Major growth in the image sensor market is largely as a result of the expansion of digital imaging into cameras, whether stand-alone or integrated within smart cellular phones or automotive vehicles. Applications in biomedicine, education, environmental monitoring, optical communications, pharmaceutics and machine vision are also driving the development of imaging technologies. Organic photodiodes (OPDs) are now being investigated for existing imaging technologies, as their properties make them interesting candidates for these applications. OPDs offer cheaper processing methods, devices that are light, flexible and compatible with large (or small) areas, and the ability to tune the photophysical and optoelectronic properties − both at a material and device level. Although the concept of OPDs has been around for some time, it is only relatively recently that significant progress has been made, with their performance now reaching the point that they are beginning to rival their inorganic counterparts in a number of performance criteria including the linear dynamic range, detectivity, and color selectivity. This review covers the progress made in the OPD field, describing their development as well as the challenges and opportunities.

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

In order to develop high performance polymer solar cells (PSCs), full exploitation of the sun-irradiation from ultraviolet (UV) to near infrared (NIR) is one of the key factors to ensure high photocurrents and thus high efficiency. In this review, five of the effective design rules for approaching LBG semiconducting polymers with high molar absorptivity, suitable energy levels, high charge carrier mobility and high solubility in organic solvents are overviewed. These design stratagems include fused heterocycles for facilitating π-electron flowing along the polymer backbone, groups/atoms bridging adjacent rings for maintaining a high planarity, introduction of electron-withdrawing units for lowering the bandgap (Eg), donor–acceptor (D–A) copolymerization for narrowing Eg and 2-dimensional conjugation for broadened absorption and enhanced hole mobility. It has been demonstrated that LBG semiconducting polymers based on electron-donor units combined with strong electron-withdrawing units possess excellent electronic and optic properties, emerging as excellent candidates for efficient PSCs. While for ultrasensitive photodetectors (PDs), which have intensive applications in both scientific and industrial sectors, sensing from the UV to the NIR region is of critical importance. For polymer PDs, Eg as low as 0.8 eV has been obtained through a rational design stratagem, covering a broad wavelength range from the UV to the NIR region (1450 nm). However, the response time of the polymer PDs are severely limited by the hole mobility of LBG semiconducting polymers, which is significantly lower than those of the inorganic materials. Thus, further advancing the hole mobility of LBG semiconducting polymers is of equal importance as broadening the spectral response for approaching uncooled ultrasensitive broadband polymer PDs in the future study.

Low bandgap semiconducting polymers for polymeric photovoltaics

Second near-infrared photothermal therapy (NIR-II PTT, 1000-1500 nm) has recently emerged as a new phototherapeutic modality with the advantages of deeper penetration, less energy dissipation and minimal normal-tissue toxicity over traditional first NIR PTT (750-1000 nm). However, suboptimal photothermal conversion and limited therapeutic efficacy remain the major challenges for NIR-II PTT. With the convergence in materials science, nanomedicine and biology, multifunctional NIR-II photothermal inorganic or organic materials have been extensively developed to combine NIR-II PTT with other therapeutic modalities for improved efficacies in treating life-threatening diseases including cancer and infection. This review summarizes the recent advances of NIR-II photothermal combinational theranostics pertinent to chemotherapy, immunotherapy, radiotherapy, and photodynamic, sonodynamic, chemodynamic, gene, gas, ionic, vascular and magnetothermal therapy. Potential obstacles and perspectives for future research and clinical translation of this new theranostic modality are also discussed.

Second near-infrared photothermal materials for combinational nanotheranostics

Development of Organic Semiconductor Photodetectors: From Mechanism to Applications

In recent times, fused aromatic diketopyrrolopyrrole (DPP)-based functional semiconductors have attracted considerable attention in the developing field of organic electronics. Over the past few years, DPP-based semiconductors have demonstrated remarkable improvements in the performance of both organic field-effect transistor (OFET) and organic photovoltaic (OPV) devices due to the favorable features of the DPP unit, such as excellent planarity and better electron-withdrawing ability. Driven by this success, DPP-based materials are now being exploited in various other electronic devices including complementary circuits, memory devices, chemical sensors, photodetectors, perovskite solar cells, organic light-emitting diodes, and more. Recent developments in the use of DPP-based materials for a wide range of electronic devices are summarized, focusing on OFET, OPV, and newly developed devices with a discussion of device performance in terms of molecular engineering. Useful guidance for the design of future DPP-based materials and the exploration of more advanced applications is provided.

Developments of Diketopyrrolopyrrole-Dye-Based Organic Semiconductors for a Wide Range of Applications in Electronics.

Liver tumor is one of the most lethal cancers due to its low ratio of surgical resection, high recurrence rate, and invasiveness. Photothermal therapy (PTT) possesses many advantages for cancer the...

Tailor-Made Semiconducting Polymers for Second Near-Infrared Photothermal Therapy of Orthotopic Liver Cancer.

A series of weak donor-strong acceptor polymers containing two different electron-deficient units (diketopyrrolopyrrole and thienoisoindigo) are synthesized and used in broad-response and high-detectivity polymer photodetectors. By adjusting the composition ratio of the two acceptors, the absorption spectra, energy levels, molecular stacking, and film morphology are affected, which in turn influence the photodetector performance. With increased thienoisoindigo component, the HOMO energy levels shift from -5.41 to -4.76 eV, and the LUMO energy levels are nearly unchanged, corresponding to reduced bandgaps and red-shifted absorption spectra. 1,8-Diiodooctane additive shows greatly impact on the film morphology, which affects the photodetector performance significantly. Going from P1 to P5, the detectivity decreases, but the response range increases. The photodetector based on P4 exhibits detectivity of greater than 10(11) Jones in a broad spectral region of 300-1200 nm, which is really promising for UV-vis-NIR light detection.

Optimization of Broad-Response and High-Detectivity Polymer Photodetectors by Bandgap Engineering of Weak Donor-Strong Acceptor Polymers

A novel donor unit dithienobenzotrithiophen (DTBTT) was designed and utilized in the synthesis of a series of donor–acceptor (D–A) polymers with the thienoisoindigo-based acceptor. The relationships between the structure of polymers and the absorption spectra, electrochemistry properties, hole mobility, and photovoltaic properties of these polymers have been studied. The results showed that low-bandgap D–A polymers containing DTBTT are suitable for use in broadband polymer photodetectors. Polymer photodetectors exhibited a specific detectivity (D*) in the order of 1012 Jones, low dark current and photoresponsivity at the wavelengths from 300 to 1600 nm.

Jinfeng Han

Papers

Tailor-Made Semiconducting Polymers for Second Near-Infrared Photothermal Therapy of Orthotopic Liver Cancer.

Optimization of Broad-Response and High-Detectivity Polymer Photodetectors by Bandgap Engineering of Weak Donor-Strong Acceptor Polymers

Low-bandgap donor–acceptor polymers for photodetectors with photoresponsivity from 300 nm to 1600 nm

Low-Bandgap Polymers for High-Performance Photodiodes with Maximal EQE near 1200 nm and Broad Spectral Response from 300 to 1700 nm

Dichlorinated Dithienylethene-Based Copolymers for Air-Stable n-Type Conductivity and Thermoelectricity