【Nat.Mater.】运行电压低于3.5V！新一代超低电压电化学有机发光晶体管实现宽达267微米的空间锁定发光
文章标题：Ultralow-voltage electrochemical organic light-emitting transistors with pinned and wide lateral recombination
通讯作者：Tae-Woo Lee
文章概要
引言
有机发光晶体管在可穿戴设备、生物集成系统以及类脑神经形态电子学等领域展现出巨大的应用潜力，它能够将信号处理与视觉反馈完美融合。然而，传统的单活性层有机发光晶体管一直面临着极大的挑战，其内部电荷载流子注入效率低下，导致场效应器件的漏极电压往往需要超过80V，即便在利用电解质的高界面电容降低电压的电化学器件中也需要超过3.5V的电压。此外，由于离子掺杂前沿的动态移动，其发光区域极其狭窄且位置不稳定。这种固有的不稳定性严重限制了可控的实用发光显示，如何在保持低工作电压的同时获得宽且空间锁定的发光复合区域，成为了该领域长期以来的一个核心瓶颈。
Fig. 1: Design of a single-active-layer EOLET.
a, In conventional electrolyte-gated transistor with an LEP channel, electrolyte gating can induce hole transport through the p-channel induced by the electrochemical anion doping of the LEP, but electron injection is absent; therefore, charge carrier recombination is very limited even when LEPs are used as channels. Introducing ITE into the LEP channel facilitates ion transport and forms the cation EDL at the LEP/drain electrode interface. This improves electron injection at even lower voltage than the energy-gap potential (|_V_DS| < |_E_g/e|) and forms a PRZ. b, Schematics of flexible and large-area emission in EOLET. The EDL-induced electron injection allows large-area light emission in the p-channel organic transistor. In addition, the flexible nature of LEP enables mechanical flexibility of EOLET suitable for on-skin applications.
主要实验及结论
研究团队通过在单层发光聚合物通道中引入离子传输增强剂（ITE），成功构筑了漏极侧具有电场双电层结构的单活性层电化学有机发光晶体管。实验通过原子力显微镜、广角X射线衍射和原位紫外可见光谱等手段证实，引入增强剂后发光聚合物的链段构象由卷曲转变为线性纤维结构，显著加速了通道内部的离子传输效率。这种独特的界面设计在偏置电压下于漏极形成了稳定的阳离子电场双电层，从而克服了固有的电子注入势垒。原位拉曼光谱进一步表明，该器件在工作时不仅避免了导致激子淬灭的n型掺杂前沿向前推进，还在漏极附近实现了高效的空穴与电子辐射复合，达成了空间锁定的发光复合区。
Fig. 2: Improving ion transport of LEP channel by ITE incorporation.
a,b, GIXD two-dimensional patterns (a) and one-dimensional diffractograms (b) of pristine MEH-PPV and ITE-incorporated MEH-PPV. c,d, PL spectra of LEP films according to the ITE contents and intensity ratio of I(0–0) and I(0–1) calculated from the PL spectra. e, Schematics of in situ UV–vis spectroscopy setup. f,g, Transition in the absorbance spectrum on voltage application. h, Normalized peak intensity of the absorbance spectrum as a function of doping voltage. i, Cyclic voltammetry curves of pristine and 20% ITE films.
Fig. 3: Operating mechanisms of EOLETs with drain-side EDL.
a, Schematics of EOLET with a lateral gate. b, Operating mechanisms and in situ optical microscopic images of EOLET in operation with constant _V_DS = −2.5 V. Due to stable EDL formation without electrochemical doping, the position of the recombination zone does not change with _V_GS. Scale bar, 100 μm. c, Forward and subsequent backward sweeps from _V_DS = 0 V to −2.5 V with fixed _V_GS = −1.0 V according to the ITE content. EOLET devices with 20% or 30% ITE emitted light at |_V_DS| lower than the energy-gap potential (|_V_DS| < |_E_g/e|) of MEH-PPV. d, Ex situ time-of-flight secondary ion mass spectrometry doping profile of pristine and ITE 20% films. e, In situ Raman spectroscopy measurements of LEP channel on source and drain electrodes for the verification of operating mechanism. During the OFF state, a stable EDL forms without electrochemical doping. During the ON state, electrochemical doping occurs at the source electrode to form p-channels, and radiative recombination occurs at the drain electrode. f, Optical transfer curves of EOLET with constant _V_DS = −2.5 V according to the ITE content. g, EL image of a 4 × 4 EOLET array with line-shaped channel electrodes, showing uniform emission and geometric flexibility. Scale bars, 1 cm (inset). h, EL image of a 10 × 10 EOLET array with the surrounding electrode channel, confirming large-area integration and high device density. Both array formats highlight the universality of the solution-based fabrication process. Scale bars, 1 cm (inset).
得益于这一创新机制，该器件展示出前所未有的优异性能，在仅为3.5V的超低漏极电压下实现了宽达267微米的发光复合区，其最大亮度达到了每平方米826坎德拉。同时，器件的电学开关比超过了万倍，且在连续偏置应力下表现出大幅提升的运行稳定性，发光半衰期表现优异。研究人员不仅利用这种溶液法工艺成功制备出了具有高均匀性的100像素大面积集成器件阵列，还充分利用发光聚合物和固体电解质的柔性特质，实现了在频繁弯曲和扭曲状态下依然能够稳定高亮发光的柔性大面积显示器件，证明了该材料体系优异的力学形态适应性。
Fig. 4: Flexible and large-area EOLETs.
a, Photographs of large-area EOLET in ON states (_V_GS = _V_DS = −3.5 V). b, Schematics of the operating mechanism of large-area EOLET. c, RZW depending on _V_DS and _V_GS, indicating the enhancement of electron injection and hole transport, respectively. d, Comparison of EOLET performance with reported single-active-layer OLETs. e, Photographs of flexible EOLET being bent and twisted, and of different patterns and colours. f, Schematic of the SAND system: flexible touch sensor, flexible ring oscillator, flexible EOLET and two 1.5-V batteries. This system has an intrinsic threshold for response to weak stimuli (for example, touch by a blunt object, brief touch by a sharp object), as do biological nerves. g, Visual spike responses of SAND versus simulation duration. Stimuli are encoded to spike signals and induce visual responses due to the synaptic plasticity of EOLET. h, Maximum _I_Ph of SAND versus stimulation duration. i, Retentive _I_Ph at 30 s after stimulation. In g–i, the grey dashed lines represent the noise levels.
总结及展望
这项工作成功开辟了有机发光晶体管设计的新范式。通过精细调控发光聚合物通道内的离子传输，不仅彻底打破了工作电压和发光区域稳定性之间的固有权衡，更为开发低功耗、高集成度的可穿戴智能视觉反馈电子系统奠定了坚实的基础。作为概念验证，团队还将其与柔性触觉传感器及环形振荡器集成，构筑出了仅需两节普通干电池驱动的独立类脑感知柔性可穿戴系统，这预示着该技术未来在医疗健康监测、智能仿生皮肤以及人机交互显示等前沿领域具有广阔的产业化应用前景。