Interfacial engineering of electron transport layer using Caesium Iodide for efficient and stable organic solar cells

Mushfika Baishakhi Upama, Naveen Kumar Elumalai, Md Arafat Mahmud, Matthew Wright, Dian Wang, Cheng Xu, Faiazul Haque, Kah Howe Chan, Ashraf Uddin

Research output: Contribution to journalArticlepeer-review


Polymer solar cells (PSCs) have gained immense research interest in the recent years predominantly due to low-cost, solution process-ability, and facile device fabrication. However, achieving high stability without compromising the power conversion efficiency (PCE) serves to be an important trade-off for commercialization. In line with this, we demonstrate the significance of incorporating a CsI/ZnO bilayer as electron transport layer (ETL) in the bulk heterojunction PSCs employing low band gap polymer (PTB7) and fullerene (PC71BM) as the photo-active layer. The devices with CsI/ZnO interlayer exhibited substantial enhancement of 800% and 12% in PCE when compared to the devices with pristine CsI and pristine ZnO as ETL, respectively. Furthermore, the UV and UV-ozone induced degradation studies revealed that the devices incorporating CsI/ZnO bilayer possess excellent decomposition stability (∼23% higher) over the devices with pristine ZnO counterparts. The incorporation of CsI between ITO and ZnO was found to favorably modify the energy-level alignment at the interface, contributing to the charge collection efficiency as well as protecting the adjacent light absorbing polymer layers from degradation. The mechanism behind the improvement in PCE and stability is analyzed using the electrochemical impedance spectroscopy and dark I–V characteristics.
Original languageEnglish
Pages (from-to)834-844
Number of pages11
JournalApplied Surface Science
Publication statusPublished - 2017
Externally publishedYes


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