02903nas a2200325   4500008004100000022001400041245010100055210006900156260000800225300001400233490000800247520183600255100001602091700002802107700002802135700001702163700002102180700002202201700002002223700002002243700001902263700001902282700003302301700003202334700002502366700001802391700001702409700002002426856013102446       2023                        eng d  a0002-786300aCovalent organic framework thin-film photodetectors from solution-processable porous nanospheres0 aCovalent organic framework thinfilm photodetectors from solution  cJAN  a1649-16590 v1453 a<p>
	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 x 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 x10-3 cm2 V-1 S-1) compared to other as synthesized films, indicating the best photoactive characteristics.</p>
1 aBag, Saikat1 aSasmal, Himadri, Sekhar1 aChaudhary, Sonu, Pratap1 aDey, Kaushik1 aBlaette, Dominic1 aGuntermann, Roman1 aZhang, Yingying1 aPoloz, Miroslav1 aKuc, Agnieszka1 aShelke, Ankita1 aVijayaraghavan, Ratheesh, K.1 aAjithkumar, Thalasseril, G.1 aBhattacharyya, Sayan1 aHeine, Thomas1 aBein, Thomas1 aBanerjee, Rahul  uhttps://library.ncl.res.in/content/covalent-organic-framework-thin-film-photodetectors-solution-processable-porous-nanospheres