Toward Air Stability of Efficient Filter‐Free Band‐Selective Organic Photodetectors Based on Bulk Heterojunction: Avoiding Environmental Degradation with Atomic Layer Deposition Encapsulation

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To detect the band‐specific optical signals used in many fields, it is necessary to develop spectrally selective photodetection. For such wavelength‐selective photodetection or color discrimination, organic photodetectors (OPDs) can offer significant benefits as low temperature and solution processability, chemical versatility, and specific spectral detection range. However, to avoid commonly used filters, the design of a narrowing approach that simultaneously achieves a selective detection range with a bandwidth of less than 50 nm and a spectral response of over 20% remains a challenge. OPDs based on charge‐collection‐narrowing principle can provide these features. In this approach, the detection window can be selected to match the absorption onset of the junction materials used in the bulk heterojunction layer. Herein, filter‐free band‐selective OPDs are realized based on PM6:PC70BM blends as state of the art. Fine adjustment over a bandwidth of 42 nm to be highly selective at 677 nm with a quantum efficiency of 48.4% under an inverse low bias of −2 V is reached. In addition, using a noninvasive and nondestructive encapsulation technique, it is demonstrated that these OPDs fully retain their high selective peak after 30 days storage in air.