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

Research output: Contribution to journalArticlepeer-review

7 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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