Photovoltaic performance of the hybrid devices consisting of polymer/fullerene/ZnO nanorod array was studied. The dependence of the photovoltaic performance on the ZnO nanorod length and the organic layer thickness was investigated, and it is concluded that the ZnO nanorod array plays an important role in collecting photogenerated electrons and acts as a conducting path to the indium tin oxide electrode. Fill factor of the devices increased from 38% to 50% when the array of the ZnO nanorods was introduced, which directly contributed to the improvement of the power conversion efficiencies up to 2.7%. As the peak absorption of the device reaches >97% in a transmitting geometry, the results shown here give us insights toward designing the devices with efficient utilization of the incident light.

We designed and synthesized the all-conjugated diblock copolymers poly(3-hexylthiophene-block-3-(2-ethylhexyl)thiophene)s (P(3HT-b-3EHT)s) via a modified Grignard metathesis (GRIM), a type of quasi-living polymerization, and studied their microphase-separated structures. The P(3HT-b-3EHT)s synthesized had well-controlled molecular weights and very narrow polydispersity indices (PDIs), which demonstrates the usefulness of GRIM polymerization for the synthesis of semiconducting block copolymers. P(3HT-b-3EHT)s self-organized to form clear microphase-separated patterns upon thermal treatment, as observed by AFM. Interestingly, the enhancement of the interchain interaction of the P3HT segments compared with the P3HT homopolymer was clearly observed from the UV-vis spectra, despite the fact that the amount of crystalline P3HT fraction was reduced to 83% of the total polymer amount in P(3HT-b-3EHT). It is suggested that the relatively unconstrained, amorphous segments of P3EHT can enhance the crystallization of P3HT segments to form an ordered self-organized nanostructure.

We have developed a new method to fabricate an array of TiO2 nanorod assemblies on a flat TiO2 surface. The TiO2 nanostructures with a height of approximately 40 nm were synthesized via a low temperature sol−gel reaction in a reversed micelle system. Cross-sectional transmission electron microscopy observation revealed that each nanostructure is an assembly of nanorods with a diameter and length of approximately 4 nm and approximately 40 nm, respectively. The fabricated array of TiO2 nanorods was applied to construct photovoltaic devices combined with a semiconducting polymer. When the nanostructured TiO2 substrate is used, photovoltaic performance reaches a power conversion efficiency of 0.39% and a fill factor of 0.47 under AM 1.5 illumination. Dependence of external quantum efficiency on polymer thickness showed the maximum efficiency in a thicker polymer film condition in the presence of the TiO2 nanorod assembly, indicating the nanostructure functions as an efficient exciton collector.