Accumulation of electric-field-stabilized geminate polaron pairs in an organic semiconductor to attain high excitation density under low intensity pumping

N. C. Giebink, S. R. Forrest
2006 Applied Physics Letters  
The recombination dynamics of geminate polaron pair ͑PP͒ states are investigated by monitoring electric-field-induced delayed fluorescence in thin films consisting of the green laser dye, Coumarin-6 ͑C6͒ doped at 1 wt % into 4 , 4Ј-bis͑N-carbazolyl͒biphenyl. We find that the PP decay follows −m ͑with m ϳ 0.1͒, where is the time that the PPs are held in the field. This sublinear decay suggests the possibility for accumulation of PPs over time that can then be reconverted into excitons upon field
more » ... excitons upon field removal. We demonstrate the generation of short ͑ϳ50 ns full width at half maximum͒ bursts of C6 fluorescence with peak intensities Ͼ20 times the steady-state fluorescence intensity ͑corresponding to a C6 singlet exciton density N S Ͼ 4 ϫ 10 15 cm 3 ͒ when pumped continuously by a low intensity ͑Ͻ1 W/cm 2 ͒ laser in the presence of a pulsed electric field.
doi:10.1063/1.2385840 fatcat:u6kytmb3nnekflw2q3ngd5p4x4