Silicon Heterojunction Solar Cells Combining an a-Si:H (n) Electron-collector with a PEDOT:PSS Hole-collector

Abstract

We combine PEDOT:PSS as hole-selective layer on c-Si with a well-passivating electron-selective a-Si:H(n) layer in an alternative type of silicon heterojunction solar cell. As the interface between the PEDOT:PSS and the c-Si substrate plays a crucial role in the cell performance, we examine the impact of an interfacial SiOx tunneling layer between the c-Si substrate and the PEDOT:PSS in detail. We find that a natural SiOx layer grown within a couple of minutes leads to low J0 values ranging between (80 - 130) fA/cm2, allowing for Voc values of ∼690 mV. Implementation of this PEDOT:PSS/SiOx/c-Si junctions into solar cells with phosphorus-diffused n+ front results in low series resistance values of only 0.6 Ωcm2 and good fill factors >80% leading to efficiencies >20%. We then implement the PEDOT:PSS/SiOx/c-Si junction to the back of heterojunction cells with an a-Si:H(n)/ITO front, in order to demonstrate the feasibility of this novel cell concept, which has a higher Voc potential compared to cells with a conventionally processed front side. The cell efficiencies of the first batch reach 15.2%. This relatively moderate efficiency of the first cell batch is due to technological issues with the screen-printed front metallization grid, leading to poor fill factors of only 71%, whereas the Voc values of this first batch were already above 650 mV.