TY - JOUR
T1 - Ideal diode equation for organic heterojunctions. II. the role of polaron pair recombination
AU - Giebink, N. C.
AU - Lassiter, B. E.
AU - Wiederrecht, G. P.
AU - Wasielewski, M. R.
AU - Forrest, S. R.
PY - 2010/10/4
Y1 - 2010/10/4
N2 - In paper I, we proposed that current transport in a donor-acceptor heterojunction (HJ) depends on the balance of polaron pair (PP) dissociation and recombination. Here, we directly investigate these processes in archetype planar copper phthalocyanine (CuPc)/C60 and boron subpthalocyanine chloride (SubPc)/C60 HJs. Using intensity-modulated photocurrent spectroscopy (IMPS) along with emission from interfacial Pc/ C60 exciplex states, we monitor the geminate PP density at the HJ as a function of bias and illumination intensity. We find that the SubPc/ C60 PP density is limited by the dynamics of dissociation, where it increases from short circuit, and peaks at open circuit. In contrast, that of CuPc/ C 60 is dominated by faster recombination kinetics and declines monotonically over the same voltage domain. We conclude that the PP recombination rate depends on electric field, and propose a simple expression that qualitatively explains the observed exciplex luminescence and IMPS behavior for these HJs. Our results provide insight into polaron pair recombination, which governs the current-voltage characteristics of organic heterojunctions in the dark and under illumination.
AB - In paper I, we proposed that current transport in a donor-acceptor heterojunction (HJ) depends on the balance of polaron pair (PP) dissociation and recombination. Here, we directly investigate these processes in archetype planar copper phthalocyanine (CuPc)/C60 and boron subpthalocyanine chloride (SubPc)/C60 HJs. Using intensity-modulated photocurrent spectroscopy (IMPS) along with emission from interfacial Pc/ C60 exciplex states, we monitor the geminate PP density at the HJ as a function of bias and illumination intensity. We find that the SubPc/ C60 PP density is limited by the dynamics of dissociation, where it increases from short circuit, and peaks at open circuit. In contrast, that of CuPc/ C 60 is dominated by faster recombination kinetics and declines monotonically over the same voltage domain. We conclude that the PP recombination rate depends on electric field, and propose a simple expression that qualitatively explains the observed exciplex luminescence and IMPS behavior for these HJs. Our results provide insight into polaron pair recombination, which governs the current-voltage characteristics of organic heterojunctions in the dark and under illumination.
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U2 - 10.1103/PhysRevB.82.155306
DO - 10.1103/PhysRevB.82.155306
M3 - Article
AN - SCOPUS:78149233632
SN - 1098-0121
VL - 82
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 15
M1 - 155306
ER -