Photostimulated currents and magnetic spin effects in organic p-n polymeric heterostructures
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Generation of charged current carriers in photovoltaic cells with polymeric p-n heterostructures as an active layer was studied. Photo- and thermofield stimulation of Pool-Frenkel type states at the p-n interface of polymeric heterostructures based on p (doped polyimides) and n type (doped carbazolyl-containing polymers and polyesteramides) was found to cause the generation of current carriers and observation of photostimulated currents. These states are interpreted as stabilized pairs of charges consisting of carriers captured by deep charged centers with the opposite sign. They are presumably formed at the interface as a result of an irreversible photochemical reaction of the free radical type of a radical-ion pair, which appears in the phototransfer of an electron from a donor polyimide fragment to an excited dopant particle. The effectiveness of the formation and accumulation of these states was found to increase as the surface area and the degree of interface development (sharp, diffuse, volume) grew. Photostimulated currents were shown to influence the photovoltaic characteristics of cells based on polymeric p-n heterostructures: an increase in short circuit photocurrent (by more than an order of magnitude for a volume interface and by several times for a diffusion interface) was observed, and free running voltage increased (to 1.2–1.4 V). This allows the energy effectiveness of photovoltaic cells to be substantially increased at a moderate increase in temperature (by no more than 20–30°C), in particular, because of nonactinic light source IR radiation. The formation of ion-radical pairs and their relation to Pool-Frenkel states is substantiated by observed positive magnetic field influence (H < 1 kOe, T = 293−323 K) on the yield of luminescence of dopant particles and photostimulated current (magnetic spin effects by the hyperfine interaction mechanism).
Keywordsp-n type heterostructures photostimulated currents magnetic effect
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