Effect of ultraviolet–ozone on ITO/P3HT interface for PEDOT:PSS-free polymer solar cells

A simple device structure of bulk hetero-junction polymer solar cells (PSCs) with poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (P3HT:PCBM) is demonstrated without poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS). Ultraviolet (UV)–ozone treatment alters the surface atomic compositions making it oxygen rich and carbon deficient. These chemical changes increase the workfunction of indium tin oxide (ITO) by 0.2 eV. The ITO anode with high workfunction results in efficient hole collection at ITO/P3HT interface. This method makes it possible to eliminate PEDOT:PSS with high efficiency of 3.35%, identical to the device with PEDOT:PSS (3.35%). In addition, the PSC with UV–ozone treated ITO anode shows 3.6 times longer life-time than that with PEDOT:PSS.