Carrier Generation Process in Poly(p-phenylene vinylene) by Fluorescent Quenching and Delayed-Collection-Field Techniques

Abstract

The carrier generation process in poly(p-phenylene vinylene) (PPV) has been investigated by using fieldinduced fluorescent quenching and delayed-collection-field techniques under pulsed illumination. Relative photoresponse and fluorescent quenching have been measured at electric fields of up to 300 V/µm. The results demonstrate a linear relation between fluorescent quenching and photoresponse at high electric fields, indicating that almost all field-quenched excited states lead to carrier generation. Experimental results also indicate that the time decay of e-h pairs is highly dispersive and the majority (70%) of them decay nonexponentially to ground state in ∼1 ms after illumination. Fluorescent quenching and carrier generation efficiencies obtained at the highest applied electric field are 34% and 42%, respectively. Results also suggest that carrier generation in PPV is a two-step process. In the first step, excited singlet states dissociate into bound geminate e-h pairs, and in the second step, the geminate pairs are separated into free carriers. Both steps are influenced by the applied electric field.

Electric-field-induced singlet and triplet exciton quenching in films of the conjugated polymer polyspirobifluorene

“…Usually, studies on the electricfield-induced quenching of the photoluminescence of conjugated polymers yielded a maximum quenching of 30 to 40%. 3,4,8,11,12,14,25,26 For MeLPPP, Tasch et al report a fieldinduced quenching of 76%, but the samples used exhibit strong signs of keto defects. 27 Unlike the commonly used pulsed laser sources, these authors employed a Xe lamp as the continuous excitation source.…”

“…Here it is generally assumed that the dissociation process of a singlet exciton into free charge carriers is a sequential process, which initially leads to the formation of a metastable Coulombically bound pair of charge carriers. [8][9][10][11] This assumption is mainly based on luminescence studies under applied electric fields using MeLPPP, where a spike in the delayed fluorescence intensity accompanies the switchoff of a strong electric field in the microsecond time domain after pulsed excitation. 12 This observation was interpreted in terms of field-stabilized geminate pairs, which, again, collapse into singlet excitons once the external field is turned off.…”

Electric-field effects on photoinduced dynamics and function

“…The fieldinduced quenching observed at rather weak fields, which is more efficient at shorter wavelength excitation, may be ascribed to the field-induced enhancement of the electron transfer, which occurs from highly excited state through the π-conjugated polymer chain [27]. Similar electric-field effects on PL intensity and decay were observed in other π-conjugated polymers such as PPV derivatives [29,30]. It is noted that the field-assisted dissociation of the photoexcited state, which leads to the fieldinduced quenching of PL, also occurs in semiconductor quantum dots such as CdS or CdTe nanoparticles [31,32].…”

“…It is noted that ITMT occurs with photoirradiation with applied voltages larger than the threshold value [33]. Photoirradiated crystals show differential negative resistance [30], and bistability (i.e., hysteresis loop) was observed in the I-V characteristic curve, as shown in Fig. 6c, which shows the plots obtained by scanning the pulsed voltage height in the positive and negative directions with photoirradiation at the same intensity.…”

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

“…Since the discovery, variables such as setting time, temperature, amount of conjugation of the polymer, addition of an electron transport layer, electrode material selection, and the introduction of disorder into the polymer have been optimized to develop a gain layer with efficiencies around 2% of photons emitted per injected electron [125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142] .…”