Multication Tin‐Lead Perovskite Photodiodes with Engineered Lattice Strain for Ultrasensitive Broadband Photodetection

Abstract Tin‐lead alloyed perovskites with broadband absorption over 1000 nm, are suitable for UV‐vis‐NIR light detection that rivals the crystalline silicon semiconductors. These alloyed perovskites usually experience local lattice distortion and inherent lattice strain, which affect the electronic band structures and introduce detrimental trap states subsequently. To date, the lattice strain and its impact on the physical properties of tin‐lead alloyed perovskites are still less understood. Herein, it is shown that the lattice strain contributes substantially to the band edge electronic structure of multication tin‐lead alloyed perovskites by tilting the metal halide octahedral configuration. It has been found that the release of lattice strain heavily affects the band edge electronic structure of tin‐lead alloyed perovskites by reducing the band tail and shallow trap states as well as narrowing the bandgap simultaneously. Leveraging these insights, the optimized photodetector improves nearly 10‐fold the light detection limit to 0.49 pW cm −2 , achieving a record detectivity of >6 × 10 12 Jones in the near‐infrared range. The photodetectors on flexible substrates can be further integrated into an amplifier‐free wearable photoplethysmography device for real‐time heart rate and blood oxygen saturation monitoring, showing the promising potential for real applications.