High Efficiency and Uniform Emission in Micropixelated Inorganic/Organic Hybrid Vertical Light-Emitting Transistors and Displays

Vertical light-emitting transistors (VLETs) fabricated by integrating organic vertical transistors and organic light-emitting diodes (OLEDs) have been proposed as a prospective building block for display technologies. However, organic vertical transistors normally have non-ohmic injection and a low-mobility channel, resulting in low VLET performance compared to the pristine OLED. The difficulty of fine patterning the source electrode and organic layer in a stacked VLET geometry has also been a technical issue limiting industrial applications. This paper reports on a simple approach to realize a high-performance, miniaturized VLET by using a highly conductive, well-designed inorganic transistor. Here, we investigate the ZnO transistor configured with an insulator-encapsulated source electrode to confine the current pathway in the VLET, which can be easily fabricated and integrated with various solution-processed or vacuum-sublimed inverted OLEDs (IOLEDs). This ZnO transistor exhibits ohmic contact and a high electron mobility of >10 cm2/(V s) that enables effective electron injection and lateral transport in the VLET, forming a millimeter-scale density gradient (channel depth) for strong surface emission. Furthermore, the high mobility of ZnO facilitates the design of a simple source pattern with a large aperture ratio on the ZnO area to control the current density and distribution and thus the VLET output. From a systematic study of the source design, we show that the ZnO transistor can be optimized to achieve homogeneously high conductivity in the ON state and yield the best VLET performance with maximum emission intensity and efficiency close to those of the IOLED, while the emission can be spatially uniform and precisely defined by the ZnO pattern. Finally, we implement a micropixelated VLET-based active matrix panel to demonstrate the prospect of high-resolution display applications.垂直发光晶体管（Vertical Light-Emitting Transistors，VLETs）是将有机垂直晶体管与有机发光二极管（Organic Light-Emitting Diodes，OLEDs）集成制备得到的器件，已被提出作为显示技术领域极具应用前景的构建单元。然而，有机垂直晶体管通常存在非欧姆注入与低迁移率沟道问题，导致VLET的性能远不及原始OLED器件。此外，在堆叠式VLET结构中对源电极与有机层进行精细图案化的难题，也是制约其工业化应用的技术瓶颈之一。本文提出了一种简便方案，通过使用高导电性、优化设计的无机晶体管来制备高性能微型化VLET。本研究中，我们设计了带有绝缘封装源电极的ZnO晶体管，以限制VLET内的电流通路，该器件制备简便，可与各类溶液加工型或真空蒸镀型倒置有机发光二极管（Inverted OLEDs，IOLEDs）集成。该ZnO晶体管具备欧姆接触特性，电子迁移率高于10 cm²/(V·s)，可在VLET中实现高效的电子注入与横向输运，从而形成毫米级密度梯度（沟道深度）以实现强表面发射。此外，ZnO的高迁移率特性使得我们可以在ZnO区域设计简单的源极图案，实现高开口率，从而精准调控电流密度与分布，进而优化VLET的输出性能。通过对源极设计的系统性研究，我们证实可通过优化ZnO晶体管，使其在导通状态下实现均匀的高导电性，从而使VLET获得最优性能：其最大发射强度与效率可接近IOLED的水平，且发射区域可通过ZnO图案实现空间均匀分布与精准定义。最后，我们制备了基于微像素化VLET的有源矩阵面板，展示了其在高分辨率显示应用中的应用前景。