Unraveling Urbach Tail Effects in High-Performance Organic Photovoltaics: Dynamic vs Static Disorder

Chujun Zhang, Sudhi Mahadevan, Jun Yuan, Johnny Ka Wai Ho, Yaxin Gao, Wei Liu, Hui Zhong, He Yan, Yingping Zou, Sai Wing Tsang, Shu Kong So*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

50 Citations (Scopus)


The origin of Urbach energy (EU) in organic semiconductors and its effect on photovoltaic properties remain a topic of intense interest. In this letter, we demonstrate quantitative information on the EU value in emerging Y-series molecules by an in-depth analysis of the line shape of the temperature-dependent quantum efficiency spectra. We found that the static disorder (EU(0)), which is dominated by the conformational uniformity in Y-series acceptors, contributes 10–25 meV to the total Urbach energy. Particularly, this static contribution in organic solar cells (OSCs) is much higher than those (EU(0) ≈ 3–6 meV) in inorganic/hybrid counterparts, such as CH3NH3PbI3 perovskite, crystalline silicon (c-Si), gallium nitride (GaN), indium phosphide (InP), and gallium arsenide (GaAs). More importantly, we establish clear correlations between the static disorder and photovoltaic performance and open-circuit voltage loss. These results suggest that suppressing the static disorder via rational molecular design is clearly a path for achieving higher performance.
Original languageEnglish
Pages (from-to)1971–1979
Number of pages9
JournalACS Energy Letters
Issue number6
Early online date16 May 2022
Publication statusPublished - 10 Jun 2022

Scopus Subject Areas

  • Chemistry (miscellaneous)
  • Energy Engineering and Power Technology
  • Materials Chemistry
  • Fuel Technology
  • Renewable Energy, Sustainability and the Environment


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