Inverted polymer solar cells integrated with small molecular electron collection layer

Abstract An efficient inverted polymer solar cell (PSC) is reported by integrating a small molecular electron collection layer (ECL) between indium tin oxide (ITO) cathode and the photoactive layer of blended poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PCBM). The ECL is composed of a cesium carbonate-doped tris(8-hydroxyquinolinato) aluminum (Cs2CO3:Alq3) layer. As determined by photoelectron spectroscopy and electrical measurements, the Cs2CO3 doping induces suitable energy level alignment at the ITO/Cs2CO3:Alq3/PCBM interface and the increase in bulk conductivity of organic ECL, which are favorable to electron extraction through Cs2CO3:Alq3 to ITO cathode. In addition, optical simulation indicates that the Cs2CO3:Alq3 layer can act as an optical spacer to modulate the region of highest incident light intensity within the photoactive layer, where absorption and charge dissociation are efficient. The inverted PSC with an optimized Cs2CO3:Alq3 ECL exhibits a power conversion efficiency of 4.83%. The method reported here provides a facile approach to achieve high-performance inverted PSCs at low processing temperature.