HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 23
A8 - Understanding heterojunction solar cells through studies of the charge transfer
state
Jenny Nelson a , Mark Faist a , Thomas Kirchartz a , Sheridan Few a , James Kirkpatrick b
a, Imperial College London, Department of Physics, Blackett Laboratory, Prince, London, 0, UK
b, University of Oxford, Parks Road, Oxford OX1 3LB,UK, UK
Efficient current and voltage generation in organic and hybrid heterojunction devices
depends upon the driving forces for charge separation at the heterojunction and on the
energies of the states involved. In this work we use electroluminescence spectroscopy to
probe the energy of charge transfer (CT) states relative to the energies of excited states in the
donor and acceptor components and, together with device measurements, to study the
relationship between the CT state energy in and photocurrent generation efficiency. Through
study of a wide range of polymer:fullerene combinations we show that CT state emission is
positively correlated to photocurrent generation and that charge separation is switched off
when the CT state energy approaches the energy of the lowest singlet excited state of the
donor or acceptor.
The experimental results are rationalised through theoretical calculations of the CT states.
We extend the studies to other types of heterojunction and, finally, use our results to discuss
the factors that limit current and voltage generation in heterojunction solar cells.
References
[1] Faist MA, Kirchartz T, Gong W, et al, Competition between the Charge Transfer State and the Singlet States of
Donor or Acceptor Limiting the Efficiency in Polymer:Fullerene Solar Cells., J Am Chem Soc, 2012, Vol:134,
Pages:685-692
© SEFIN 2012