Slower carriers limit charge generation in organic semiconductor light-harvesting systems.
Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron-hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers.
Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Martin
M
Stolterfoht
Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Ardalan
A
Armin
Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Safa
S
Shoaee
Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.|Centre for Engineered Quantum Systems, Centre for Quantum Computation and Communication Technology, School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia.
Ivan
I
Kassal
Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Paul
P
Burn
Centre for Organic Photonics &Electronics, School of Mathematics and Physics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
Paul
P
Meredith