Inverted, semitransparent small molecule photovoltaic cells

Abstract

We demonstrate semitransparent small molecule organic photovoltaic (OPV) cells based on inverted mixed and hybrid planar-mixed heterojunction (PM-HJ) structures comprised of a neat acceptor layer located beneath the donor/acceptor mixed region. The fill factor increases from 0.53 ± 0.01 for the mixed HJ to 0.58 ± 0.01 for the PM-HJ due to reduced series resistance, whereas the internal quantum efficiency increases from an average of 75% to 85% between the wavelengths of λ = 450 nm and 550 nm. The inverted, semitransparent PM-HJ cell achieves a power conversion efficiency of PCE = 3.9% ± 0.2% under simulated AM1.5G illumination at one sun intensity with an average optical transmission of T¯ = 51% ± 2% across the visible spectrum, corresponding to > 10% improvement compared with the mixed HJ cell. We also demonstrate an inverted semitransparent tandem cell incorporating two PM-HJ sub-cells with different absorption spectra. The tandem cell achieves a PCE = 5.3% ± 0.3% under simulated AM1.5G at one sun intensity with T¯ = 31% ± 1% across the visible. Almost identical efficiencies are obtained for tandem cells illuminated via either the cathode or anode surfaces.