Attila J. Mozer

Charge transport and recombination in bulk heterojunction solar cells studied by the photoinduced charge extraction in linearly increasing voltage technique

Charge carrier mobility and recombination in a bulk heterojunction solar cell based on the mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-phenylene vinylene] (MDMO-PPV) and 1-(3-methoxycarbonyl)propyl-1-phenyl-(6,6)-C61 (PCBM) has been studied using the novel technique of photoinduced charge carrier extraction in a linearly increasing voltage (Photo-CELIV). In this technique, charge carriers are photogenerated by a short laser flash, and extracted under a reverse bias voltage ramp after an adjustable delay time (tdel). The Photo-CELIV mobility at room temperature is found to be μ=2×10−4cm2V−1s−1, which is almost independent on charge carrier density, but slightly dependent on tdel. Furthermore, determination of charge carrier lifetime and demonstration of an electric field dependent mobility is presented.

Double injection as a technique to study charge carrier transport and recombination in bulk-heterojunction solar cells

Ambipolar charge carrier mobility and recombination in bulk-heterojunction solar cells based on the mixture of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene (PCBM) has been studied using injection current transients. The experimental results demonstrate double injection with bimolecular recombination limiting the injection current. We found that charge carrier bimolecular recombination is significantly reduced compared to Langevin recombination. We have measured the temperature and electric field dependence of the reduced bimolecular recombination coefficient and the results suggest that the electron and hole pathways are different and the recombination is controlled by the probability of the carriers to meet at the polymer/PCBM interface.

Charge carrier transport and recombination in bulk-heterojunction solar-cells

We have measured charge carrier transport and recombination in bulk-heterojunction solar-cells. Time-of-flight, carrier extraction by linearly increasing voltage and double injection techniques which are complementary to each other have been used to study the solar-cells of different thicknesses and conductivities. We show the importance of carrier mobility and bimolecular recombination coefficient for testing the suitability of materials in bulk-heterojunction solar-cells. The reduced bimolecular recombination coefficient at zero electric field and its electric field dependence are measured directly. The bimolecular recombination coefficient and Langevin-type coefficient values β/βL ≈ 10-4 are in the good agreement when measured with presented techniques.