Spatial Homogeneity and Environmental Degradation Affected by Hole Transport Layers in Organic Solar Cells
Huei-Ting Chien
Institute of Solid State Physics
12:40 - 13:20 Friday 19 January 2018 PH01150

Organic photovoltaic cells (OPV) have received considerable attention as potential source of renewable energy for their advantages as easy fabrication, light weight, low manufacturing cost and mechanical flexibility. The improvement of device efficiency due to incorporation of a hole-transport layer (HTL) in bulk-heterojunction solar cells has been extensively reported. However, the most widely used HTL material, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is frequently suspected to be the dominating source for device’s instability under environmental conditions for its hygroscopic and acidic nature. And its colloidal nature is suspected to be responsible for spatial inhomogeneities and irreproducibility. Transition metal oxide (TMO) semiconductors are considered attractive alternative materials for the replacement of PEDOT:PSS. In this study, two different solution processed molybdenum trioxide (MoO3), obtained from two liquid precursors, incorporated as the HTL in OPV are demonstrated, one is quasi-continuous MoO3 with alcohol-based precursor solution and the other is a colloidal MoO3 with water-based precursor solution.
Initially, a combined comparison of different imaging techniques between different HTL materials and bare indium tin oxide (ITO) electrode is performed to discuss the layers’ properties from nano- to macroscale and demonstrate their impact upon implementation into OPV devices, via spatially-resolved characterization. Furthermore, different degradation mechanisms of solar cell are discussed by exposing different HTLs to various environments such as oxygen, light or humidity, prior to device finalization under inert conditions. This allows investigating any effects within the HTL and from reactions at its interface to the ITO electrode or the active layer. Finally, the induced degradation and spatial inhomogeneity of OPV devices under different environmental conditions, uncoupled from the influence of any auxiliary HTL are studied. This enables to observe degradation mechanisms without the influence of HTL material.