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

Abstract

Buckminsterfullerene, C60-based planar heterojunction (PHJ) organic photovoltaics (OPVs) have been created using a short wavelength absorption (λmax=490nm) electron-donating bis(naphthylphenylaminophenyl)fumaronitrile (NPAFN). NPAFN exhibits a hole mobility greater than 0.07cm2V−1s−1 as determined by its field-effect transistor. It can be attributed to such hole mobility that enables a thin layer (<10nm) NPAFN in PHJ OPV, ITO/NPAFN/C60/bathocuproine/Al. Because of the low lying HOMO energy level (5.75eV) of NPAFN and relatively high ionization potential ITO (∼5.58eV), such OPVs exhibit a very high open circuit voltage of ∼1.0V, relatively high fill factor of 0.60, and a relatively high shunt resistance of 1100Ωcm−2, which all compensate for a relatively low short circuit current of 3.15mAcm−2 due to the short absorption wavelength and inferred short exciton diffusion length of NPAFN. Altogether, NPAFN OPVs display a power conversion efficiency (ηPC) of 2.22%, which is better than other long wavelength absorption materials in similar PHJ OPVs, such as pentacene (λmax 670nm, HOMO 5.12eV, ηPC 1.50%) and copper phthalocyanine (λmax 624, 695nm, HOMO 5.17eV, ηPC 1.43%).