Improved Light Harvesting and Improved Efficiency
by Insertion of an Optical Spacer (ZnO) in Solution-Processed Small-Molecule
Solar Cells
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Abstract
We
demonstrate that the power conversion efficiency can be significantly
improved in solution-processed small-molecule solar cells by tuning
the thickness of the active layer and inserting an optical spacer
(ZnO) between the active layer and the Al electrode. The enhancement
in light absorption in the cell was measured with UV–vis absorption
spectroscopy and by measurements of the photoinduced carriers generation
rate. The ZnO layer used to improve the light-harvesting increases
the charge collection efficiency, serves as a blocking layer for holes,
and reduces the recombination rate. The combined optical and electrical
improvements raise the power conversion efficiency of solution-processed
small-molecule solar cells to 8.9%, that is, comparable to that of
polymer counterparts