## 3 Organic Light Emitting Field Effect Transistors (OLEFETs)  
The emergence of organic light-emitting field-effect transistors (OLEFETs) has sparked renewed interest in organic optoelectronics [42; 43]. OLEFETs utilize organic semiconductors capable of achieving supramolecular organization, facilitating both charge carrier transport and electroluminescence [44]. These multifunctional devices combine the current modulation capabilities of a transistor with light emission, making them appealing for both fundamental research and practical applications. OLEFETs serve as excellent platforms for investigating physical processes such as charge carrier injection, transport, and electroluminescence (EL) in organic semiconductors. Unlike organic light-emitting diodes (OLEDs), which typically feature a vertically stacked geometry, the planar geometry of OLEFETs provides direct access to optical probes for imaging electroluminescence. Consequently, OLEFETs hold promise for the development of highly integrated organic optoelectronic devices, including active matrix full-color electroluminescent displays. Fur thermore, their advancement could lead to the realization of electrically driven organic lasers with tunability across the visible spectrum [45]. An OLED typically consists of a vertical stack of organic layers situated between two electrodes--the cathode and the anode. The layers within this stack serve specific functions: the hole-injection layer (HIL) facilitates the injection of holes from the anode, the hole-transport layer (HTL) transports holes to the emissive layer (EML), where light emission occurs, and the electron-transport layer (ETL) manages the transport of electrons from the cathode. The light emission in OLEDs is a result of electron-hole recombination within the EML, with charge transport mainly governed by tunneling through adjacent organic layers. In contrast, OLEFETs feature a different architecture, characterized by a three-terminal setup that includes a source, drain, and gate terminal. The active organic layer in an OLEFET is separated from the gate electrode by a dielectric layer, and the charge transport mechanism is primarily lateral and field-effect driven. In OLEFETs, the gate voltage modulates the charge carrier density in the channel, influencing the device's electrical characteristics and light emission. Unlike OLEDs, which rely on vertical charge transport and layer-specific functions, OLEFETs leverage lateral field-effect modulation for both switching and light emission, making them distinct in their operational principles and design considerations (Figure 4) [46]. OLEFETs offer several advantages over OLEDs. They can be fabricated in various shapes and geometries on different substrates, require fewer layers compared to OLEDs, and are less sensitive to defects like pinholes and shorts due to the dielectric layer. Additionally, OLEFETs exhibit higher brightness with both top and bottom emission and have the potential for reduced power consumption since they are voltage-driven. This characteristic makes them easier to integrate into complex device architectures and compatible with commercial integrated circuits (ICs), potentially lowering fabrication costs and improving manufacturing yields. Furthermore, OLEFETs can be driven by various types of thin-film transistors (TFTs), including less advanced organic TFTs (OTFTs), which makes them particularly suitable for flexible and wearable electronics. In comparison, OLEDs are characterized by a vertical stacking of organic layers that each serve specific functions such as hole and electron injection, transportation, and light emission. This architecture requires more layers and is generally more sensitive to defects. On the other hand, OLEFETs benefit from a planar structure that simplifies the pixel architecture and enables the intrinsic capacitance of the transistor to perform the pixel memory function. This simplification also contributes to an aperture ratio of approximately 80%, which readily meets display requirements.