Improvement of ITO-free inverted polymer-based solar cells by using colloidal zinc oxide nanocrystals as electron-selective buffer layer

Sebastian Wilken*, Dorothea Scheunemann, Verena Wilkens, Jürgen Parisi, Holger Borchert

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

27 Citations (Scopus)

Abstract

In this study, we report on the improvement of ITO-free inverted polymer/fullerene solar cells by introducing a zinc oxide (ZnO) layer between the active layer and the cathode. The ZnO layers are deposited from solution, using colloidal ZnO nanocrystals with a rodlike shape, which are obtained using a wet-chemical synthesis route at low temperature. The nanocrystals are widely characterized with respect to their structural, optical, and electronic properties. In particular, simulations of powder X-ray diffraction data based on Rietveld refinement are shown to be a suitable method to characterize the average crystallite shape and particle size. Cyclic voltammetry reveals that nanocrystalline ZnO is an appropriate choice as electron-selective buffer layer in organic solar cells based on a bulk heterojunction of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Using ITO-free inverted solar cells in substrate configuration with an opaque Cr/Al/Cr bottom electrode, we demonstrate that introducing a cathodic interlayer of ZnO nanocrystals leads to a notable enhancement in photovoltaic performance. The magnitude of the effect is found to depend on the solvents used to process the active layer. In case of absorber blends processed from o-dichlorobenzene, we show an almost threefold increase in efficiency from 0.8 to 2.2% at an active area of 1 cm2.
Original languageEnglish
Pages (from-to)2386-2394
JournalOrganic Electronics
Volume13
DOIs
Publication statusPublished - 30 Jul 2012
Externally publishedYes
MoE publication typeA1 Journal article-refereed

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