Abstract
Charge separation efficiency is a crucial parameter for photovoltaic devices—polymers consisting of alternating electron-rich and electron-deficient parts can achieve high such efficiencies, for instance, together with a fullerene electron acceptor. This offers a viable path toward solar cells with organic bulk heterojunctions. Here, we measured the charge-transfer times in the femtosecond and attosecond regimes via the decay of sulfur 1s X-ray core-excited states (with the core-hole clock method) in blends of a low-band gap polymer {PCPDTBT [poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]]} consisting of a cyclopentadithiophene electron-rich part and a benzothiadiazole electron-deficient part. The constituting parts of the bulk heterojunction were varied by adding the fullerene derivative PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) (weight ratio of polymer/PCBM as 1:0, 1:1, 1:2, and 1:3). For low-energy excitations, the charge-transfer time ...
Highlights
Organic photovoltaic (OPV) devices offer a route toward cheap solar energy harnessing and are an active research field where the interplay between chemistry and physics is the key to push device performance and longevity.[1−3] As in other branches ofelectronics, polymer-based OPVs are attractive alternatives to silicon technology because of their relatively low cost, flexibility, coloration, and semitransparency.they are nontoxic and recyclable
XPS and hard X-ray photoelectron spectroscopy (HAXPES) measurements show that interface dipoles are almost absent at the PCBM−PCPDTBT interface
The transfer of an excited electron in the lowest unoccupied molecular orbital (LUMO) of PCPDTBT to the LUMO of PCBM should be possible for all mixing ratios
Summary
Organic photovoltaic (OPV) devices offer a route toward cheap solar energy harnessing and are an active research field where the interplay between chemistry and physics is the key to push device performance and longevity.[1−3] As in other branches of (opto)electronics, polymer-based OPVs are attractive alternatives to silicon technology because of their relatively low cost, flexibility, coloration, and semitransparency.
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