Dynamic Characterization of Green-Sensitive Organic Photodetectors Using Nonfullerene Small Molecules: Frequency Response Based on the Molecular Structure

Abstract

The dynamic characterization of two green-sensitive organic photodetectors (OPDs) using nonfullerene small molecules is investigated by analyzing the electrical parameters based on the experimental results and the simulated data. The two OPDs comprise N,N-dimethyl quinacridone (DMQA) as the common donor and dibutyl-substituted dicyanovinyl terthiophene (DCV3T) or boron-subphthalocyanine chloride (SubPc) as respective acceptors. At the applied voltage of −5 V, the device composed of DMQA/SubPc shows a higher frequency response at 148.3 kHz, by 55 kHz higher than the device based on DMQA/DCV3T. The impedance spectroscopy results indicate that the former device exhibits the low resistance due to the high mobility and the low capacitance linked to the dielectric constant. According to the molecular quantum calculation, the linear structure of DCV3T may promote packing of adjacent molecules in the linear direction, resulting in a high polarizability. In contrast, the fused structure of SubPc leads to a decrease in reorganization energy, and its conical shape tends to counterbalance the net dipole at the axial position in the dimer packing configuration owing to the symmetry of the three-branched units in the molecular periphery, which are related to the high carrier mobility and the low dielectric constant. The OPD comprising SubPc, with the dynamic response surpassing the commercialization level of 100 kHz, also exhibits good static performance with an external quantum efficiency of 60.1% at the wavelength of 540 nm, which can be an interesting candidate for potential applications as image sensors.

Solution-processed semiconductors for next-generation photodetectors

“…3 Organic semiconductors are arguably the most optoelectronically adaptable of these classes of materials by virtue of their almost limitless molecular diversity. In particular, they have been shown significant potential for achieving color discrimination through molecular 4 and device architecture 5 tuning, or utilization of both strategies in combination. 6 Low noise, broadband visible-near IR light detection have also been reported.…”

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.…”

“…Small-molecule semiconductors with narrowband absorption properties have played a key role in the development of organic narrowband photodetectors (see section 5.1). A significant number of them are drawn or derived from compounds originally developed as industrial colourants, laser dyes, or fluorescent probese.g., blue-absorbing coumarins [22,[44][45][46][47], green-absorbing rhodamines [44,45,[48][49][50][51] and quinacridones [11,47,[52][53][54][55][56][57][58][59][60][61][62][63], green-and red-absorbing phthalocyanine metal/metalloid complexes and derivatives [11, 44, 45, 47, 49, 54-56, 58, 61, 64-70], and green-, red-, and NIR-absorbing squaraines [23,[71][72][73] ( figure 4(b)). It is noteworthy that some narrowband-absorbing small molecules are able to form aggregates (Jand H-aggregates) featuring particularly narrow and intense absorption bands (FWHM α <20 nm, α up to 10 6 cm −1 ), a property that is very attractive for narrowband photodetection [24,[74][75][76][77][78][79].…”

“…Their outstanding electron-accepting properties in BHJs and PHJs (in combination with polymeric and smallmolecule donors alike) have led to their widespread use in all types of narrowband photodetector configurations [19,30,31,[80][81][82][83][84][85]. However, their broad absorption tail through the visible has been problematic in some configurations (see section 6.3), and this has recently prompted the development of alternative small-molecule acceptors with narrowband absorption [11,[57][58][59][60][61] or with diverse onsets [42,[86][87][88].…”

“…Organic green-selective photodetectors have achieved the highest quantum efficiency (>50%) in primaryphotocurrent mode through the NBA approach [11, 57-59, 61, 120, 128, 129, 133]. A large number of these works rely on green-absorbing quinacridone dye derivatives (used as donors) [11,[57][58][59]61], leading to a maximum EQE p of 67.6% in combination with green-absorbing DCV3T (used as an acceptor) ( figure 7(b)) [57]. 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)).…”