are shown in Figure S2 of the Supporting Information.…”

“…Nevertheless, the above issues with doped contacts still occur and become more serious for thin solar cells. Only a few reported thin c-Si solar cells were based on undoped HSCs and ESCs. − Using PEDOT:PSS as the HSC and Al as the ESC, He et al reported a 20 μm thick c-Si solar cell and achieved a PCE as high as 12.2% . Then, they replaced the Al back ESC with a passivating one based on TiO x /LiF x /Al and achieved a 25 μm thick c-Si solar cell with its PCE up to 15.1% .…”

“…Then, they replaced the Al back ESC with a passivating one based on TiO x /LiF x /Al and achieved a 25 μm thick c-Si solar cell with its PCE up to 15.1% . These reports show the great potential of thin c-Si solar cells with dopant-free contacts, whose PCEs are however still below 10% universally, − far below the PCEs of their counterparts with doped contacts. − Besides the cost reduction, reducing the c-Si wafer thickness could also deliver mechanical flexibility, which is another unique advantage of thin c-Si solar cells. ,,,,,− …”