Extrinsic and intrinsic dc photoconductivity in a conjugated polymer

Abstract

Steady-state photoconduction was studied in typically 100-nm-thick films of a polyphenylenevinylene derivative with ether linkages in the backbone. Samples were prepared in sandwich configuration between indium tin oxide ͑ITO͒ and Al electrodes. Forward photocurrents measured upon irradiating through the positively biased ITO electrode decreased by typically three orders of magnitude when a 8-10-nm-thick silicon monoxide ͑SiO͒ layer had been deposited on top of the ITO to prevent photoinjection of positive charge carriers. Insertion of a SiO layer can thus be used as a tool to separate extrinsic from intrinsic sources of optical charge-carrier generation. Analysis of the dependences of extrinsic and intrinsic photocurrents on temperature, electric field, and photon energy indicate that they can be described in terms of Onsager's theory of geminate pair dissociation in either one or three dimensions.

Ultrafast photogeneration mechanisms of triplet states inpara-hexaphenyl

“…The reverse biasing of the LED ensures negligible injection from the electrodes, so that exciton-carrier interactions can be disregarded. 21 Figure 1͑b͒ shows a (⌬T) MF spectrum obtained for a delay of 20 ps and an applied reverse bias of 16 V. We observe a transient decrease of SE ͓negative (⌬T/T) MF signal͔ and PA 1 ͓positive (⌬T/T) MF signal͔ that can be explained by field-induced dissociation of the singlet exciton population, similar to the effect under steady-state condition. [22][23][24][25] We emphasize that the correlated decrease of SE and PA 1 is a further indication for the assignment of PA 1 to singlet exciton transitions, whereas both PA 2 and PA 3 are increased by the applied field ͓negative (⌬T/T) MF signal͔, indicating a corresponding increase of polaron and triplet population.…”

Temperature dependent characteristics of poly(3 hexylthiophene)-fullerene based heterojunction organic solar cells

“…The general scheme of the charge carrier generation processes in nondegenerate conjugated polymers ͑without acceptor͒ can been described as follows: The mobile charge carriers responsible for the photocurrent are produced as a result of the dissociation of primarily generated singlet excitons due to interchain interaction, presence of oxygen, [6][7][8] or impurities.…”

Photoconduction in Alq3

“…Exciton dissociation can either take place in the bulk or at the electrode interface. 3,4,13,14 If exciton dissociation occurs at the interface, then excitons generated within a diffusion length from the electrode semiconductor interface can diffuse to the electrode, dissociate into free carriers and give rise to PC. The efficiency of exciton dissociation is dependent on the electrode.…”

“…If exciton dissociation at the electrode is the only source of PC, then for asymmetric electrodes, the PC-Voltage characteristics would be asymmetric and strongly depend on the sign of the voltage bias. 14 On the other hand if the PC arises from a bulk process, then the PC density (J pc ) is expected to be given by,…”

“…l e typically is about 10nm for many polymers and for Alq 3 . 14,17 Hence only light absorbed in a distance l e will contribute to the PC and is independent of the sample thickness d, for d > l e . 14 The spectral response of the sample will be independent of the sample thickness and symbatic with the absorption.…”