Excimer emission in electroluminescence and photoluminescence of polyfluorene derivatives: Effects of local heating and exciton density

Abstract

We report a study of excimer emission from copolymers of dibutylfluorene and butylphenylphenoxazine. Temperature dependence of photoluminescence (PL) spectra measured from room temperature to above glass transition temperature, and excitation power dependence of PL spectra reveal that the observed differences in excimer intensity between PL and electroluminescence spectra are neither solely due to local heating by electric current nor to differences in exciton density. Instead, different nature of the excitations upon photoexcitation and excitation by passing current has to be considered to explain the different behavior.

On the origin of excimer emission in electroluminescence and photoluminescence spectra of polyfluorenes

“…We have measured a concentration dependence of the solution absorption spectra and verified that the red-shifted emission is not due to ground-state complexes. A possibility that the redshifted features are due to chemical degradation can also be ruled out [5] and it can be safely concluded that these features are due to excimer emission from the polymer film. Fig.…”

“…Explanations offered so far include local heating of the film by passing current, different density of excitons or different nature of the excitations. We have recently addressed these questions and found that neither local heating nor differences in exciton density can be responsible for the spectral differences observed [5]. In this paper, we compare these effects with the dependence of the excimer band on the device driving voltage and discuss the results in terms of the character of respective excitations.…”

Thin films of poly[(9,9-dioctylfluorene)-co-thiophene] deposited on ITO by the Langmuir–Schaefer and Langmuir–Blodgett techniques

“…The formation of aggregates originated by inter-chain interactions occurs typically in concentrated solid state systems and impairs the photo-and electroluminescence of the conjugated polymers by enhancing the non-radiative deactivation processes of the polymer chain. When the formation of these structures occurs, the absorption and emission spectra are shifted to the lower-energy red region [14][15][16].…”

The Effect of Controlled Dopant Concentration on the Performance of Blue Polymer Light‐emitting Diodes

“…As the NPB concentration increased to 3% NPB, molecular disorder became dominant and carrier mobility decreased. Researchers [25][26][27] have shown the appearance of a shoulder on the main emission peak results mainly from an enhanced molecular order structure that is induced by molecular aggregation of the emitting polymers such as BP105. As the concentration of NPB in BP105 was increased, as shown in Fig.…”