Partially Passivated Micro-pyramidal Silicon/ PEDOT:PSS Hybrid Solar Cells with high efficiency

Abstract

Organic/inorganic hybrid solar cells can be attractive owing to the synergetic advantages of the high carrier mobility and efficiency from inorganic semiconductors and the simple process and low cost from organic semiconductors. Especially in case of Si/PEDOT:PSS hybrid solar cells, PEDOT:PSS acts as a hole-transport layer with high transparency and conductivity and enhances the efficiency of the solar cell. However, when PEDOT:PSS is applied to the micro-pyramidal Si surface to improve the light absorption, the conformal coating becomes very challenging due to the networking of long polymer chains. Namely, PEDOT:PSS tends to cover only the tip areas of micro pyramids instead of whole Si surfaces including deep valleys of Si micro pyramids, which causes the degradation of the hybrid solar cells because the uncovered Si surface acts as surface recombination centers as well as they are not contributing the separation of photo-excited electron-hole pairs. In this work, we suggest a novel local SiN passivation technique around the valleys of Si micro pyramids. The SiN passivation layer was synthesized by plasma-enhanced chemical vapor deposition. For the local passivation, we spin-coated photoresist (PR) on a micro-pyramidal SiN/Si surface, followed by two-step soft and hard baking at 85 °C and 110 °C, respectively. During the soft baking, PR flows towards the valleys of micro pyramids resulting in non-uniform PR coating thickness between the tip and valley areas. Because of the non-uniform PR thickness, we could obtain a partially-passivated Si surface after a chemical etching of the SiN layer using a buffered-oxide etchant (BOE). The Si/PEDOT:PSS hybrid solar cells are fabricated by a spin-coating of PEDOT:PSS on a partially-passivated micro-pyramidal Si surface, followed by a annealing at 130 °C. The partially-passivated hybrid solar cells were demonstrated to have an enhanced power conversion efficiency, compared with the sample without the partial-passivation layer. This is due to the enhancement of minority carrier lifetime or lower surface recombination velocity as well as the anti-reflection effect of the remaining SiNx layer around the valley area of Si micro pyramids.