Potential of PEDOT:PSS as a hole selective front contact for silicon heterojunction solar cells

Sara Jäckle,Klaus Jäger,Klaus Lips,Martin Liebhaber,Clemens Gersmann,Mathias Mews,Silke Christiansen

doi:10.1038/s41598-017-01946-3

Sara Jäckle, Klaus Jäger + Show 5 more

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https://doi.org/10.1038/s41598-017-01946-3

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We show that the highly conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) can successfully be applied as a hole selective front contact in silicon heterojunction (SHJ) solar cells. In combination with a superior electron selective heterojunction back contact based on amorphous silicon (a-Si), mono-crystalline n-type silicon (c-Si) solar cells reach power conversion efficiencies up to 14.8% and high open-circuit voltages exceeding 660 mV. Since in the PEDOT:PSS/c-Si/a-Si solar cell the inferior hybrid junction is determining the electrical device performance we are capable of assessing the recombination velocity (vI) at the PEDOT:PSS/c-Si interface. An estimated vI of ~400 cm/s demonstrates, that while PEDOT:PSS shows an excellent selectivity on n-type c-Si, the passivation quality provided by the formation of a native oxide at the c-Si surface restricts the performance of the hybrid junction. Furthermore, by comparing the measured external quantum efficiency with optical simulations, we quantify the losses due to parasitic absorption of PEDOT:PSS and reflection of the device layer stack. By pointing out ways to better passivate the hybrid interface and to increase the photocurrent we discuss the full potential of PEDOT:PSS as a front contact in SHJ solar cells.

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Efficient solar cells are often based on heterojunctions, providing charge selective contacts to the absorber material
The bulk-limited solar cell with the lower quality Si wafer (L ≪ d) has a VOC of 544 mV and a power conversion efficiency (PCE) of 12.2%. This compares well to earlier results, where we showed in detail that for the here used Si wafer device performance depends on crystalline n-type silicon (c-Si) bulk lifetime and not on the hybrid front junction, proving that PEDOT:poly(styrene sulfonate) (PSS)/c-Si cannot be considered as a metal-semiconductor junction[16]
By combining a PEDOT:PSS front junction on c-Si with a superior amorphous silicon (a-Si) back contact, we present a solar cell with an efficiency of 14.8% and an open-circuit voltage (VOC) of 663 mV

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Efficient solar cells are often based on heterojunctions, providing charge selective contacts to the absorber material. We investigate the limitations of PEDOT:PSS as a hole selective front junction in hybrid SHJ solar cells by combining it with a superior, highly electron selective and well passivated, back contact on a Si wafer with a long bulk lifetime. For this we deposit a layer stack of intrinsic and n+-doped hydrogenated amorphous silicon (a-Si:H), adopted from the high efficiency SHJ technology, on the backside of the wafer.

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