Charge Transport Behavior and Ultrasensitive Photoresponse Performance of Exfoliated F₁₆CuPc Nanoflakes

Abstract

Air‐stable, photosensitive copper hexadecafluorophthalocyanine (F16CuPc) is a promising n‐type semiconductor for organic electronics and optoelectronics. However, the performance of F16CuPc‐based devices is significantly limited by the poor crystallinity of thin films. Here, the charge transport and electrical contact behavior of F16CuPc nanoflakes, mechanically exfoliated from needle‐like bulk single crystals, are probed by analyzing the temperature‐dependent carrier mobility and conductance, where the multiple‐trap/release‐ and band‐like transport mechanism govern the charge transport at different temperature ranges and carrier densities. F16CuPc nanoflake‐based field effect transistors (FETs) exhibit high on‐state current and ON/OFF ratio, one‐order magnitude higher than those of reported F16CuPc nanowires, thin films, and nanoribbons. Besides, F16CuPc nanoflake‐based phototransistors exhibit attractive photoresponse performance in the spectral range of 300–750 nm even at quite low operating source–drain voltage (1 V), with maximum photoresponsivity of 19 A W−1, detectivity of 8 × 1012 Jones, and fast response speed of 36 ms, which is attributed to the single‐crystalline characteristic of nanoflakes, and the resultant efficiently exciton diffusion and charge transport. The work demonstrates that 2D organic nanoflakes with single‐crystalline feature will be promising candidates for flexible electronic and optoelectronic devices.

Lowering the Contact Barriers of 2D Organic F16CuPc Field‐Effect Transistors by Introducing Van der Waals Contacts

“…The electron mobility of 1T‐TaSe 2 ‐contacted device at room temperature is determined to be 0.28 cm 2 V −1 s −1 , larger than that of evaporated Au‐contacted device (0.21 cm 2 V −1 s −1 ). [ 41 ] We then focus on the output characterizations of these two devices. The output curves of evaporated Au‐contacted OFET at room temperature show a nonlinear character as depicted in Figure 2f, while those of 1T‐TaSe 2 ‐contacted devices exhibit obvious linearity with V ds ranging from −5 to 5 V, as presented in Figure 2e, indicating decreased barrier at the contact interface.…”

“…[ 9,30,51 ] Compared with evaporated Au contact, 1T‐TaSe 2 contact enables the efficient charge transport within F 16 CuPc for that the superior band‐like charge transport regime is broaden. [ 41 ] The µ – T relation fitted by MTR mechanism can be expressed as Equation () …”

“…It is observed that both devices exhibit high sensitivity to light even at quite a low source–drain voltage of 1 V, consistent with our previous work, where the optoelectronic performance of F 16 CuPc‐based OPT has been greatly improved by using 2D single‐crystalline F 16 CuPc nanoflake as the channel. [ 41 ] To further explore the optoelectronic performance of 1T‐TaSe 2 ‐contacted device, responsivity ( R ) and specific detectivity ( D *, assuming that the noise of dark current is the major noise source) were evaluated. Responsivity and specific detectivity are defined by Equations () and (), respectively where the I light and I dark represent the source–drain currents under illumination and dark conditions, respectively, P inc is the power density of incident light and A is the effective illumination area.…”

“…Most visible‐light OPTs operate on relatively high voltages to deliver high R and D *, whereas F 16 CuPc nanoflake‐based OPT with vdW contact shows superior performance to most visible‐light OPTs even at a very low operating voltage ( V ds = 1 V), which offers new opportunities for emerging photodectectors. [ 41,57–67 ]…”

Nanowire Junction Induced High Threshold Voltage in Poly(3‐hexylthiophene) Mesoscale Crystalline Thin‐Film Transistors with Significantly Enhanced Mobility

“…In organic semiconductors, the multiple trap and release (MTR) model is widely used to explain the transport characteristics of carriers . The model considers that the carriers are bound by the local states in the forbidden band of semiconductor when they transport in the extended state.…”