Integration of polyoxometalate clusters with self-assembled monolayer for efficient and robust organic solar cells

Organic solar cells (OSCs) with p-i-n structure have achieved rapid progress in efficiency recently. However, the p-i-n structure suffers from inferior stability owing to the hole-transporting layers (HTLs) that usually encounter unfavorable phase separation or insufficient anode coverage under aging. Herein, we develop a subtle strategy that integrates self-assembled monolayer (SAM) and polyoxometalate (POM) into an intimately intercalating composite as HTL. This sequentially deposited composite (SDC) shows a unique distribution pattern, with SAM enriched at the bottom and POM functioned as both void-filler and top-surface passivator, enabling improved surface contact. Moreover, the formation of multiple doping pathways increases the charge extraction in OSCs. The SDC-HTL strategy not only results in a much higher device efficiency, but it significantly impedes the photovoltage and fill-factor degradation in p-i-n OSCs under multiple stresses. This work demonstrates the superiority of integrating multiple ultra-thin HTLs for improving the interfacial contact between functional layers, thus addressing the instability in OSCs.