Performance of Si/PEDOT:PSS Solar Cell Controlled by Dipole Moment of Additives

Solar cells composed of silicon (Si) and polymer films have attracted much attention because of their high performance and facile preparation using aqueous solutions. Although a large amount of research has been carried out to further improve their performance, the factors required to achieve this are not yet fully understood from the perspective of physical chemistry. Here, we show the effect of additives on the performance of Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells using six different additives. The relationships among the solar cell performance, electrical properties, and the structure of the polymer film are examined by changing the additive and conducting cyclic voltammetry, electric conductivity, and two-dimensional grazing incidence angle X-ray diffraction measurements. The dipole moment of the additive molecule was determined to be a key factor for improving the performance of Si/PEDOT:PSS solar cells. In particular, an additive with a higher dipole moment (μ > 3 D) caused an increase in the rate of charge diffusion and the ratio of face-on to edge-on structures of PEDOT molecules.