Modification of PEDOT PSS films using ZnI2 additive for power conversion efficiency enhancement of organic solar cells

Abstract

Organic solar cells (OSCs) fabricated with poly(3 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) films often have limited performance due to high sheet resistances since commercial PEDOT:PSS contains a high insulating PSS to conducting PEDOT ratio. To resolve this issue zinc iodide (ZnI2) additive was utilized to modify PEDOT:PSS films which was carried out by mixing ZnI2 with PEDOT:PSS solution. The mixture was deposited on a fluorine-doped tin oxide substrate to derive the modified PEDOT:PSS films for application as a hole-transporting layer in OSCs. This resulted in an enhanced power conversion efficiency for OSCs fabricated with modified PEDOT:PSS films. The enhancement was primarily due to the improved PEDOT:PSS/PCDTBT:PC70BM (poly[N-9?-heptadecanyl-2 7-carbazole-alt-5 5-(4? 7?-di-2-thienyl-2? 1? 3?-benzothiadiazole)] � PCDTBT [6 6]-phenyl-C71-butyric acid methyl ester � PC70BM) interfaces which facilitates enhanced hole collection performance and results in a high current density for OSC devices. Moreover the ZnI2 plays a role in the depletion of insulating PSS from the film抯 surface. This behavior causes lower sheet resistance and results in an in-creased Jsc and Voc for OSC devices. Therefore the improved interfacial contact and depletion of PSS are considered syner-gistic functions for OSC enhancement. ? BME-PT.