Lower Drying Temperature Process for Hole Transport Layer PEDOT: PSS in PCDTBT: PCBM Devices

Water soluble PEDOT:PSS is a popular choice for hole transport layer (HTL) in organic photovoltaic (OPV) cells. However, the process conditions to form HTL with PEDOT:PSS has to be re-optimised when using it in OPV devices where the photoactive layer (PAL) polymer may be adversely affected by the 100 °C PEDOT:PSS drying temperature. In this paper, PCDTBT:PCBM blend devices formed with PEDOT:PSS HTL drying temperature on a hot plate of 70 °C, instead of the conventional 100 °C, is shown to result in superior solar cell performance. Devices using 70 °C drying temperature for PEDOT:PSS are shown to be superior in exciton harvesting; have a smoother PEDOT:PSS surface; have lower traps in the device PAL; and exhibit an overall increase in power conversion efficiency compared to devices using the conventional 100 °C PEDOT:PSS drying process. However, PEDOT:PSS drying carried out in a vacuum chamber at 70 °C results in significant degradation of the OPV device.