Hybrid Nanorod-Polymer Solar Cells
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We used between 5 and 15% pyridine in chloroform. The optimal amount of pyridine is determined by the number of nonpassivated Cd surface sites on the nanorods. An excess of pyridine however is to be avoided as this mediates the precipitation of P3HT which is insoluble in pyridine. Replacing chloroform with this solvent mixture leads to an increase in energy conversion efficiency of more than 50%.
The FF is defined as FF = {I·V}maxISC·VOC where I SC and V OC are short circuit current and open circuit voltage respectively. The power conversion efficiency is η = FF·ISC·VOClight intensity. The power conversion efficiency can be calculated both under monochromatic and white light (such as solar) illumination.
The sun simulator essentially consists of a 75 W xenon source and a set of Oriel A.M. 0 and A.M. 1.5 filters (Stratford CT). The temperature was maintained at 25°C verified by an in situ thermocouple by flowing argon past the device during measurements. The spectral overlap and intensity integral between the A.M. 1.5 Global standard (with spectral standard ASTM E892 Global and intensity of 96.4 mW/cm 2 ) and our sun simulator were optimized for the wavelength region in which the active layer shows absorption. The error in the simulation with regards to the obtained photocurrent is ∼10%.
B. O'Regan
The results reported represent the median of five sets of devices made on separate occasions from three different synthetic batches of CdSe totaling 57 individual solar cells. The maximum external quantum efficiency of each of these 57 devices are all within 10% relative to the median with the highest obtained efficiency at 59% all under ∼0.1 mW/cm 2 monochromatic illumination. Individual devices have been characterized repeatedly over the time scale of several months and showed no substantial change between measurements.
Supported by the National Renewable Energy Laboratory (grant XAD-9-18668-02) and the DOE (contracts DE-AC03-76SF00098 and DE-AC03-76SF00098). We are grateful to the Robert D. Ogg Electron Microscopy Laboratory at the University of California Berkeley for assistance with the TEM work and providing cross sections. The authors also would like to thank G. Whiting and W. Libby for experimental assistance and L. Manna D. Milliron J. Frechet and C. Pitois for their valuable discussions. W.U.H. thanks the Natural Sciences and Engineering Research Council of Canada for a fellowship.