Photodetectors are core components that convert optical signals into electrical signals and play an important role in the propagation of optical signals. The demand for high-performance photodetectors is increasingly significant in the high-tech industry. Photomultiplication-type organic photodetectors (PM-OPDs) are highly favored due to their unique advantages, such as external quantum efficiency (EQE)>100%, low dark current, low driving bias, light weight, and ease of integration. These devices have been under development for three decades. Traditional methods, such as collision excitation or collision ionization, have struggled to achieve the photomultiplication phenomenon due to the disorder of organic semiconductor materials and the high exciton binding energy, which has long been a technological bottleneck limiting the development of organic photodetectors.

PM-OPDs can be achieved by preparing the active layers with a donor-to-acceptor weight ratio of about 100∶1. This configuration creates electron traps, where acceptors are surrounded by donors. Photogenerated electrons are captured by the traps, inducing hole tunneling injection from the external circuit into the active layers to achieve the photomultiplication phenomenon. PM-OPDs exhibit single charge carrier transport, which helps suppress dark current. The spectral response range determines the wavelength range of detectable optical signals, defining the applicable scenarios and fields for photodetectors (Fig. 1). Based on their spectral response range, PM-OPDs can be divided into broad response or narrow response types. Broad response PM-OPDs typically cover the ultraviolet, visible, and near-infrared regions, capturing light signals at multiple wavelengths and providing rich electrical information (Fig. 3). These are expected to be applied in broad spectral applications, such as broad spectral communication, multispectral imaging, and environmental monitoring (Fig. 4). Narrow response PM-OPDs selectively detect light within a specific wavelength range, requiring a narrow and sharp spectral response range to extract useful signals from complex light environments. Over the past decade, we have explored effective methods for preparing both broad response and narrow response PM-OPDs. The spectral response range of the PM-OPDs can be controlled by adjusting the trapped charge distribution near the interface between the electrode and the active layers. The spectral response range of broad response PM-OPDs needs to be further expanded. For narrow response PM-OPDs, our research focuses on further narrowing their full width at half maximum (FWHM) and improving spectral rejection ratio (SRR). Currently, the broad response PM-OPDs with a spectral response range covering 300‒1100 nm have been obtained (Fig. 5). Narrow response PM-OPDs, with selective spectral response range in the ultraviolet, visible, and near-infrared regions, have been achieved (Fig. 8, Fig. 9). Notably, the FWHM of narrow response PM-OPDs can be suppressed at 27 nm. In general, the detection of optical signals requires the collaborative use of multiple photodetectors with different spectral response ranges. As a result, PM-OPDs with adjustable spectral response ranges have emerged (Fig. 11). These PM-OPDs offer two or more working modes, which can be flexibly switched according to specific application scenarios and requirements. The tunable spectral response range of PM-OPDs supports their application in high-sensitivity detection scenarios, with promising development prospects in the field of optoelectronic integration. We aim to provide an experimental basis and reference for further research on PM-OPDs with tunable spectral response ranges by introducing the working mechanism and analyzing the methods for adjusting the spectral response range.

We first elaborate on the working mechanism of PM-OPDs and analyze the fundamental factors that affect their spectral response range. Then, we introduce the preparation methods for broad response and narrow response PM-OPDs. For broad response PM-OPDs, we introduce three methods: narrow bandgap organic semiconductor material selection, the ternary strategy, and the double-layered scheme to extend the spectral response range. For narrow response PM-OPDs, we focus on the charge injection narrowing concept, analyzing methods from the perspectives of material selection and device structure. Finally, we summarize the research progress on PM-OPDs with adjustable spectral response ranges and explore potential ways to improve their performance. Research on adjusting the spectral response range of PM-OPDs not only optimizes the performance of organic photodetectors but also promotes advancements in organic optoelectronic semiconductor materials, preparation processes, and device structures.Continued research on tunable spectral response PM-OPDs will drive progress in related industries, including the development of organic optoelectronic semiconductor materials, optoelectronic devices, and optoelectronic systems. The tunable spectral response range of PM-OPDs enhances their reliability and stability in various light detection scenarios, promoting the development of optoelectronic detection technology and creating new opportunities for related industries in integrated optoelectronics.