Photoquenching-by-Photocharging: A Single Process of Failure of Oxygen-Exposed InP/ZnSe Quantum Dots

Reliability is an essential aspect of emerging optoelectronic technologies based on colloidal quantum dots (QDs). Even so, the fundamental chemical processes that deteriorate the performance of QD-based devices remain poorly understood. Here, we identify a single process of failure that leads to photoluminescence (PL) quenching of InP-based QDs under continuous illumination in an O₂-containing atmosphere. We first demonstrate that a rapid loss of PL efficiency occurs under combined O₂/light exposure. While no noticeable changes in chemical composition of the QDs occur, we show by femtosecond transient absorption a direct correlation between the PL quenching and the buildup of a population of charged QDs, in which nonemissive trions are formed after photoexcitation. Using electron paramagnetic resonance, we relate QD charging to the transfer of a photoexcited electron to physisorbed O₂, thereby forming superoxide anions. Understanding this single process of failure is critical for enhancing the reliability of devices using InP-based QDs for photoluminescent color conversion and electroluminescent light emission.