Device Performance Correlated with Structural Properties of Vertically Aligned Nanorod Arrays in Polymer/ZnO Solar Cells

Polymer-based solar cells consisting of ZnO nanorods and poly(1-methoxy-4-(2-ethylhexyloxy)-p-phenyl-enevinylene) (MEH-PPV) are investigated by current-voltage characterization and intensity modulated photovoltage spectroscopy (IMVS). The high quality ZnO nanorod arrays were prepared by electrodeposition, in which the length (L-n) and the concentration of deep level defects of ZnO nanorods were controlled by deposition time (T-d). Results show that increasing T-d leads to ZnO nanorods with linearly increased L-n but differently increased defect concentration for the MEH-PPV/ZnO solar cells, providing a peak device power conversion efficiency of 0.34% at AM 1.5 illumination (100 mW/cm(2)) for T-d = 10 min. The electron lifetimes in MEH-PPV/ZnO nanorod devices at open circuit were studied by means of IMVS for the first time, and the influences of L-n and defect concentration on the charge recombination kinetics and device performance were revealed. It is found that, in the MEH-PPV/ZnO devices with high quality ZnO nanorods with rather low defect concentration, both photocurrent and recombination rate are mainly dependent on the L-n value as a result of the exponential attenuation of incident light intensity in the device, but the open circuit voltage V-oc is more sensitive to the defect concentration. The present study provides new insights into designing the nanostructures for the hybrid photovoltaic devices based on vertically aligned one-dimensional nanoarrays.