Efficient, sensitive and wavelength-selective light detection has become central to modern consumer electronics, and also in science and technology. Photodetectors based on crystalline inorganic elemental materials such as silicon and compound semiconductors are the core of today’s photodetectors. However, a new trend has begun: next generation semiconductors such as organics, perovskites, and nanocrystals are now becoming increasingly interesting candidates for low noise, color-selective, efficient photodetection. As a promising candidate for next-generation photodetectors, solution-processed organic-based photodetectors (OPDs) provide the opportunity to develop innovative, low cost, and large-area imaging technologies for industrial applications. Thanks to their advantages as a large range of available materials, a tunable spectral response range, compatibility with lightweight flexible substrates and device architectures, they have gained a continuous increasing interest.

OPDs have drawn extensive research efforts due to their tailorable spectral response but to detect specific signals under low illumination intensities, OPD devices should deliver a low dark current and a relatively high sensitivity. The spectral response can be either broadband or narrowband. Benefiting from advanced material synthesizing techniques, narrowband OPDs with many improved properties have been emerging in recent years, with promising features like high selectivity of the target wavelength compared to broadband counterparts. In addition and to avoid specific synthesis of the photo-absorbing materials, the charge collection narrowing (CCN) can be applied.^[1] Starting from a broadband absorbers often used in organic solar cells (OSCs), narrowband OPDs are obtained by the realization of thick layers (700 nm), which flattened the spectral response, reduced the dark current and decreased performance variations.

In the present study, broadband and narrowband OPDs were realized with an active layer composed of PM6/ITIC-4F bulk heterojunction blend. During the past years, the development of non-fullerene acceptors (NFA) led to an impressive improvement of the OSC power conversion efficiency to above 18%.^[2] This new family of electron accepting materials with absorption edges up to 1100 nm has great potential for both broadband and narrowband OPDs. Depending on the structure of the OPD device, normal or inverted, the switch between broadband and narrowband OPDs has been controlled by the donor:acceptor mass ratio, the final blend concentration, the film thickness or most notably by the post-annealing temperature. The impact and role of these parameters were studied by absorption and water contact angle measurements. The morphology and microstructure of thin films made by liquid deposition techniques were analyzed by AFM, Raman and X-ray diffraction.