Polaron pair mediated triplet generation in polymer/fullerene blends.
Electron spin is a key consideration for the function of organic semiconductors in light-emitting diodes and solar cells, as well as spintronic applications relying on organic magnetoresistance. A mechanism for triplet excited state generation in such systems is by recombination of electron-hole pairs. However, the exact charge recombination mechanism, whether geminate or nongeminate and whether it involves spin-state mixing is not well understood. In this work, the dynamics of free charge separation competing with recombination to polymer triplet states is studied in two closely related polymer-fullerene blends with differing polymer fluorination and photovoltaic performance. Using time-resolved laser spectroscopic techniques and quantum chemical calculations, we show that lower charge separation in the fluorinated system is associated with the formation of bound electron-hole pairs, which undergo spin-state mixing on the nanosecond timescale and subsequent geminate recombination to triplet excitons. We find that these bound electron-hole pairs can be dissociated by electric fields.
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Stoichko D
0000000215647080
SD
Dimitrov
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Scot
S
Wheeler
Department of Physics, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Dorota
D
Niedzialek
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Bob C
BC
Schroeder
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Hendrik
H
Utzat
Department of Physics, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Jarvist M
0000000319384430
JM
Frost
Department of Physics, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Jizhong
J
Yao
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Alexander
A
Gillett
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Pabitra S
PS
Tuladhar
1] Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK [2] SPERC, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia.
Iain
I
McCulloch
Department of Physics, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Jenny
J
Nelson
Department of Chemistry, Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
James R
JR
Durrant