Application Of Hole Selective Transport Layer In Back Junction Solar Cells

Constructing the dopant-free carrier-selective heterojunction by the energy band alignment,could effectively avert the high-temperature doping process flow in the traditional crystalline silicon solar cells(SCs),and thus suppress the parasitic absorption/Auger recombination losses that is inherent to the heavily doping.Recently,this newly concept has become one of the most hot topics in the photovoltaics field.In this paper,we review two representative dopant-free hole-selective transport materials,i.e.,poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) and molybdenum oxide(MoO_x),and address their effects of the photoelectric parameters on the device performance when they are integrated in the rear side of Si SC to form back contact heterojunction.The main contents and the demonstrated results are shown as follows:(1)We demonstrate a thickness-dependent passivation effect and investigate their photoelectric characteristic parameters via fabricating the corresponding devices,yielding the optimal efficiency under the PEDOT:PSS thickness of 200 nm.(2)The thick PEDOT:PSS film with high passivation effect could receive a high efficiency because the parasitic absorption of the spin-coated PEDOT:PSS film can be alleviated when they were deposited on the rear side of Si surface.By screening PEDOT:PSS thickness,an excellent efficiency of 16.3%can be achieved.The implement of the mild chemical pretreatment could further improve the efficiency of this type of SCs to 16.8%.Moreover,the back-side PEDOT:PSS design shows a better long-term stability than the traditional front-side one.(3)The MoO_x film as the hole-selective transport layer was applied in the back side of Si SCs.With the presence of an intrinsic hydrogenated amorphous silicon[a-Si:H(i)]film between Si and MoO_x film,the passivation performance of the related devices could be improved and the carrier recombination in the rear side junction area could be reduced.By further designing on the passivation properties and contact resistances,a high efficiency of 16.7%can be obtained.In this study,the thickness-dependent passivation quality of the PEDOT:PSS film on silicon wafer and the method of the improved passivation quality for MoO_x film were studied,which provides a simply and effective approach to pursue a high efficiency polymer/silicon and transition metal oxide/silicon SCs.