Publication date: 1st April 2013
A tremendous effort is spent in findings ways to improve upon the efficiency and cost of photovoltaics. Quantum dot sensitized solar cells (QDSSCs) are cheap, flexible and reliable devices that are expected to play a major role in future solar technologies. We believe that theoretical modeling can greatly aid the development of this emerging technology by accurate simulation of the complex hetero-composite interfaces that determine the performance of these solar devices.
In this project, we test the reliability of our computational approach on a realistic system currently used in QDSSC technology, namely the inorganic/organic hybrid nanocomposite materials of a quantum dot attached to carbon nanomaterials, like C60. Our work has been inspired by the experiments carried out in the Kamat group[1]. Here, we exploit our computational resources to provide details on the parameters at the base of the Marcus theory of electron transfer that governs the processes of charge separation and charge recombination: electron coupling, reorganization energy and free Gibbs energy driving force. Important differences are found on simulated electron transfer rates when a small CdSe quantum dot is directly attached to C60 via a thiol functionalized ligand versus the same QD weakly coupled to C60 (Figure 1). In particular, larger electron couplings and driving forces are at the origin of the faster photoinduced transfer on the thiol functionalized QD.
These calculations have been carried out by a cutting-edge combination of theoretical methods encompassing molecular dynamics and density functional theory (DFT).
Our long-term vision is to design a versatile computational tool to select “in-silico” the best modifications of the hetero-composite interfaces of a CdSe quantum dot chemically attached to inorganic or organic semiconductors, in order to optimize the cell operation. This tool will be developed as an efficient computational protocol that can be used together with experiments in the construction of better QDSSC.
Figure 1 : Structure of a (CdSe)33 quantum dot attached to a C60 fullerene (left) and thiol functionalized C60 fullerene. Geometries are optimized with DFT.
[1] Bang, J. H.; Kamat, P. V. CdSe Quantum Dot–Fullerene Hybrid Nanocomposite for Solar Energy Conversion: Electron Transfer and Photoelectrochemistry, ACS Nano, 2011, 5 (12), pp 9421–9427
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