title: High-efficiency inverted polymer solar cells controlled by the thickness of polyethylenimine ethoxylated (PEIE) interfacial layers.
abstract: In this work, we investigate the effect of the thickness of the polyethylenimine ethoxylated (PEIE) interface layer on the performance of two types of polymer solar cells based on inverted poly(3-hexylthiophene) (P3HT):phenyl C61-butryric acid methyl ester (PCBM) and thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Maximum power conversion efficiencies of 4.18% and 7.40% were achieved at a 5.02 nm thick PEIE interface layer, for the above-mentioned solar cell types, respectively. The optimized PEIE layer provides a strong enough dipole for the best charge collection while maintaining charge tunneling ability. Optical transmittance and atomic force microscopy measurements indicate that all PEIE films have the same high transmittance and smooth surface morphology, ruling out the influence of the PEIE layer on these two parameters. The measured external quantum efficiencies for the devices with thick PEIE layers are quite similar to those of the optimized devices, indicating the poor charge collection ability of thick PEIE layers. The relatively low performance of devices with a PEIE layer of thickness less than 5 nm is the result of a weak dipole and partial coverage of the PEIE layer on ITO.
authors.affiliation: Institute for Clean Energy and Advanced Materials, Faculty of Materials and Energy, Southwest University, Chongqing 400715, P. R. China. qunliang@gmail.com qlsong@swu.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.forename: Gang
authors.initials: G
authors.lastname: Wang
authors.forename: Lun
authors.initials: L
authors.lastname: Cai
authors.forename: Baofu
authors.initials: B
authors.lastname: Ding
authors.forename: Dachen
authors.initials: D
authors.lastname: Zhou
authors.forename: Yi
authors.initials: Y
authors.lastname: Hu
authors.forename: Yujun
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jin
authors.initials: J
authors.lastname: Xiang
authors.forename: Keming
authors.initials: K
authors.lastname: Wan
authors.forename: Lijia
authors.initials: L
authors.lastname: Chen
authors.forename: Kamal
authors.initials: K
authors.lastname: Alameh
authors.forename: Qunliang
authors.initials: Q
authors.lastname: Song