Red light detection is vital for numerous applications, including full-color imaging, optical communication, machine vision, etc. However, this development is hindered by a limited choice of small bandgap and narrow bandwidth materials. To solve this problem, the promising strategy of charge collection narrowing has been devised which requires a relatively thick active layer, usually beyond 1.5 μm, to suppress surface-generated carriers thus ensuring the purity of red-light response spectrum, while restricting device frequency bandwidth and introducing extra uncertainties with high throughput deposition methods. Therefore, the realization of thin-film, red-light OPDs would dramatically enhance its potential utility and extend the available range of suitable organic semiconductors. In this work, the selective exciton activation mechanism is applied to a simple planar heterojunction architecture, which enables only specific excitons separated into free charge carriers, while all other excitons are quenched before reaching the donor/acceptor interface. Such a mechanism makes the design of red-light detectivity spectrum even with a considerably thin active layer feasible. By adjusting the ratio of PTB7 in P3HT, an obvious increase of photoresponse is obtained with a peak shift from 645 nm to 745 nm. Moreover, the 90 wt.% PTB7 addition gives high photoresponsivity at 745 nm simultaneously keeping a narrow full-width at-half-maximum of ~50 nm. Highly competitive performance in terms of specific detectivity and linear dynamic range is demonstrated. Therefore, this design concept is intriguing for tunable thin-film filter-less red-light organic photodiodes and also applicable to other spectral windows in the near future.
Vertical organic transistors are an attractive alternative for short channel transistors, in particular, vertical organic permeable base transistors can achieve record-high transition frequencies of up to 40 MHz and drive large current densities of kA cm-2. Here, we design a novel architecture for vertical organic field-effect transistors (VOFETs) with superior electrical performance and simplified low-cost processing. By using electrochemically oxidized aluminum oxide as the charge blocking layer in VOFETs, direct leakage current paths between source and drain can be effectively suppressed, enabling VOFETs with a high on-off ratio and exceptional transconductance. Our anodization technique is easy to be realized and can be readily used on both n-type and p-type organic semiconductor thin films to achieve high-performance VOFETs, opening a new pathway to build, e.g. complementary circuit composed of vertical organic transistors.
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