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A series of photomultiplication (PM)-type polymer photodetectors (PPDs) were fabricated with polymer poly(3-hexylthiophene)-[6,6]-phenyl-C71-butyric acid methyl ester (P3HT-PC71BM) (100:1, w/w) as the active layers, the only difference being the self-assembly time of the active layers for adjusting the P3HT molecular arrangement. The grazing incidence X-ray diffraction (GIXRD) results exhibit that P3HT molecular arrangement can be adjusted between face-on and edge-on structures by controlling the self-assembly time. The champion EQE value of PPDs, based on the active layers without the self-assembly process, arrives at 6380% under 610 nm light illumination at -10 V bias, corresponding to the face-on molecular arrangement of P3HT in the active layers. The EQE values of PPDs were markedly decreased to 1600%, along with the self-assembly time up to 12 min, which should be attributed to the variation of absorption and hole transport ability of the active layers induced by the change of P3HT molecular arrangement. This finding provides an effective strategy for improving the performance of PM-type PPDs by adjusting the molecular arrangement, in addition to the enhanced trap-assisted charge-carrier tunneling injection.

Phosphorescent emissive materials in organic light‐emitting diodes (OLEDs) manufactured using evaporation are usually blended with host materials at a concentration of 3–15 wt% to avoid concentration quenching of the luminescence. Here, experimental measurements of hole mobility and photoluminescence are related to the atomic level morphology of films created using atomistic nonequilibrium molecular dynamics simulations mimicking the evaporation process with similar guest concentrations as those used in operational test devices. For blends of fac‐tris[2‐phenylpyridinato‐C2,N]iridium(III) [Ir(ppy)3] in tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA), it is found that clustering of the Ir(ppy)3 (surface of the molecules within ≈0.4 nm) in the simulated films is directly relatable to the experimentally‐measured hole mobility. Films containing 1–10 wt% of Ir(ppy)3 in TCTA have a mobility of up to two orders of magnitude lower (≈10−6 cm2 V−1 s−1) than the neat TCTA film, which is consistent with the Ir(ppy)3 molecules acting as hole traps due to their smaller ionization potential. Comparison of the simulated film morphologies with the measured photoluminescence properties shows that for luminescence quenching to occur, the Ir(ppy)3 molecules have to have their ligands partially overlapping. Thus, the results show that the effect of guest interactions on charge transport and luminescence are markedly different for OLED light‐emitting layers.

A series of polymer photodetectors (PPDs) are fabricated based on P3HT as an electron donor and fullerene-free material DC-IDT2T as an electron acceptor. The only difference among these PPDs is the P3HT:DC-IDT2T doping weight ratios from 2 : 1 to 150 : 1. The PPDs with P3HT:DC-IDT2T (100 : 1, w/w) as the active layers exhibit champion external quantum efficiency (EQE) of 28 000% and 4000% corresponding to 390 nm and 750 nm light illumination at -20 V bias, respectively. The photomultiplication (PM) phenomenon should be attributed to the enhanced hole tunneling injection due to the interfacial band bending, which is induced by the trapped electrons in DC-IDT2T near the Al cathode. The high EQE value in the long wavelength range is due to the effect of DC-IDT2T photon harvesting and exciton dissociation on the interfacial trap-assisted hole tunneling injection. Meanwhile, the PPDs with DC-IDT2T as the electron acceptor exhibit superior stability compared with the PPDs with PC71BM as the electron acceptor.

Charge transport measurement using the Metal-Insulator-Semiconductor Charge Extraction by Linearly Increasing Voltage (MIS-CELIV) technique is a promising method for determining charge mobility in organic semiconductors because of its ability to study electron and hole mobilities independently. However, MIS-CELIV measurements have a number of parameters that can potentially affect the calculated mobility. There are only a few reports on MIS-CELIV being used to determine the charge mobility for materials typically used in organic light-emitting diodes (OLEDs), and the impact of each of the MIS-CELIV experimental parameters on the mobility is presently unknown. We find that the pulse duration, injection time, maximum voltage, offset voltage, and external load resistance have different levels of influence on the calculated mobility. Using the hole transporting OLED host material, tris(4-carbazoyl-9-ylphenyl)amine (TCTA), we show that having an injection time sufficient to fully charge the insulator layer, a pulse duration comparable to the transit time, and an external circuit time constant much smaller than the transit time is required to give a mobility relevant to an OLED. The optimized MIS-CELIV parameters led to the measurement having a similar current density and electric field to that of an operational OLED. Under these conditions, the hole mobility of TCTA was determined to be 2.90 ± 0.07 × 10−4 cm2 V−1 s−1, which is similar to that measured using time-of-flight techniques. Using inappropriate experimental parameters could lead to an underestimation of the mobility by an order of magnitude. Simulations of the MIS-CELIV measurements verified the effect the different parameters played in determining the charge mobility.