The effects of nano/micro-scale hierarchical structures on the performance of silicon/organic heterojunction solar cells

In this paper, we identify the role of the nano/micro-scale hierarchical structures on the performance of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/Si heterojunction solar cells (HSCs). The balance of light trapping and electrical contact between PEDOT:PSS film and structured Si substrates can be ameliorated via a suitable surface modification of hierarchical structures, resulting in increasing the short-circuit current density, open-circuit voltage and fill factor. The effect of surface adhesion for hierarchical structured surfaces with PEDOT:PSS film is investigated. It is clearly found that the power conversion efficiency (PCE) of silicon/organic HSCs can be remarkably increased with the help of enhanced adhesion between PEDOT:PSS film and hierarchical structured Si surfaces via a chemical cross-linkable silance. The optimized HSCs with the hierarchical structures, which are made up of nanowires growing on micro-scale pyramids, can attain a high PCE of 12.2%, which is greater than the planar and pyramid HSCs. The results reveal that the equilibrium of light trapping and electrical contact between PEDOT:PSS film and structured Si substrates is a key factor to improve the electrical performances of the hierarchical structured HSCs. Meanwhile, it is found that the hierarchical structured HSCs are less sensitive to the incident angle than the HSCs with pyramid structured surfaces. Furthermore, the impact of temperature affecting the PCE of the silicon/organic HSCs is investigated and the results demonstrate that the HSCs with hierarchical structured surfaces have a higher PCE than that with planar and pyramid ones when considering the temperature effects. This work reveals a proper trade-off between the ability of light trapping and carrier collection for nano/micro-structures to improve the performance of PEDOT:PSS/Si HSCs.