HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 86
B40 - Recombination in Organic Bulk Heterojunction Solar Cells: A Study of Interfacial
Charge Transfer Kinetics with Fullerene Affinity
Antonio Guerrero, Juan Bisquert, Germà Garcia-Belmonte
Universidad Jaume I, Avda. Sos Baynat, s/n Universidad Jaume I , Castellón, 12071, ES
One of the current strategies to improve power conversion efficiencies (PCE) of solutionprocessed
organic solar cells is looking at increasing the open circuit potential (Voc). By
increasing the energy offset between the donor highest occupied molecular orbital (HOMO)
and acceptor lowest unoccupied molecular orbital (LUMO) this can be achieved. Thus, one of
the followed approach is to replace [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) as
acceptor molecules by different fullerene derivatives with a lower electron affinity. 1
In this work a detailed analysis of the charge carrier recombination mechanism will be
presented for a series of three different fullerene derivatives. 2,3 The impedance technique
allows extracting parameters related to energetics as well as recombination kinetics
simultaneously. By using active layers of P3HT blended with fullerene acceptors of different
electron affinity, we demonstrate that the recombination coefficient is only slightly dependent
on the fullerene LUMO energy. Chemical capacitance values indicate that the distribution of
excess carriers within bandgap density-of states is very similar for all three.
Moreover the energy location of recombining carriers within the DOS has also a minor
influence on the recombination coefficient value. It is proposed that charge transfer events
accounting for the recombination process take place in the vicinity of the maximum rate in the
framework of the Marcus theory, with large reorganization energy values.
References
[1] He, Y.; Chen, H.-Y.; Hou, J.; Li, Y., "Indene-C60 Bisadduct: a New Acceptor for High-Performance Polymer Solar
Cells". J. Am. Chem. Soc., 132, 1377-1382 (2010).
[2] Bisquert, J.; Garcia-Belmonte, G., "On Voltage, Photovoltage, and Photocurrent in Bulk Heterojunction Organic
Solar Cells". J. Phys. Chem. Let., 2, (15), 1950-1964 (2011).
[3] Boix, P. P.; Guerrero, A.; Marchesi, L. F.; Garcia-Belmonte, G.; Bisquert, J., C"urrent-Voltage Characteristics of
Bulk Heterojunction Organic Solar Cells: Connection Between Light and Dark Curves". Adv. Energy Mat. 1, (6), 1073-
1078 (2011).
© SEFIN 2012