Highly Efficient And Stable ITO-free Organic Solar Cells Based on Squaraine N-Doped Quaternary Bulk Heterojunction.

Simultaneously achieving high efficiency and robust device stability remains a significant challenge for organic solar cells (OSCs). Solving this challenge is highly dependent on the film morphology of the bulk heterojunction (BHJ) photoactive blends; however, there is a lack of rational control strategy. Herein, we show that the molecular crystallinity and nanomorphology of nonfullerene-based BHJ can be effectively controlled by a squaraine-based doping strategy, leading to an increase in device efficiency from 17.26% to 18.5% when doping 2 wt.% squaraine into the PBDB-TF:BTP-eC9:PC 71 BM ternary BHJ. The efficiency is further improved to 19.11% (certified 19.06%) using an ITO-free column-patterned microcavity (CPM) architecture. Combined with interfacial modification, CPM quaternary OSC excitingly shows an extrapolated lifetime of ∼23 years based on accelerated aging test, with the mechanism behind enhanced stability well studied. Furthermore, a flexible OSC module with a high and stable efficiency of 15.2% and an overall area of 5 cm 2 has been successfully fabricated, exhibiting a high average output power for wearable electronics. Our work demonstrates OSCs with new design of BHJ and device architecture are highly promising to be practical relevance with excellent performance and stability. This article is protected by copyright. All rights reserved.