Influence of solution heating on the properties of PEDOT:PSS colloidal solutions and impact on the device performance of polymer solar cells

摘要

We have investigated the effects of temperature variation on colloidal solutions of the electrode polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) and its consequences for photovoltaic devices using conjugated polymer blends as the photoactive material. By variation of the PEDOT:PSS solution temperature between 20 and 90 °C we observed reversible temperature-dependent change in size of the PEDOT:PSS particles. This process is associated with temperature and concentration dependent phase transitions of the PSS electrolyte chains. We found optimum device performance, in particular high quantum efficiency and power conversion efficiency for solar cells, with PED-OT:PSS layers produced from 70 °C solutions. After consideration of film morphology, particle size, conductivity and work function, we conclude that improved device performance originates from enhanced conductivity in films deposited from heated solutions. While film conductivity increases monotonically with solution temperature, devices produced using solution temperatures greater than 70 °C suffer from the increased work function of the PEDOT:PSS layer.