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Comparison of amine and sulphide layer-by-layer synthetic route for preparing of the photovoltaic CdSe quantum dots thin-films

Quantum dots (QDs) are semiconducting nanoparticles interesting due to their size- dependent optoelectronic properties. Cadmium selenide QDs are generally used in photovoltaic applications due to their tuneable bandgap. Various physical and chemical methods can be used for QDs preparation but chemical routes are more advantageous due to facile QDs shape and size control. However, when preparing thin-films from colloidal QDs, obtaining satisfactory geometry arises as the main obstacle due to particle aggregation. The former can can be prevented by applying surface modification agent during the course of the synthesis. Here we compare two methods for surface modification of colloidal CdSe QDs in the course of the layer-by-layer (LbL) deposition of thin- films ; (i) by ligand exchange and (ii) by silanization. Also, the impact of the solution temperature was also considered. Firstly, the prepared precursor solutions were injected into the growth solution. Longer reaction time resulted in bigger CdSe QD with narrower bandgaps. Surface was modified by: (i) ligand exchange of trioctylphosphine (i) silanization with tetraethoxy silane. Then the thin-films of CdSe QDs were created by LbL with varying several solution temperatures and number of layers. The linking layers for silanized and exchanged ligands QDs were (3-aminopropyl)triethoxysilane and poly(diallyldimethylammonium chloride). Layers were connected via electrostatic assembly or through hydrogen bonding and condensation reactions. Colloidal QDs solutions and derived thin-films were examined using dedicated structural analysis and combination of spectroscopic, morphologic and microscopic techniques. The analyses confirmed successful silanization, i.e. interconnecting of the QDs into thin-films. Testing confirms that morphology, surface roughness, thin-film thickness and appropriate distribution of the QD domains remain due to careful ligand exchange in solution stage, pointing out in thermally stable films without aggregation-based defunctionalisation. [1] J. Li, J. Chen, Y. Shen, X. Peng, Nano Res., 11 (2018) 3991-4004 [2] K. Surana, P.K. Singh, H.W. Rhee, B. Bhattacharya, J. Ind. Eng. Chem., 6 (2014) 1-6 [3] B.K. Pong, B.L. Trout, J.Y. Lee, Langmuir, 24 (2008) 5270-5276 [4] X. Liu, J. Han, W. Wu, Q. Shi, W. Li, C. Li, Chem. Lett., 45 (2016) 10-12

quantum dots, CdSe, dip coating

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