Solution-Processed Small Molecule Inverted Solar Cells: Impact of Electron Transport Layers

Abstract

In this work, the use of poly [(9,9-bis (30- (N,N-dimethylamino) propyl) -2,7-fluorene) -alt-2,7- (9,9-dioctylfluorene) (PFN) as electron transport layer (ETL) in inverted small molecule solar cells (SM-iOSCs) is analyzed. The optical and electrical characteristics obtained are compared with those obtained for similar SM-iOSCs where the ETL was zinc oxide. The p-DTS(FBTTh2)2 and PC70BM materials are used as donor and acceptor in the bulk heterojunction active layer, respectively for all devices. The photovoltaic devices exhibited a power conversion efficiency of 6.75% under 1 sun illumination. Impedance measurements were used to understand the causes that dominate the performance of the devices. We found that the loss resistance is governed by the PFN layer, which results in a lower fill factor value. Studies of atomic force microscopy, external quantum efficiency, and absorption UV-vis on the active layer have been performed to understand the effects of the charge transport dynamics on the performance of the devices.

Keywords

• Buffer layers
• dependence light intensity
• electron transport layer
• impedance spectroscopy
• organic solar cells
• p-DTS(FBTTh₂)₂:PC₇₀BM solar cells