The Effect of Organic and Metal Oxide Interfacial layers on the Performance of Inverted Organic Photovoltaics

Abstract

Abstract We study the origin of the improvement of the power conversion efficiency (PCE) of inverted organic solar cells when an interfacial insulating organic layer of polyoxyethylene tridecyl ether (PTE) is introduced between the indium tin oxide (ITO) bottom electrode and the TiO x interfacial layer. XPS and UPS measurements are used to investigate the energy level alignment at the interfaces within the ITO/TiO x and ITO/PTE/TiO x structures and to identify any effects due to chemical interaction and interfacial dipoles. Scanning electron microscopy studies show that the surface structure of the TiO x layer is affected, when it is coated on top of the PTE layer. Surface contact angle measurements show that the incorporated interfacial layer of PTE is more hydrophilic than ITO and thus PTE modified TiO x becomes more hydrophilic. This, in combination with the surface gaps of the PTE interfacial layer, is likely to lead to changed wetting and hydrolysis properties of TiO x when coated on ITO/PTE than on ITO alone. The different TiO x layer quality is reflected in improved electron selectivity, leading to enhanced fill factor, reduced parasitic resistance effects and higher power conversion efficiency for inverted solar cells with a PTE interfacial layer between ITO and TiO x .