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.

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We investigate hybrid organic/inorganic films using different polymers and CdSe quantum dots (QD) and nanorods (NR) with hexanoic acid (HA)-treated hexadecylamine (HDA) or pyridine as the capping ligands. The volume ratios of the polymer:nanoparticle (NP) blends are studied by spectroscopic ellipsometry and transmission intensity data. Effective medium approximation based on the results of the pristine films is applied. With this routine, the polymer/NP volume ratio of the blend can be identified. In combination with the mass ratio of the components, the mass density of the NP including the inorganic crystalline core and the organic ligand layer is obtained. A geometrical model for QD and NR allows for the estimation of the ligand layer thickness. We find pyridine and HDA after HA treatment to be 0.9 and 0.6 nm on the QD surface, respectively. By contrast, the effective thickness of the organic ligand is 3.0 nm on the investigated NR. In both cases, the organic layer is thicker than a monolayer of the expected pyridine due to the presence of extant synthesis ligands as a result of incomplete ligand exchange. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: [75][76][77][78][79][80][81][82] 2012