Role of thickness on spray coated PEDOT:PSS thin film properties for bulk heterojunction organic solar cell

Spray deposited poly (3,4 ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is used as a hole transport layer (HTL) at different thickness. These HTL layer is characterized in terms of structural and electrical properties. The thickness of HTL layer is varied from 40 to 120 nm by altering deposition time from 20 to 60 sec. The lowest thickness HTL in 20 sec deposition time is not efficient because the small droplets after atomization was dried very quickly before spreading and complete merging on the hot surface producing voids which affects the photovoltaic outcomes. The optical microscopy images revealed that an improvement in the morphology of PEDOT:PSS layer with increased film thickness from 40 to 80 nm due to better packing density. On further increasing the spray time from 40 to 60 sec HTL thickness increases to 120 nm, consequently absorbance of HTL increased which diminishes the performance of the devices. The roughness of PEDOT:PSS layer is observed minimum for 80 nm thickness HTL. The bulk heterojunction organic solar cells (OSCs) with conjugated polymers PTB7 and PC71BM on the HTL of spray coated PEDOT:PSS of is fabricated. The power conversion efficiency (PCE) observed maximum for 80 nm thick HTL due to the optimal surface morphology with least surface roughness and good transparency.