Realizing photomultiplication-type organic photodetectors based on C ₆₀ -doped bulk heterojunction structure at low bias

Abstract

Photomultiplication (PM) structure has been widely employed to improve the optoelectronic performance of organic photodetectors (OPDs). However, most PM-type OPDs require a high negative operating voltage or complex fabrication. For obtaining high-efficiency OPDs with low voltage and easy process, here the bulk heterojunction (BHJ) structure of high exciton dissociation efficiency combined with the method of trap-assisted PM are applied to the OPDs. In this paper, we investigate the operating mechanism of OPDs based on poly(3-hexylthiophene) (P3HT): (phenyl-C61butyric-acid-methyl-ester) (PC 61 BM), and poly-{ [4,8-bis[(2-ethylhexyl) [3,4-b]thiophene-4,6-diyl]} (PBDT-TT-F):PC 61 BM doped with C 60 as active layer. Furthermore, the influence of C 60 concentration on the optoelectronic performances is also discussed. With 1.6 wt.% C 60 added, the P3HT:PC 61 BM:C 60 OPD exhibits a 327.5% external quantum efficiency, a 1.21 A•W −1 responsivity, and a 4.22 × 10 12 Jones normalized detectivity at −1 V under 460 nm (0.21 mW•cm −2 ) illumination. The experimental results show that the effective electron traps can be formed by doping a small weight of C 60 into BHJ active layer. Thus the PM-type OPDs can be realized, which benefits from the cathode hole tunneling injection assisted by the trapped electrons in C 60 near the Al side. The efficiency of PM is related to the C 60 concentration. The present study provides theoretical basis and method for the design of highly sensitive OPDs with low operating voltage and facile fabrication.

A new method to enhance organic photodetectors active layer trap doping by blending doping

“…When the doping concentration is increased to 1.0 wt%, the maximum value is 5.83×10 17 cm −3 . The reason for the decrease in the trap concentration is that when the doping concentration is more than 1.0 wt%, the impurities will aggregate, which reduces the doping efficiency and causes the decrease of trap concentration [9,23]. In order to solve the problem of impurities aggregation, a blending doping method is proposed in this paper and the second group of blending doping is studied.…”

“…The blending doping G is significantly thinner than the single-doped E hole barrier. The thinning of the barrier width indicates that the charge accumulation on both sides of the active layer/Al electrode interface increases, and thereby the trap concentration of the active layer increases [16,22,23].…”

Inverted ternary OPD based on PEIE

“…This research group has conducted a lot of research on this, mainly focusing on doping electron traps to induce hole tunneling to improve the external quantum efficiency of the device. For example, the active layer P3HT: PC 61 BM is doped with C 60 as an electron trap, so that the device can achieve an external quantum efficiency as high as 327.5 % under -1V bias voltage and 460nm illumination [8]. Doping C 60 into the active layer PBDT-TT-F:PC 61 BM, the device achieves an external quantum efficiency as high as 739.8% under a bias of -3V and 630nm illumination [9].…”

Accurate capacitance–voltage characterization of organic thin films with current injection*

“…With the advantage of being sensitive to the number of carriers within device and their spatial distribution simultaneously, the capacitance technique has been widely adopted in the study of organic thin films (including organic photovoltaics, organic light-emitting diodes, etc.) to probe device properties such as carrier mobility, [1][2][3][4][5][6][7][8][9][10][11] doping density, [12,16] deep trap states, [17][18][19][20][21] and exciton behavior. [22,23] However, rather than the direct obtainment of capacitance, the magnitude and phase of impedance are firstly measured with an LCR meter, subsequently the capacitance of device is calculated according to the circuit model selected.…”