There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

While the field of perovskite-based optoelectronics has mostly been dominated by photovoltaics, light-emitting diodes, and transistors, semiconducting properties peculiar to perovskites make them interesting candidates for innovative and disruptive applications in light signal detection. Perovskites combine effective light absorption in the broadband range with good photo-generation yield and high charge carrier mobility, a combination that provides promising potential for exploiting sensitive and fast photodetectors that are targeted for image sensing, optical communication, environmental monitoring or chemical/biological detection. Currently, organic–inorganic hybrid and all-inorganic halide perovskites with controlled morphologies of polycrystalline thin films, nano-particles/wires/sheets, and bulk single crystals have shown key figure-of-merit features in terms of their responsivity, detectivity, noise equivalent power, linear dynamic range, and response speed. The sensing region has been covered from ultraviolet-visible-near infrared (UV-Vis-NIR) to gamma photons based on two- or three-terminal device architectures. Diverse photoactive materials and devices with superior optoelectronic performances have stimulated attention from researchers in multidisciplinary areas. In this review, we provide a comprehensive overview of the recent progress of perovskite-based photodetectors focusing on versatile compositions, structures, and morphologies of constituent materials, and diverse device architectures toward the superior performance metrics. Combining the advantages of both organic semiconductors (facile solution processability) and inorganic semiconductors (high charge carrier mobility), perovskites are expected to replace commercial silicon for future photodetection applications.

Perovskite-based photodetectors: materials and devices

The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.

https://arxiv.org/pdf/cond-mat/9709060.pdf

Intermediate-spin state and properties of LaCoO_3

Perovskite photodetectors (PPDs), which combine the advantages of perovskite semiconductor materials with superior optical and electronic properties and solution-processed manufacturing, have emerged as a new class of revolutionary optoelectronic devices with potential for various practical applications. Encouraged by the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of perovskite materials with interesting optoelectronic properties, increasing research attention is focused on the development of high performance PPDs. In this review, the recent progress on emerging PPDs is comprehensively summarized from the perspective of device physics and materials science. The strategies for extending the spectral response range of PPDs and improving the performance of devices are investigated. Furthermore, the methods for realizing narrowband photodetectors are also discussed, where filter-free and self-filter narrowband PPDs are achieved based on the concept of charge collection narrowing. Meanwhile, the promising future directions in this research field are proposed and discussed, including multifunctional PPDs, perovskite–organic hybrid photodetectors, flexible and transparent PPDs, self-powered PPDs, and photodetector systems and arrays. This review provides valuable insights into the current status of highly sensitive PPDs and will spur the design of new structures and devices to further enhance their photo-detection performances and meet the need of versatility in practical application.

Recent progress on highly sensitive perovskite photodetectors

Multi-functional organic field-effect transistors (OFETs), an emerging focus of organic optoelectronic devices, hold great potential for a variety of applications. This report introduces recent progress on multi-functional OFETs including OFETs based sensors, phototransistors, light-emitting transistors, memory cells, and magnetic field-effect OFETs. Key strategies towards multi- functional integration of OFETs, which involves the exploration of functional materials, interfaces modifications, modulation of condensed structures, optimization of device geometry, and device integration, are summarized. Furthermore, remaining challenges and perspectives are discussed, giving a comprehensive overview of multi-functional OFETs.

Multi-functional integration of organic field-effect transistors (OFETs): advances and perspectives.

Bending strain induced photocurrent crossover from positive to negative in the flexible organic phototransistors

The utility model discloses the design and the manufacturing method of a homotype planar heterojunction photosensitive organic field effect transistor. The homotype planar heterojunction photosensitive organic field effect transistor comprises a substrate, a grid electrode, a gate medium, an organic carrier transport layer, an organic light-sensitive layer, a drain electrode and a source electrode. The organic light-sensitive layer achieves a function of generating photo-generated carriers, and is required to have high photosensitivity or photo-generated carrier generation efficiency instead of high mobility. The organic carrier transport layer achieves a function of transporting the photo-generated carriers, and is required to have high mobility instead of high photosensitivity. The structure of the homotype planar heterojunction photosensitive organic field effect transistor greatly expands the selection range of organic materials. On one hand, the generation efficiency of the photo-generated carriers is improved, and on the other hand, the mobility of organic carriers is improved. Thus, the performances of the homotype planar heterojunction photosensitive organic field effect transistor can be effectively improved.

Homotype planar heterojunction photosensitive organic field effect transistor

In this paper, low-cost rectifier based on an organic diode for use in organic radio frequency identification (RFID) tags is proposed. Pentacene is the electroactive layer, with 7,7,8,8-tetracyanoquinodimethane (TCNQ) modified low-cost copper (Cu) and aluminum (Al) as the Ohmic and Schottky contacts, respectively. Hole injection barrier between Cu and pentacene can be decreased by forming the self-assembled layers of Cu-TCNQ. The diode shows a high rectification ratio of approximately 2×106 at 5V and the organic diode based rectifier circuit generated a dc output voltage of approximately 2V at 13.56MHz, using an input ac signal with zero-to-peak voltage amplitude of 5 V. The results indicate that chemical modification of the low-cost electrodes could be an efficient way toward low-cost high performance organic electronics devices.

Low-cost 13.56MHz Rectifier Based on Organic Diode

The invention discloses a designing and manufacturing method of a bipolar organic photosensitive field-effect tube. A current carrier barrier layer is added between a source electrode -organic semiconductor channel and a drain electrode -organic semiconductor channel of a common structure organic photosensitive field-effect tube, light currents are effectively increased, and dark currents are effectively reduced. The current carrier barrier layer is divided into an electronic barrier layer and a hole barrier layer. For a p-type organic photosensitive channel, high power function metal is chosen to be used as a source electrode and a drain electrode, and low HOMO energy level n-type materials such as C60 are used as the hole barrier layer. For an n-type organic photosensitive channel, low power function metal is chosen to be used as the source electrode and the drain electrode, high LUMO energy level p-type materials such as copper phthalocyanine are used as the electronic barrier layer. The bipolar organic photosensitive field-effect tube manufactured according to the technical scheme structurally comprises a substrate, a grid electrode, gate media, an organic photosensitive channel, the current carrier barrier layer, the drain electrode and the source electrode. A p-type/n-type heterojunction is formed between the current carrier barrier layer and the organic photosensitive channel, on one hand, the impedance between the drain electrode and the source electrode is increased when no light exists and so that dark currents are lowered; on the other hand, dissociation of photoproduction excitons is facilitated so that the photovoltaic conversion efficiency can be improved. Therefore, the bipolar organic photosensitive field-effect tube has the advantages of being high in ratio of light currents to dark currents.

Bipolar organic photosensitive field-effect tube

The invention discloses a structure and manufacturing method of a Schottky contact organic photosensitive field-effect transistor. The manufacturing method comprises the following steps that low-work function metal is used as a drain electrode and a source electrode for a p-type organic photosensitive channel material so that a source electrode-organic photosensitive channel material and a drain electrode-organic photosensitive channel material can form hole Schottky contact, and high-work function metal is used as a drain electrode and a source electrode for an n-type organic photosensitive channel material so that a source electrode-organic photosensitive channel material and a drain electrode-organic photosensitive channel material can form electronic Schottky contact. The source electrodes, the drain electrodes and organic photosensitive channels form Schottky contact, therefore, the impedance between the drain electrodes and the source electrodes without illumination is increased, dark currents are lowered greatly, and photocurrents are reduced only slightly. Therefore, the Schottky contact organic photosensitive field-effect transistor manufactured according to the manufacturing method has the advantages that the dark currents are low, and the ratio of the photocurrents to the dark currents is high.

Yingquan Peng

Papers

Bending strain induced photocurrent crossover from positive to negative in the flexible organic phototransistors

Homotype planar heterojunction photosensitive organic field effect transistor

Low-cost 13.56MHz Rectifier Based on Organic Diode

Bipolar organic photosensitive field-effect tube

Schottky contact organic photosensitive field-effect transistor