Plastic Near‐Infrared Photodetectors Utilizing Low Band Gap Polymer

Abstract

Organic photodetectors (PDs) have been the subject of extensive research in the past decade due to several inherent advantages: large-area detection, wide selection of materials, and low-cost fabrication on flexible substrates. High external quantum efficiency (EQE) [1,2] , full-color [3,4] , fast-response [5,6] , and position-sensitive [7] PDs have been reported in the past.However, there are few reports on organic near-infrared photodetectors (NIR-PDs) in spite of their tremendous potential in industrial and scientific applications, such as remote control, chemical/biological sensing, optical communication, and spectroscopic and medical instruments.[8] S. Meskers and co-workers reported an infrared PD in which doped poly(2, 4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT/PSS) was used as the active material.[9] More recently, G. Konstantatos and coworkers fabricated NIR-PDs by spin-coating colloidal quantum dots from solution onto gold interdigitated electrodes.[10] The device showed a large photoconductive gain and high detectivity at 1.3 lm. However, 3-dB bandwidth was only about 18 Hz and the working voltage was as high as 40 V. These characteristics strongly restrict their applications in the fields of imaging and communication where high-speed and low-power PDs are desired. Thus, there is a strong need for the development of fast response and low working voltage NIR-PDs while simultaneously maintaining the benefit of low-cost solution process.Here we report an organic near-infrared photodetector using a new low band gap polymer. By utilizing an ester group modified polythieno[3,4-b]thiophene, we have successfully lowered the highest occupied molecular orbital (HOMO) energy level of the low band gap (LBG) polymer, so that it can match the energy level of (6,6)-phenyl C 61 -butyric acid methyl ester (PCBM), and has good solubility and easy processing ability.In this communication, we report a device which has a donoracceptor type energy structure whose operation shows excellent NIR detection capability. Reports on LBG polymers for solar energy conversion have emerged recently. [11][12][13][14][15][16] The preparation of LBG, high mobility, solution-processable polymers is not trivial and requires judicious design.[16] Among several band gap tuning strategies for conjugated polymers, polymerization of fused heterocyclic rings has been known to yield polymers with very low band gaps. [17,18] Polythieno[3,4-b]thiophene (PTT) is one kind of LBG polymers in which the fused thiophene moieties can stabilize the quinoid structure of the backbone, thereby reducing the band gap of the conjugated system. [19,20] Several PTTs without side chains have been reported previously, but the poor solubility makes them difficult to process and limits their use in electro-optical and electronic devices. [21][22][23] Synthesis of alkyl chains substituted thieno [3,4-b]thiophenes monomers have been reported and the resulting polymers exhibit better solubility, but poor oxidative stability. [19] It was found that the HO...

Solution-processed hybrid perovskite photodetectors with high detectivity

“…And a built-in or applied electric field is necessary to separate the electrons and holes to produce an electric current. Various types of semiconductor materials have been applied in photodetectors, such as Si, InGaAs, ZnO, GaN, carbon nanotubes, quantum dots and conjugated polymers [1][2][3][4][5][6][7][8][9][10] . Although certain applications require different features, the key figure-of-merit parameters are responsivity (R), detectivity (D*), noise equivalent power (NEP), linear dynamic range (LDR) and response speed.…”

Narrowband light detection via internal quantum efficiency manipulation of organic photodiodes

“…In fact, the inferred shot noise, which is due to fluctuations in the Poissonian distributed quanta of the current (that is, electrons) obtained from the dark current ffiffiffiffiffiffiffiffiffiffi ffi 2ei d B p ð Þ , where e is the unit charge and B is the detection bandwidth (inversely proportional to the detection time constant), has been shown to differ from the real, measured noise even when the thermal noise is negligible 17,19,51,52 . If we use the shot noise to evaluate the noise equivalent power and the specific detectivity D * , we obtain a larger value for D * , of the order 410 13 Jones.…”

“…NIR photodetectors are important in medical, industrial, communication, scientific and military applications as well as for night-vision imaging and security [14][15][16] . NIR-sensitive photodectectors have previously been demonstrated using inorganic quantum dot sensitization 17,18 , narrow optical-gap donor organic semiconductors within a conventional thin heterojunction structure 14,19,20 , and more recently by harvesting sub-gap charge transfer states (CT) 15,21,22 . Yang et al have reported on the use of CT state absorption to extend the spectral response of an OPD based on a P3HT:PC60BM blend to the NIR 22 .…”

“…In these heterojunctions, careful attention must be given to the optical absorption of the acceptor and donor since both can contribute to the photocurrent through the so-called photo-induced electron (Channel I) and hole transfer (Channel II) processes 25 . While a large range of electron donor materials are available 6,8,15,19 , the choice of electron acceptor is somewhat limited and is dominated by the fullerenes such as PC60BM ( [6,6]-phenyl-C 60 -butyric acid methyl ester) and PC70BM ( [6,6]-phenyl-C 70 -butyric acid methyl ester). 1 A relatively small number of non-fullerene acceptors have been reported but very few exhibit acceptable quantum efficiencies within organic photovoltaic cells 26 .…”

Fluorene-based macromolecular nanostructures and nanomaterials for organic (opto)electronics

“…In the last two decades, various functions of plastic devices have been demonstrated, including polymer light-emitting diodes (PLEDs) [4,5] for commercial flat panel displays and white solid lighting sources, polymer solar cells (PSCs) [6,7], polymer thin-film transistors [8][9][10][11], polymer lasers [12][13][14][15], polymer photodetectors [16][17][18][19], polymer memory for information storage [20][21][22][23][24][25] and others [26][27][28]. In this area, the basic open question pertaining to commercialization is to fabricate low-cost, stable and high-performance thin-film devices.…”