High Performance Self‐Powered Perovskite Quantum Dots Photodetectors Enabled by Cr³⁺ Doping and MXene Interfacial Engineering for Precise Chlorophyll‐a Monitoring

Accurate and rapid monitoring of chlorophyll‐ a (Chl‐ a ) concentrations is essential for assessing phytoplankton abundance and water quality. However, existing methods lack a combination of cost‐effectiveness, operational simplicity, and real‐time ultrasensitive detection capability. In this study, self‐powered perovskite quantum dots (PQDs) photodetectors (PDs) with a high responsivity of 186.9 mA W −1 and detectivity of 1.85 × 10 12 cm Hz 1/2 W −1 are developed through Cr 3+ doping and MXene interfacial engineering, offering strong potential for Chl‐ a concentration monitoring based on the Beer–Lambert law. Cr 3+ doping significantly enhances the photoluminescence quantum yields to 92.2%, reduces the defect density, and improves the stability of CsPbI 3 PQDs. Meanwhile, Nb 2 CT x MXene nanosheets serve as an efficient “carrier bridge” between the electronic transport layers and PQDs interface of the PDs, effectively reducing carrier accumulation and enhancing charge extraction and transport. Moreover, the optimized self‐powered PDs exhibit superior air, UV, and thermal stabilities compared with the pristine devices. As a proof of concept, the self‐powered PDs are employed to monitor the Chl‐ a concentration in water, showing a good linear response in the range of 0.05–1 mg L −1 and low detection limitation. This study presents a novel approach for developing high‐performance self‐powered PDs and advanced water pollution monitoring.