Silicon remains the most widely employed material in solar cell due to the low cost, lack of toxicity, and small electronic band gap for near-infrared to visible light absorption. However, up to now, one of the main limitations of silicon solar cells is their high temperature and complex manufacturing processes. Recently, silicon solar cells hybridized with material like organic, semiconductor quantum dots, have attracted a great deal of research interest owing to their promise of room-temperature manufacturing and solution processing capability. But the problems of poor mobilities and toxicity need to be solved urgently. Fortunately, zero-dimensional graphene quantum dots (GQDs) have lately intrigued intensive interest in the field of energy and optoelectronic due to the tunable bandgap, emission in a range of visible light, longer hot carrier lifetimes, chemical stability and low toxicity. In addition to the low-cost and environment-friendly properties, GQDs could act as blocking layer to facilitate the separation of photo-generated electron-hole pairs and suppress the carrier recombination, thus increase the power conversion efficiency (PCE) in solar cells.

Here in, we present a solution-based, facile fabrication of silicon heterojunction solar cells using GQDs and poly(3,4-etyhlenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS). The PEDOT:PSS/n-Si cell showed a PCE of 8.86%, and the application of GQDs to the PEDOT:PSS/n-Si interface enhanced the PCE to 10.24%. The passivation of n-Si surface by quick annealing in vacuum at 500 °C for 10 min enhanced the PCE further to 11.77%. The quick processes for heterojunction formation and surface passivation would be well suited for low-cost fabrication of solar cells based on crystalline Si thin films.