Enhanced performance and stability of inverted organic solar cells by using novel zinc-benzothiazole complexes as anode buffer layers

Abstract

Performance of inverted bulk-heterojunction solar cells with widely used tris(8-quinolinolate)aluminium(III) (Alq₃) is compared with a series of novel zinc-benzothiazole (Znb₂) derivatives as buffer layer. The devices including a Znb₂ thin layer between the poly(3-hexylthiophene) (P3HT):C₆₁-butyric acid methyl ester (PCBM) blend and the Au anode show a significant improvement in the power conversion efficiency (η), which is enhanced by 30% compared to Alq₃cells. Moreover, by combining both Alq₃ and Znb₂ in the device as a double buffer layer prior to the metal electrode deposition, the efficiency improves by 40%. The reasons for the enhanced performance of Znb₂ cells are attributed to the efficient charge transport and electron/exciton blocking properties. Furthermore it is expected that the deposition of Znb₂ modifies the Au work function to facilitate the hole transport and collection at the anode, and encapsulate the P3HT/PCBM blend during the electrode deposition. The presented photovoltaic cells also show high stability in ambient air conditions over a period of 245 days, which evidences the need of Znb₂ buffer layers for long-term device durability.