Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics

Hao Wen Cheng, Putikam Raghunath, Kai Li Wang, Pei Cheng, Tianyi Haung, Quantan Wu, Jun Yuan, Yu Che Lin, Hao Cheng Wang, Yingping Zou, Zhao Kui Wang, Ming-Chang Lin, Kung-Hwa Wei*, Yang Yang*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach - treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide - to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Original languageEnglish
Pages (from-to)715-721
Number of pages7
JournalNano Letters
Issue number1
StatePublished - 8 Jan 2020


  • DFT calculation
  • nonfullerene acceptors
  • Organic photovoltaics
  • potassium
  • vertical phase separation


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