Organic solar cells with sensitivity extending into the near infrared

We describe an organic photovoltaic cell based on a tin(II) phthalocyanine $\left(\mathrm{Sn}\mathrm{Pc}\right)∕{\mathrm{C}}_{60}$ donor/acceptor heterojunction with sensitivity at wavelengths of $\lambda >900\mathrm{nm}$ . We find that the low hole mobility in polycrystalline thin films of SnPc, ${\mu }_h=(2\pm 1)\times {10}^{-10}{\mathrm{cm}}^2∕\mathrm{V}\mathrm{s}$ , 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 $50\text{-}\mathrm{\AA }$ -thick layer of SnPC yields solar cell external quantum efficiencies of up to 21% at $\lambda =750\mathrm{nm}$ . With the double heterostructure of indium-tin oxide/$100\mathrm{\AA }$ copper phthalocyanine/$50\mathrm{\AA }$ $\mathrm{Sn}\mathrm{Pc}∕540\mathrm{\AA }$ ${\mathrm{C}}_{60}∕75\mathrm{\AA }$ bathocuproine/Ag, we obtain a power conversion efficiency of $(1.0\pm 0.1)\%$ under 1 sun standard AM1.5G solar illumination and efficiencies of $(1.3\pm 0.1)\%$ under intense (10 suns) standard AM1.5G solar illumination.