Covalent Organic Framework Thin-Film Photodetectors from Solution-Processable Porous Nanospheres

Saikat Bag, Himadri Sekhar Sasmal, Sonu Pratap Chaudhary, Kaushik Dey, Dominic Blätte, Roman Guntermann, Yingying Zhang, Miroslav Položij, Agnieszka Kuc, Ankita Shelke, Ratheesh K. Vijayaraghavan, Thalasseril G. Ajithkumar, Sayan Bhattacharyya, Thomas Heine, Thomas Bein, Rahul Banerjee

Research output: Contribution to journalArticlepeer-review


The synthesis of homogeneous covalent organic framework (COF) thin films on a desired substrate with decent crystallinity, porosity, and uniform thickness has great potential for optoelectronic applications. We have used a solution-processable sphere transmutation process to synthesize 300 ± 20 nm uniform COF thin films on a 2 × 2 cm2 TiO2-coated fluorine-doped tin oxide (FTO) surface. This process controls the nucleation of COF crystallites and molecular morphology that helps the nanospheres to arrange periodically to form homogeneous COF thin films. We have synthesized four COF thin films (TpDPP, TpEtBt, TpTab, and TpTta) with different functional backbones. In a close agreement between the experiment and density functional theory, the TpEtBr COF film showed the lowest optical band gap (2.26 eV) and highest excited-state lifetime (8.52 ns) among all four COF films. Hence, the TpEtBr COF film can participate in efficient charge generation and separation. We constructed optoelectronic devices having a glass/FTO/TiO2/COF-film/Au architecture, which serves as a model system to study the optoelectronic charge transport properties of COF thin films under dark and illuminated conditions. Visible light with a calibrated intensity of 100 mW cm-2 was used for the excitation of COF thin films. All of the COF thin films exhibit significant photocurrent after illumination with visible light in comparison to the dark. Hence, all of the COF films behave as good photoactive substrates with minimal pinhole defects. The fabricated out-of-plane photodetector device based on the TpEtBr COF thin film exhibits high photocurrent density (2.65 ± 0.24 mA cm-2 at 0.5 V) and hole mobility (8.15 ± 0.64 ×10-3 cm2 V-1 S-1) compared to other as-synthesized films, indicating the best photoactive characteristics.

Original languageEnglish
Pages (from-to)1649-1659
Number of pages11
JournalJournal of the American Chemical Society
Issue number3
Publication statusPublished - 2023 Jan 25

Bibliographical note

Funding Information:
S.B. and S.P.C. acknowledge CSIR for a Research Fellowship. H.S.S. acknowledges DST-SERB, India, for an RA Fellowship [CRG/2018/000314]. K.D. acknowledges DST-SERB, India, for an RA Fellowship [CRG/2018/000314]. R.B. acknowledges the SwarnaJayanti Fellowship grant [DST/SJF/CSA-02/2016-2017], DST Mission Innovation [DST/TM/EWO/MI/CCUS/17 and DST/TMD(EWO)/IC5-2018/01(C)], and DST-SERB [CRG/2018/000314] for funding. R.B. and T.B. also acknowledge the Carl Friedrich von Siemens Research Fellowship and the Alexander von Humboldt Foundation for a research stay at Ludwig-Maximilians Universität (LMU) in München, Germany. S.Bh. thanks SERB for funding under Sanction No. CRG/2020/000084 and STR/2021/000001. T.B. acknowledges support from the Center for NanoScience Munich (CeNS) and the Bavarian research network Solar Technologies go Hybrid (SolTech) as well as funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany′s Excellence Strategy─EXC 2089/1─390776260. Y.Z. acknowledges the China Scholarship Council. M.P. acknowledges the Saxonian Ministry for Science and Art (DCC F-012177-701-XD0-1030602) for funding. Y.Z., M.P., A.K., and T.H. acknowledge ZIH Dresden for computer time. Y.Z., A.K., and T.H. acknowledge Deutsche Forschungsgemeinschaft for support within CRC 1415 and SPP2244. We acknowledge R.B. Amal Raj and E. Bhoje Gowd for helping in PXRD data collection.

Publisher Copyright:
© 2023 American Chemical Society.

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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