Multifunctioning graphene oxide capping layer for highly efficient and stable PEDOT:PSS–silicon hybrid solar cells†

Abstract

Hybrid heterojunction solar cells (HHSCs) of an organic conjugate polymer, namely, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and silicon have received extensive attention due to their high efficiency (PCE) and low-temperature processing. However, effective collection of charge carriers from the PEDOT:PSS/n-Si interface is a challenging task due to various defects and low band offset at the interface. The current study explores ways of overcoming the limitations of HHSCs and unveils the potential of solution-processed graphene oxide (GO) thin capping layer for achieving high-efficiency and stable PEDOT:PSS/n-Si HHSCs. It also unveils the GO-induced tuning of the band bending at the interface and thus improved carrier selection. Moreover, it facilitated improved charge transportation in the PEDOT:PSS via screening the PEDOT–PSS interaction, as evidenced by a significant improvement (>2-fold) in the electrical conductivity of the PEDOT:PSS layer after applying the GO layer. The integration of the GO capping layer reduced the optical reflection to <8% and enhanced the Si surface passivation by >2 fold. The cumulative effect of GO capping led to a ∼2.4% absolute enhancement in the PCE with respect to the device without any GO layer. The champion GO/PEDOT:PSS/n-Si HHSCs exhibited a PCE of 11.66% in a simple device design on a low-cost solar-grade Si wafer. Moreover, the GO capping facilitated environment protection to the PEDOT:PSS, increasing the stability of the device under atmospheric conditions, thus revealing the great potential of the thin GO layer for highly efficient and stable HHSCs.