Kinetic Monte Carlo Simulations of Charge Recombination in Organic Photovoltaics
Chris Groves
School of Engineering and Computing Sciences, Durham University, UK
http://community.dur.ac.uk/chris.groves/
17:15 - 18:15 Tuesday 01 July 2014 TUG P2 Although Organic Photovoltaic devices (OPVs) suffer from a variety of properties that might be expected to impact device performance, including high recombination rate and small dielectric constants, real devices nonetheless show charge generation efficiencies approaching 100%. In this talk I will discuss recent work in my group in which kinetic Monte Carlo (KMC) simulations have been used to try and understand this apparent discrepancy. Two broad areas will be considered, the morphology of the OPV and energetic structure at the interface.
We will show that counter to expectation, it is the morphology in the region of the donor-acceptor heterojunction which most affects the device performance rather than longer range features (i.e. domain sizes). Further, we show that surface morphology, and in particular unfavourable wetting layers, have relatively little impact on OPV performance due to their small thickness. We also consider energetic structure at the interface. Some of our recent work has focussed on hot charge transfer states in polymer-fullerene OPVs. In this we quantify the impact of an initially delocalised electron wavefunction immediately after charge separation. Interestingly we find that delocalisation has relatively little impact, at least over the reported ranges of delocalisation in the literature. This is explained in terms of a balance between kinetics and energetics of charge separation. Conversely, heterojunction cascades, as may occur in P3HT:PCBM solar cells, are shown to have a significant benefit to charge separation.
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