Inverted Organic Solar Cells with Improved Performance using Varied Cathode Bu?er Layers

Organic solar cells with inverted planar heterojunction structure based on subphthalocya-nine and C₆₀ were fabricated using several kinds of materials as cathode buffer layer (CBL), including tris-8-hydroxy-quinolinato aluminum (Al_q3), bathophenanthroline (Bphen), bathocuproine, 2,3,8,9,14,15-hexakis-dodecyl-sulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA), and an inorganic compound of Cs₂CO₃. The influence of the lowest unoccupied molecular orbital level and the electron mobility of organic CBL on the solar cells perfor-mance was compared. The results showed that Al_q3, Bphen, and HATNA could significantly improve the device performance. The highest efficiency was obtained from device with an-nealed HATNA as CBL and increased for more than 7 times compared with device without CBL. Furthermore, the simulation results with space charge-limited current theory indicated that the Schottky barrier at the organic/electrode interface in inverted OSC structure was reduced for 27% by inserting HATNA CBL.