Effect of polymer processing on the performance of poly(3-hexylthiophene)/ ZnO nanorod photovoltaic devices

Effective infiltration of the polymer into the nanostructured oxide is critical for optimizing the performance of hybrid π-conjugated polymer/nanostructured metal oxide semiconductor photovoltaic devices. We investigated the effect of polymer processing parameters, solvent selection, and thermal annealing on poly(3-hexylthiophene) (P3HT)/ZnO nanorod photovoltaic devices and found that these play an important role in the degree of polymer infiltration and the subsequent device performance. We demonstrate that using dichlorobenzene as a solvent produced better performance devices than using chloroform. In addition, the infiltration of P3HT into the ZnO nanorod array has been improved through annealing and subsequent slow cooling. Time-resolved microwave conductivity studies reveal an increase in the photoconductivity of the composite devices with annealing, resulting from changes in both the polymer and ZnO. The device performance was shown to increase with enhanced infiltration, and the devices that had been slow cooled from melt at 225°C demonstrated a V _OC of 440 mV, a J _SC of 1.33 mA/cm ², a fill factor of 48%, and a power conversion efficiency of 0.28%. In contrast to previously published results on P3HT infiltrated into mesoporous TiO ₂ (Appl. Phys. Lett. 2003, 83, 3380), we found that the device performance improves with increasing amount of the polymer embedded in the ZnO arrays, through proper solvent selection and polymer processing.