Efficiency Enhanced Hybrid Solar Cells Using a Blend of Quantum Dots and Nanorods



The cell performance of organic-inorganic hybrid photovoltaic devices based on CdSe nanocrystals and the semiconducting polymer poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) is strongly dependent on the applied polymer-to-nanocrystal loading ratio and the annealing temperature. It is shown here that higher temperatures for the thermal annealing step have a beneficial impact on the nanocrystal phase by forming extended agglomerates necessary for electron percolation to enhance the short-circuit current. However, there is a concomitant reduction of the open-circuit voltage, which arises from energy-level alterations of the organic and the inorganic component. Based on quantum dots and PCPDTBT, we present an optimized organic–inorganic hybrid system utilizing an annealing temperature of 210 °C, which provides a maximum power conversion efficiency of 2.8%. Further improvement is obtained by blending nanocrystals of two different shapes to compose a favorable n-type network. The blend of spherical quantum dots and elongated nanorods results in a well-interconnected pathway for electrons within the p-type polmer matrix, yielding maximum efficiencies of 3.6% under simulated AM 1.5 illumination.