An effective bilayer cathode buffer for highly efficient small molecule organic solar cells

Novel organic/ultrathin low work function metal bilayer cathode buffers for small molecule organic solar cells are proposed. Ultrathin low work function metal layers possess a high built-in electric field for effective carrier extraction and a high cathode reflectivity for maximum absorption in the photoactive layers. This leads to a significant increase of short circuit current density and fill factor of cells. By integrating this bilayer cathode buffer with DTDCTB:C60 small molecular heterojunction, the device exhibits a high power conversion efficiency of up to 5.28%, which is an improvement of 22% compared to a device with a traditional single organic layer buffer.

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► A bilayer cathode buffer for small molecule solar cells has been demonstrated.
► Introduction of the buffer results in an increase of short circuit current density and fill factor.
► The buffer establishes a high built-in electric field for effective carrier extraction.
► The devices adopting the buffer show high power conversion efficiency of 5.28%.