Comparison of short and long wavelength absorption electron donor materials in C60-based planar heterojunction organic photovoltaics

Buckminsterfullerene, C-60-based planar heterojunction (PHJ) organic photovoltaics (OPVs) have been created using a short wavelength absorption (lambda(max) = 490 nm) electron-donating bis(naphthylphenylaminophenyl)fumaronitrile (NPAFN). NPAFN exhibits a hole mobility greater than 0.07 cm(2) V-1 s(-1) as determined by its field-effect transistor. It can be attributed to such hole mobility that enables a thin layer (<10 nm) NPAFN in PHJ OPV, ITO/NPAFN/C-60/bathocuproine/Al. Because of the low lying HOMO energy level (5.75 eV) of NPAFN and relatively high ionization potential ITO (similar to 5.58 eV), such OPVs exhibit a very high open circuit voltage of similar to 1.0 V, relatively high fill factor of 0.60, and a relatively high shunt resistance of 1100 Omega cm(-2), which all compensate for a relatively low short circuit current of 3.15 mA cm(-2) due to the short absorption wavelength and inferred short exciton diffusion length of NPAFN. Altogether, NPAFN OPVs display a power conversion efficiency (eta(PC)) of 2.22%, which is better than other long wavelength absorption materials in similar PHJ OPVs, such as pentacene (lambda(max) 670 nm, HOMO 5.12 eV, eta(PC) 1.50%) and copper phthalocyanine (lambda(max) 624, 695 nm, HOMO 5.17 eV, eta(PC) 1.43%). Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.