Organic solar cells with sensitivity extending into the near infrared

We describe an organic photovoltaic cell based on a tin(II) phthalocyanine (SnPc)∕C60 donor/acceptor heterojunction with sensitivity at wavelengths of λ>900nm. We find that the low hole mobility in polycrystalline thin films of SnPc, μh=(2±1)×10−10cm2∕Vs, prevents the use of thick layers, leading to low fill factors and therefore low-power conversion efficiencies. However, owing to its large absorption coefficient, a 50-Å-thick layer of SnPC yields solar cell external quantum efficiencies of up to 21% at λ=750nm. With the double heterostructure of indium-tin oxide/100Å copper phthalocyanine/50Å SnPc∕540Å C60∕75Å bathocuproine/Ag, we obtain a power conversion efficiency of (1.0±0.1)% under 1 sun standard AM1.5G solar illumination and efficiencies of (1.3±0.1)% under intense (10 suns) standard AM1.5G solar illumination.