As a promising candidate for next-generation photodetectors, organic photodetectors (OPDs) outperform the commercial inorganic photodetectors in terms of solution and large-area processability, mechanical flexibility, tunable spectral response range, low-cost manufacturing, and light weight. The OPDs with broadband spectral response attract an extensive attention due to their potential in wide application fields, such as flexible image sensing, surveillance, and health monitoring. In this review, recent advances in broadband OPDs are summarized as two sections: i) Photodiode type OPDs (PD-OPDs) based on thick-film strategy, ternary strategy, interfacial engineering, and multilayered strategy. ii) Photomultiplication type OPDs (PM-OPDs) with traps in active layer, traps in interfacial layer, and charge blocking layer. Some real applications on image sensors and photoplethysmography (PPG) sensors are also introduced on the basis of broadband OPDs. New insights on developing the broadband OPDs are put forward for improvement of broadband OPDs.

Narrowband photomultiplication-type organic photodetectors (PMOPDs) are realized with poly(3-hexylthiophene-2,5-diyl) (P3HT) as the optical field adjusting (OFA) layer and transfer-printed P3HT: [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) (50:1, w/w) as the photomultiplication (PM) layer. The thickness of the OFA layers is adjusted to optimize interfacial trapped electron distribution and density, which determines the external quantum efficiency (EQE) and spectral response range of PMOPDs. Narrowband PMOPDs with 2.5 µm thick P3HT as the OFA layer exhibit two narrow response peaks at 350 and 660 nm, and the corresponding EQE values at 350 and 660 nm are 180% and 760% under an applied bias of −20 V. A wide bandgap polymer poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (P-TPD) is deliberately incorporated into OFA layer for adjusting interfacial trapped electron distribution near Al electrode. Narrowband PMOPDs exhibit only one response peak at 660 nm with the enhanced EQE value of 1120% under the same bias. The enhanced EQE of PMOPDs with P-TPD is primarily attributed to the increased hole tunneling injection and transport, which can be ascribed to the enhanced trapped electron density near the Al electrode and the improved hole mobility, respectively. Clearly resolved images can be obtained from the imaging system with the narrowband PMOPDs as sensing pixel without any current preamplifier, indicating the promising potential of PMOPDs in imaging sense.

Wide bandgap polymer D18 with narrow photon harvesting in visible light range and small molecule N3 with near‐infrared photon harvesting are adopted for building semitransparent organic photovoltaics (OPVs). To find out the optimal D18:N3 weight ratio for semitransparent OPVs, series of opaque OPVs are built with a varied D18:N3 weight ratio. The power conversion efficiency (PCE) and fill factor can be maintained over 16% and 77% in the D18:N3 (0.7:1.6, wt/wt) based opaque OPVs, respectively. The average visible transmittance (AVT) of the corresponding blend films can be achieved over 50%, demonstrating the great potential in fabricating efficient semitransparent OPVs. The semitransparent OPVs based on D18:N3 (0.7:1.6, wt/wt) are fabricated by using 1 nm Au/(10, 15, 20 nm) Ag as cathode. The thickness of Ag layers is varied to balance the optical properties and electrical properties of semitransparent top electrode. The semitransparent OPVs with 10 nm Ag achieve the highest light utilization efficiency of 2.90% with a PCE of 12.91% and an AVT of 22.49%, which should be among the best performance of reported semitransparent OPVs. This work demonstrates that the wide bandgap polymer donor with narrow photon harvesting in visible light range has great potential in preparing efficient semitransparent OPVs.

Broad response organic photodetectors (OPDs) with a photomultiplication (PM) effect are achieved with one absorber layer and one multiplication layer. The response range of the PM-OPDs is primarily determined by materials in the absorber layer, and the external quantum efficiency (EQE) of the PM-OPDs is mainly controlled by the multiplication layer. Here, double-layered PM-OPDs were designed with an ITO/ZnO/PM6:Y6/PC71BM:P3HT (100:5, w/w)/Au structure, where PM6:Y6 is employed as an absorber layer and PC71BM:P3HT is used as a multiplication layer. The optimal PM-OPDs exhibit a broad response covering 350–950 nm. Meanwhile, the optimal PM-OPDs exhibit the largest EQE value of ∼1200% and a maximum specific detectivity (D*) of ∼6.8 × 10–12 cm Hz1/2 W–1 under a 10 V bias. This double-layered approach may be a smart strategy for realizing PM-OPDs with an easily adjustable response range.

Ultraviolet (UV) narrowband photodetectors play a critical role in missile detection, flame monitoring, optical communication, etc. It is a great challenge to realize UV narrowband organic photodetectors due to wide photo-harvesting property of organic materials, especially for photomultiplication type organic photodetectors (PM-OPDs). In this work, a smart strategy is proposed to achieve UV narrowband response by coupling Fabry−Pérot microcavity with PM-OPDs. PM-OPDs are realized by using poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C 71 -butyric acid methyl ester (100:1, w/w) as active layers, exhibiting broadband response range covering from UV-vis region. Series of optical microcavities consisting of Ag/LiF/ Ag with UV spectral selectivity are prepared, which are employed to couple with the PM-OPDs for achieving UV narrowband response. The UV spectral selectivity of optical microcavity can be optimized by tuning the thickness of spacer layer and mirror layers, which can further regulate the photogenerated electron distribution near Al electrode to optimize the external quantum efficiency (EQE) spectra of the PM-OPDs coupled with optical microcavity. The optimized PM-OPDs coupled with optical microcavity exhibit EQE of 9300% at 350 nm and narrowband response with 33 nm full-width at halfmaximum under −15 V bias. This work indicates that PM-OPDs coupled with optical microcavity should be an efficient strategy for achieving UV narrowband response.