Double‐side Interfacial Engineering of Hole Transport Layer Enables Efficient and Operationally Stable Colloidal Quantum Dot Solar Cells

Abstract Although lead sulfide (PbS) colloidal quantum dot (CQD) solar cells demonstrate excellent storage stability under ambient conditions, the operational stability is still rather poor for devices based on both organic or inorganic hole transport layer (HTL), seriously limiting their practical applications. In this work, it is find that both the CQD/polymer HTL bottom interface and the polymer HTL/electrode top interface are critical factors limiting device performance and operational stability. By proposing a double‐side interfacial engineering strategy to achieve surface energy matching and energy level grading, a high efficiency of 14.28% is realized using the classic P3HT HTL material, which is the highest reported efficiency for PbS CQD solar cells with organic HTLs. More importantly, the unencapsulated device can maintain 90% of its initial power (T 90 ) after ≈520 hours at the maximum power point (MPP) in ambient air, far exceeding the highest value previously reported in the literature (260 hours). This work provides new insights into the development of stable CQD‐based optoelectronic devices.