Heterojunction Derived Efficient Charge Separation for High Sensitivity Self-Powered Flexible Photodetectors toward Real-Time Heart Rate Monitoring.

Real-time and accurate heart rate monitoring is crucial in the field of disease prevention and early diagnosis. Compared with the conventional rigid heart rate sensors, wearable flexible devices have unique advantages, such as convenient, high comfortable to the skin, and low data extraction errors. Currently, the available flexible electronic devices encounter with large power consumption, low detectivity, and slow response time, restricting their further commercial applications. Herein, flexible self-powered photodetectors (PDs) are developed by the synergistic strategy of engineering CsPbI₃:Ho³⁺@SnS quantum dots (QDs) p-n heterojunctions and doping SnS QDs into spiro-OMeTAD hole transport layer (HTL). The designing CsPbI₃:Ho³⁺@SnS QDs p-n heterojunctions as the photosensitive layer to effectively enhance the built-in field, reduce defect density, and boost the charge separation efficiency. Meanwhile, the high hole mobility and suitable energy band structure of p-type SnS QDs are doped into spiro-OMeTAD HTL, which can improve the hole extraction, and balance electron and hole mobilities. Such flexible self-powered PDs exhibit excellent sensitivity and stability with high responsivity (0.58 A W^-1) and detectivity (1.13×10¹³ Jones), and fast response time (98.8 µs). The flexible self-powered PDs are further integrated with the light-emitting diodes (LEDs) as a photoplethysmography (PPG) system, realizing real-time and accurate heart rate monitoring.