Chin. Phys., 2005, Vol. 14(12): 2590-2594    DOI: 10.1088/1009-1963/14/12/034
 CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES Prev   Next

Energy transfer probability in organic electrophosphorescence device with dopant

Dai Guo-Zhang, Li Hong-Jian, Pan Yan-Zhi, Dai Xiao-Yu, Xie Qiang
Department of Applied Physics, Hunan University, Changsha 410082, China
Abstract  Based on the energy transfer process from host to dopant in an organic electrophosphorescent (EP) device, the expression of energy transfer probability ($\eta )$ between the host (TPD) and guest (Ir(ppy)$_{3})$ EP systems was proposed. The results show that: ({1}) The rate of the triplet energy transfer ($K_{\rm HG}$ and $K_{\rm GH})$ increases exponentially with increasing donor-acceptor molecular distance ($R$), whereas decreases as the intermolecular distance ($R_{\rm HH})$ increases from 0.8 to 2.4 nm. Furthermore, $K_{\rm GH}$ changes more quickly than $K_{\rm HG.}$ ({2}) The energy transfer probability ($\eta )$ increases as $R$ reduces, and the $R_{\rm HH}$ changes can be safely neglected for $R<$0.9 nm. The situation changes for 0.9nm$< R < 1.1$nm, $R_{\rm HH }$ ($<1$nm) plays an essential role when $\eta$ changes and increases with the latter. However, if $R > 1.1$nm, the transfer probability will be below zero. Here, the energy transfer principle may be less important, and the high electroluminescence (EL) quantum efficiency of phosphorescent system will be attributed to the direct electron-hole recombination in phosphorescent molecules. ({3}) The $\eta$ will increase when the Forster radius ($R_{0})$ increases or Gibb's energy decreases.
Keywords:  electrophosphorescence      energy transfer      triplet
Received:  22 April 2005      Revised:  24 August 2005      Accepted manuscript online:
 PACS: 78.60.Fi (Electroluminescence)
Fund: Project supported by the Excellent Youth Foundation of Hu'nan Province (Grant No 03JJY1008), and by the Science Foundation for Post-doctorate of China (Grant No 2004035083).