Device performance enhancement via a Si-rich silicon oxynitride buffer layer for the organic photodetecting device

Abstract

An advanced organic photodetector (OPD) with a butter layer of Si-rich silicon oxynitride (SiO x N y ) was fabricated. The detector structure is as follows: Indium tin oxide (ITO) coated glass substrate/ SiO x N y (10 nm)/naphthalene-based donor:C60(1:1)/ITO. Values of x and y in SiO x N y were carefully controlled and the detector performances such as dark current and thermal stability were investigated. When the values of x and y are 0.16 and 0.66, the detector illustrates low dark current as well as excellent thermal stability. In the OPD, silicon oxynitride layer works as electron barrier under reverse bias, leading to the decrease of dark current and increase of detectivity. Since the band gap of silicon oxynitride unlike conventional buffer layers can also be controlled by adjusting x and y values, it can be adapted into various photodiode applications.Organic photodetectors (OPDs) have been widely used in practical applications such as photo-sensors, chemical sensors 1-6 , X-ray detectors 7 , and image sensors [8][9][10][11] . Among the applications, image sensors, which have been considered of replacing conventional silicon-based image sensors 4, 10 , have attracted research interest from industries and there has been considerable effort to improve the device performances of them such as the spectral response, external quantum efficiency (EQE), dark current (DC), and sensitivity. Among these, the External quantum efficiency (EQE), DC, and thermal stability are the key factors to evaluate the performance of OPDs. EQE is coupled to the efficiency and signal-to-noise ratio (SNR) of the devices. Low DC stabilizes the signal of the devices, leading to high SNR. Because organic materials in OPDs are exposed to high temperature process such as post-annealing at 180 °C, passivation step, top layer planarization, and microlens forming process, they should be thermally stable without performance degradation.Decreasing DC and enhancing thermal stability have been generally improved by introducing new buffer layers 12 such as MoO x 13 , WO x 14 , and VO x 15 . However, MoO x is susceptible to the loss of oxygen during evaporation which can result in the change of stoichiometry and electronic energy levels 16 . Since various active materials are also used in fabricating OPDs, the band structure of a buffer layer should be aligned to HOMO and LUMO levels of bulk heterojuction (BHJ) films. Conventional buffer layers such as MoO x are very difficult to change their band structure, i.e. their HOMO and LUMO levels do not change without regard to neighboring active materials. Therefore, new buffer layers with thermal stability and easily adjustable band structure have been required.As one of good candidates for new buffer layers, silicon oxynitride (SiO x N y ) film has been well received because its band structure is able to be freely controlled by adjusting the x and y. Moreover, it is thermally stable at high temperature process and is also chemically inert enough to be used in electronic devices 17 such as thin-film tr...

Efficiency and spectral performance of narrowband organic and perovskite photodetectors: a cross-sectional review

“…The reasons for this are manifold: (a) the ease and attractiveness of the NBA approach to achieve narrowband photodetection (section 5.1); (b) the later development of CCN and microcavity approaches; (c) the limited edge of the input-filtered strategy (in view of its overlap with conventional narrowband photodetection, with which it shares similar challenges). In primary photocurrent mode, the NBA strategy has led to the highest EQE figures of all narrowband approaches (up to 60%-80%), as exemplified by figure 6(a) [46,57,58,61,70,95,128,129]. This can be rationalised in terms of its straightforward operation, which does not require filtering and/or the introduction of deliberate loss mechanisms.…”

“…Chloroboron subphthalocyanine (SubPc) is another small molecule that has delivered high phototransduction efficiency in a number of works, giving an EQE p of 62.6% in combination with DCV3T [58], and 60.1% in combination with quinacridone [58,61] (figure 7(b)). Newly synthesised small-molecule donors featuring a D-A structure approaching the cyanine limit have also yielded EQE values in the ≈50%-70% range in combination with fullerenes ( figure 7(b)) [120,126,128,129]. Finally, Li et al demonstrated the potential of a singlecomponent squaraine photoactive layer, achieving an EQE p as high as 66% [72].…”

“…A considerable number of NBA-type devices feature a FWHM EQE greater than 100 nm. A recurrent feature of many of them is the use of fullerenes, which generally broaden the spectral width and/or reduce the spectral rejection ratio (e.g., with respect to the blue, see figure 7(b)) [120,125,126,128,129]. A number of fullerene-free strategies have thus been considered to overcome this challenge and achieve FWHM EQE values around or below 100 nm.…”

Synthesis of a Novel Polyethoxysilsesquiazane and Thermal Conversion into Ternary Silicon Oxynitride Ceramics with Enhanced Thermal Stability

“…On the other hand, nonstoichiometric silicon oxynitride (SiO x N y ) films can be fabricated by plasma enhanced chemical vapour deposition (PECVD) [12,13,14,15,16,17,18,19]. In addition to better dielectric properties, SiO x N y films show excellent optical properties.…”

“…The optical losses in SiO x N y films are significantly low, and the refractive index of the films can be controlled in the wide range from 1.45 for SiO 2 to 2.0 for Si 3 N 4 [12], which can offer potential applications, such as antireflective coatings [13] and waveguide layers [14,15,16]. Moreover, SiO x N y films exhibit sufficient thermal and chemical stabilities, and can thus be expected to be used for electronic devices [13,17] and buffer layers [18,19]. …”