Improvement of Charge Collection and Performance Reproducibility in Inverted Organic Solar Cells by Suppression of ZnO Subgap States

Bo Wu, Zhenghui Wu, Qingyi Yang, Fu Rong ZHU*, Tsz Wai Ng, Chun Sing Lee, Sin Hang CHEUNG, Shu Kong SO

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)

Abstract

Organic solar cells (OSCs) with inverted structure usually exhibit higher power conversion efficiency (PCE) and are more stable than corresponding devices with regular configuration. Indium tin oxide (ITO) surface is often modified with solution-processed low work function metal oxides, such as ZnO, serving as the transparent cathode. However, the defect-induced subgap states in the ZnO interlayer hamper the efficient charge collection and the performance reproducibility of the OSCs. In this work, we demonstrate that suppression of the ZnO subgap states by modification of its surface with an ultrathin Al layer significantly improves the charge extraction and performance reproducibility, achieving PCE of 8.0%, which is ∼15% higher than that of a structurally identical control cell made with a pristine ZnO interlayer. Light intensity-dependent current density-voltage characteristic, photothermal deflection spectroscopy, and X-ray photoelectron spectroscopy measurements point out the enhancement of charge collection efficiency at the organic/cathode interface, due to the suppression of the subgap states in the ZnO interlayer.

Original languageEnglish
Pages (from-to)14717-14724
Number of pages8
JournalACS applied materials & interfaces
Volume8
Issue number23
DOIs
Publication statusPublished - 15 Jun 2016

Scopus Subject Areas

  • Materials Science(all)

User-Defined Keywords

  • charge collection
  • organic solar cells
  • organic/cathode interface
  • oxide interlayer
  • subgap states

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