Mitigating Carrier Accumulation for Highly Efficient and Stable Extended Shortwave Photodiode Based on PbSe Colloidal Quantum Dots

Extended shortwave (eSWIR: 2–2.8 µm) photodiodes based on PbSe colloidal quantum dots (CQDs) have emerged recently. Though the quality of eSWIR PbSe CQDs has been improved significantly, the PbSe CQD‐based photodiodes showed low external quantum efficiency (EQE) and poor stability under self‐driven photovoltaic mode, due to the residual reactive oxygen species (ROS) and carrier accumulation at interfaces. In this work, the ROS is removed by immerging the ZnO layer with 1,2‐ethanodithiol solvent before deposition of PbSe CQD layer, so that the storage stability of the photodiodes improved dramatically. On the other hand, a novel strategy is introduced to mitigate the carrier accumulation, in which a thin p‐type interlayer is inserted into the electron extraction interface. This strategy is universally effective in suppressing the carrier extraction barriers induced by Fermi level equilibration effects at interfaces. Finally, PbSe photodiodes achieve a record zero‐bias EQE of 17% in the eSWIR region. Due to the suppressed noise, the PbSe photodiodes in self‐driven mode demonstrate a specific detectivity of 5.7 Jones at the first excitonic peak of λ = 2.35 µm, which is comparable to self‐driven eSWIR photodiodes based on bulk InGaAs. Besides, this strategy also dramatically improved the working stability of the photodiodes.