Abstract
Polarized emissive media are crucial for various applications in display, lighting and optical communication. An attractive research direction is to develop intrinsically white organic polarized emissive semiconductors as ideal candidates for miniaturized polarized light-emitting devices; however, it has been a considerable challenge to achieve polarized white-light emission due to the lack of suitable materials and effective preparation methods. Here we overcome this bottleneck by realizing white organic polarized emissive semiconductor single crystals (WOPESSCs). We employ a bimolecular doping method based on using highly polarized, blue-emitting 2,6-diphenylanthracene as the host single crystal, and controlling energy and polarization transfer with green- and red-emitting guests. The fabricated WOPESSCs achieve a photoluminescence quantum yield of 38.3% and a mobility of 4.9 cm2 V–1 s–1. The emitted light exhibits a degree of polarization as high as 0.96 with Commission Internationale de l’Eclairage coordinates of (0.3258, 0.3396). We also demonstrate the tunable emission properties of WOPESSCs from blue–white to yellow–white light by adjusting polarization angles, and three-primary-colour optical imaging with a wide colour gamut that covers 112% of the National Television System Committee standard. Furthermore, we fabricate highly polarized microscale WOPESSCs light-emitting diodes and light-emitting transistors, achieving high-quality white-light emission and wide-range colour tunability enabled by gate voltage-driven energy transfer processes. We believe these findings pave the way for manufacturing white and multicolour polarized emissive semiconductors and microscale light-emitting devices, promising diverse applications across various fields.
Main
Polarization is one of the fundamental properties of light, along with wavelength and intensity. Polarization imparts spatial information to light, enabling the control and use of its polarization state for high-dimensional information transmission and detection1,2,3. Polarized light sources are crucial for applications in various fields, including biological imaging, anti-glare displays, machine vision, optical communications, anti-counterfeiting and security4,5,6. Polarized light emission is normally achieved by combining an unpolarized light source with additional polarizers or by integrating it with micro- or nanostructures7,8. For instance, linearly polarized light can be obtained by passing unpolarized light through a linear polarizer. Similarly, circularly polarized light can be directly obtained by continuously passing unpolarized light through a linear polarizer and a quarter-wave plate9,10. These technologies are relatively mature but pose challenges for applications in miniaturized devices and circuits due to their complex manufacturing processes and relatively large size. An emerging strategy to overcome these challenges is the development of intrinsically polarized emissive materials such as organic semiconductor single crystals8,11. These materials offer unique advantages, including intrinsic structural anisotropy, inherent asymmetry of transition dipole moment (TDM), molecular design flexibility and superior optoelectronic properties12,13,14,15.
So far, important advances have been made in organic polarized emissive semiconductor single crystals with specific emission wavelengths8,11. However, it remains challenging to achieve a monolithic organic semiconductor that emits uniform white polarized light. Synthesizing efficient single-molecule white-emitting materials in the solid-state is inherently challenging, primarily due to the constraints imposed by Kasha’s rule16,17, which typically causes fluorescent materials to emit monochromatic light from their lowest vibrational state. Furthermore, the stereochemical features of most white-emitting materials make it difficult to grow high-quality single crystals. Alternatively, constructing a molecular doping system that features several emissive materials with complementary colours is a promising approach for white-light emission; however, the mismatch in sizes and structures of most molecules often leads to their formation as thin films18,19, resulting in disordered TDMs, thus hindering intrinsically polarized emission. Beyond realizing white polarized emission, it is important to combine it with excellent optoelectronic performance such as high photoluminescence quantum yield (PLQY) and charge carrier mobility. This is crucial for developing efficient and power-effective miniaturized light-emitting devices for a range of advanced applications in solid-state lighting, full-colour displays, optical communications and machine vision.
In this study we present a bimolecular doping method to realize intrinsically white organic polarized emissive semiconductor single crystals (WOPESSCs). Our strategy uses a 2,6-diphenylanthracene (DPA) single crystal as the host, which was chosen for its superior optoelectronic properties. We combine DPA with green-emitting tetracene (Tc) and red-emitting pentacene (Pen) due to their similar molecular structures, sizes and suitable energy levels. Such compatibility facilitates the formation of high-quality bimolecular-doped single crystals, as well as the establishment of efficient energy and polarization transfer pathways between the host and the guests, which enables intrinsically white polarized emission. Our WOPESSCs exhibit remarkable optoelectronic properties, including a high degree of polarization (DOP) of 0.69–0.96 across the visible spectral range, a PLQY of 38.3%, a mobility of 4.9 cm2 V–1 s–1, and Commission Internationale de l’Eclairage (CIE) coordinates of (0.3258, 0.3396). By adjusting the polarization angles, we achieve tunable emissions ranging from blue–white light to yellow–white light. Using mask-free fabrication techniques, we also successfully manufacture microscale organic polarized light-emitting diodes (OPLEDs) with a high DOP of 0.91. Moreover, the electroluminescent spectra of WOPESSCs light-emitting transistors could be modulated over a wide range, shifting from (0.5691, 0.3554) to (0.2968, 0.2233) in CIE coordinates by tuning the applied gate voltage. Such versatility makes WOPESSCs suitable for various application scenarios. Our findings demonstrate an effective strategy for designing polarized emissive semiconductors and miniaturized light-emitting devices with broad application prospects.
Results
Roadmap towards polarized white-light emission
Molecular doping is a powerful strategy for modulating the electrical and optical properties of organic semiconductors20,21. Here we present the fabrication of WOPESSCs using bimolecular and lattice-induced ordered doping. To prepare WOPESSCs, we deliberately select the highly polarized blue-emitting DPA single crystal (Fig. 1a)—which has a DOP of 0.97—as the host22. Green-emitting Tc and red-emitting Pen are selected as the guests. These selections were made on the basis of the following considerations. First, the guests and host are fused-ring conjugated compounds with similar molecular sizes (Fig. 1b and Supplementary Note 1)23,24,25, molecular structures, and electron density distributions (Fig. 1c)26. As depicted in Fig. 1b, the size of Pen and Tc molecules is slightly smaller than that of DPA in all three dimensions. This size difference facilitates the fabrication of molecularly doped single crystals. Second, the overlap between the fluorescence spectrum of DPA single crystals and the absorption spectrum of the guests ensures the efficient energy transfer from host to guest (Supplementary Fig. 1). Third, the emission spectra of the host and guests exhibit suitable characteristics, encompassing three primary colours (Supplementary Fig. 2). This indicates the potential to fabricate WOPESSCs by fine-tuning the doping concentration (Fig. 1d). The long-range ordered molecular stacking of host single crystal and lattice-induced molecular doping are critical prerequisites for achieving the alignment of the TDMs of the host and guests, thereby enabling intrinsically polarized emission of WOPESSCs. We therefore believe that efficient energy and polarization transfer can occur between the host and guests (Fig. 1e).
Fig. 1: Molecular doping design concepts for realizing WOPESSCs.
a, Molecular stacking diagram of DPA single crystals in the bc crystal plane. b, The size of the host or guest molecule is defined as the size of the smallest box that can frame the Van der Waals surface of the molecule. Blue, DPA; red, Pen; green, Tc. These coloured values represent the size of the box’s corresponding border, reflecting the size of the molecule. c, The electron density of DPA (blue), Pen (red) and Tc (green). d, Schematic diagram of a WOPESSC. e, Schematic diagram of energy and polarization transfer between host and guest molecules in a WOPESSC.
Optical characterization of WOPESSCs
The selection of an appropriate doping concentration is vital to achieving white-light emission. Various doping concentrations are optimized for white-light emission. The specific doping concentration used for preparing WOPESSCs is described in Methods. For instance, when the mass ratio of Tc 3%:Pen 0.5% is set to 4:1, double-doped single crystals that exhibit close to white-light emission are produced. Fluorescence image and spectra (Supplementary Fig. 3) of a double-doped single crystal (Fig. 2a) and confocal fluorescence images (Fig. 2b) together demonstrate the uniform doping of Pen and Tc. As confirmed by an optical microscopy image (Supplementary Fig. 4) and fluorescence spectra (Fig. 2c), WOPESSCs were successfully prepared at the optimal doping concentration (Tc 3%:Pen 0.5% = 3:1). Regular micrographs displaying typical birefringence features (Supplementary Fig. 5) confirm that the prepared WOPESSCs are high-quality single crystals. Furthermore, X-ray diffraction (XRD) analysis (Supplementary Fig. 6) demonstrates that the structure of WOPESSCs is identical to that of DPA single crystals (CCDC no. 1044209)27,28,29, indicating that the molecular stacking of the host remains unaffected after bimolecular doping.
Fig. 2: Fluorescent properties of double-doped single crystals and WOPESSCs.
a, Bright-field image of a double-doped single crystal. Scale bar, 25 μm. b, Confocal fluorescence images collected at different focal planes (interplane distance = 150 nm). Scale bar, 25 μm. c, Fluorescence spectra of a WOPESSC. d, TCSPC decay curves and corresponding fitting results of DPA single crystals and WOPESSCs at an emission wavelength of 472 nm. e, A photograph of WOPESSCs grown on a 0.9 × 0.9 cm2 silicon wafer under ultraviolet light. f, CIE coordinates of 29 WOPESSCs. The inset is a fluorescence image of WOPESSCs.
We investigated the decay lifetimes of DPA single crystals and WOPESSCs using a time-correlated single-photon counting (TCSPC) system. The TCSPC decay curves at an emission wavelength of 472 nm for DPA single crystals and WOPESSCs, along with the corresponding fitting results, are presented in Fig. 2d. The calculated decay lifetime (τ0) of DPA single crystals is 8.56 ns. By contrast, the decay lifetime (τd) of WOPESSCs decreases to 2.94 ns, indicating the occurrence of effective energy transfer within the WOPESSCs with an energy transfer efficiency of 66% (ref. 30). The characterization of the WOPESSCs—including fluorescence images, fluorescence spectra and energy transfer efficiency—confirms that effective energy transfer between host and guests has occurred. Efficient energy transfer between host and guests, as well as the dispersion of guests in the WOPESSCs, contribute to the high fluorescence efficiency. Ultimately, the prepared WOPESSCs exhibit a PLQY of 38.3%. As shown in Fig. 2e, a large quantity of WOPESSCs is grown on a 0.9 × 0.9 cm2 silicon wafer, and the uniform luminescence of each crystal is displayed in the inset of Fig. 2f. Photoluminescence spectra of 29 WOPESSCs are collected, and the calculated CIE coordinates (Fig. 2f) demonstrate the highly uniform and controllable white-light emission of WOPESSCs.
Polarized fluorescence properties
It is necessary to determine the crystal axes to investigate the polarized emission properties. On the basis of the XRD data (Supplementary Fig. 6), the growth model of WOPESSCs reveals a bc crystal plane parallel to the substrate. The orientation of in-plane crystal axis can therefore be determined by analysing the angle formed by the natural growth edges of WOPESSCs22,31. The polarized fluorescence and electroluminescence spectra measurements are conducted with the initial polarization degree of the polarizer aligned parallel to the c-axis. Figure 3a and Supplementary Fig. 7 show the fluorescence intensity dependence on the polarization angle, indicating the remarkably highly polarized fluorescence properties of WOPESSCs. The polarized fluorescence spectra are monitored at three major peaks: ~450 nm, ~500 nm and ~610 nm for DPA, Tc and Pen, respectively. The DOP is calculated using the formula (Imax – Imin)/(Imax + Imin), where Imax and Imin represent the maximum and minimum values of the emission intensity at the peak wavelength, respectively32,33. The DOP values are approximately 0.96, 0.71 and 0.69 for 450 nm, 500 nm and 610 nm, respectively (Fig. 3b). The DOP values of four WOPESSCs (Supplementary Fig. 8) showed minimal differences (Fig. 3c), highlighting the intrinsically polarized emission characteristics of WOPESSCs. We speculate that the alignment of the TDMs of the host and guest molecules, induced by the lattice-induced ordered doping in WOPESSCs, plays a crucial role in polarization transfer (Supplementary Fig. 9). The dominant polarized emission direction of the host and guest molecules is along the c-axis, suggesting the polarization transfer from the host to the guest. A possible molecular stacking of WOPESSCs—predicted on the basis of the polarized emission direction and the molecular TDMs of the guests (Supplementary Fig. 10)25—is illustrated in Fig. 3d and Supplementary Fig. 11. When only Pen is doped, we find that energy and polarization transfer can also occur (Supplementary Fig. 12). The CIE coordinates of a WOPESSC is (0.3258, 0.3396), nearly coinciding with the coordinate of standard white light (Fig. 3e). Interestingly, tunable white-light emission of WOPESSCs is observed. The extent of spectrum variation with polarization angle is inconsistent due to the different DOP values of the three main emission peaks. The CIE coordinates of WOPESSCs are (0.2753, 0.2993), (0.2788, 0.3026), (0.2977, 0.3192) and (0.3580, 0.3762) at polarized emission angles of 0°, 30°, 60° and 90°, respectively (Fig. 3e). The emission colour of WOPESSCs can be regulated from blue–white to yellow–white (Supplementary Table 1), showcasing its potential for diverse applications.
Fig. 3: Polarized fluorescence properties and schematic molecular packing of WOPESSCs.
a, Contour plots of polarized fluorescence spectra of a WOPESSC. b, Polar plot of intensity versus polarization angle for emission peaks in a WOPESSC. The periodically changing data points are fitted by α(δ)=αycos2(δ+?)+αxsin2(δ+?). See Supplementary Note 2 for details. c, Degree of polarization of emission peaks belonging to DPA (450 nm), Tc (500 nm) and Pen (610 nm) in four WOPESSCs. d, Schematic of the presumed molecular stacking of guest molecules in WOPESSCs. e, Fluorescence CIE diagrams of a WOPESSC (enclosed in a dashed circle) and WOPESSCs at different polarization angles.
Three-primary-colour optical imaging
We further investigate the suitability of WOPESSCs as a light source for optical imaging. Custom colour filters (Supplementary Figs. 13 and 14) and metal masks (Supplementary Fig. 15) are positioned between photoluminescent WOPESSCs (Fig. 2e) and a charge-coupled device, creating an optical imaging system (Fig. 4a). The emitted light from the WOPESSCs is shaped into red, green and blue emissive patterns, including ‘ICCAS UCAS’ (Fig. 4b), the Tianjin University logo (Fig. 4c) and the capital letters RGB (Fig. 4d). The spectra of the red, green and blue emissive images exhibit main emission peaks at 467 nm, 534 nm and 615 nm, respectively (Fig. 4e). The CIE coordinates corresponding to the red, green and blue emissions are (0.6551, 0.3126), (0.0361, 0.5788) and (0.1135, 0.1006), respectively. The colour gamut area formed by these CIE points covers 112% of the National Television System Committee standard (NTSC) standard (Fig. 4f), which greatly exceeds the commercial display panels. These findings highlight the immense potential of WOPESSCs as a background light source in display technology. As illustrated in Fig. 4g and Supplementary Fig. 16, the backlight source of photoluminescent WOPESSCs enables the uniform display of the three primary colour light-emitting units, showcasing the promising application prospects of WOPESSCs as a backlight source and chip-integrated micro/nanoscale light source.
Fig. 4: Optical imaging of WOPESSCs.
a, Schematic of the imaging system with photoluminescent WOPESSCs as the light source. b–d, Images of ICCAS and UCAS (b), the Tianjin University logo (c) and RGB (d) with photoluminescent WOPESSCs as the light source. Scale bar, 200 μm (b,c); 1.5 mm (d). e,f, Spectra (e) and corresponding CIE coordinates (f) of the three primary colours presented in d. g, The images of colour filters with photoluminescent WOPESSCs as the light source. Scale bar, 200 μm.
Organic polarized light-emitting diodes
White light is extensively used as a background light source in lighting and display technologies34,35,36. Our prepared WOPESSCs typically range in size from 30–70 μm; however, fabricating OLEDs that are based on 30–70 μm-sized WOPESSCs using traditional mask-based techniques is challenging. Here we develop a mask-free technique for constructing WOPESSCs–OPLEDs. This mask-free technique effectively leverages the thickness difference between the WOPESSC and the anode electrode, combined with the template peeling method. The device fabrication process is illustrated in Supplementary Fig. 17, with detailed descriptions provided in the ‘Device fabrication of OPLEDs and OPLETs’ section. The constructed WOPESSCs–OPLEDs have a multilayer structure, as shown in Fig. 5a. Supplementary Fig. 18 illustrates the schematic diagram of relative energy levels of the WOPESSCs–OPLEDs. The highest-occupied and lowest-unoccupied molecular orbitals of WOPESSCs were determined to be –5.6 and –2.6 eV, respectively. We therefore use transition MoO3 and LiF to modify the work functions of the silver and aluminium electrodes, respectively. We observe intense and uniform white-light emission (Fig. 5b, Supplementary Video 1 and Supplementary Fig. 19) with CIE coordinates of (0.3173, 0.3359). We find that a crystal thickness exceeding 250 nm will reduce the risk of breakdown and leakage. The emitting area of WOPESSCs–OPLEDs is determined by the size of crystals. The emitting size of WOPESSCs–OPLEDs can be reduced to around 10 μm, suggesting their great potential for WOPESSCs–OPLEDs in the future as high-resolution light sources.
Fig. 5: Polarized electroluminescence properties of WOPESSCs–OPLEDs.
a, Schematic diagram of the device structure of WOPESSCs–OPLEDs. NPB, N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine. b, Electroluminescence image of a WOPESSCs–OPLED operated at a high current density. Scale bar, 40 μm. c, Two-dimensional contour plots of polarized electroluminescence spectra of a WOPESSC–OPLED. d, Polar plot of the emission intensity at emission peak versus polarization angle. The periodically changing data points are fitted by α(δ)=αycos2(δ+?)+αxsin2(δ+?). See Supplementary Note 2 for details. e, A radar chart comparing optoelectronic performance of WOPESSCs with that of literature-reported white organic polarized emissive semiconductors. The whiteness index is defined as the extent to which the CIE coordinates of the sample approach (0.333, 0.333). It is calculated using |x – 0.333| + |y – 0.333|, where x and y are the CIE coordinates of the sample. A smaller index indicates a higher degree of whiteness in the emission.
For each polarization angle, the maximum electroluminescent spectrum of WOPESSCs–OPLEDs is extracted for analysing the polarized emission characteristics. The electroluminescence intensity gradually increases as the polarization angle varies from 90° to 180° (Supplementary Fig. 20). Figure 5c illustrates a 2D contour plot of the angle-resolved electroluminescent spectrum, demonstrating distinct polarization-dependent electroluminescence. The maximum (minimum) electroluminescence intensity occurs at 180° (90°), consistent with the observation of polarized fluorescence (where 0° and 180° of the polarizer align with the c-axis of WOPESSCs). The maximum DOP values of the electroluminescence emission are approximately 0.91, 0.66 and 0.65 for 450 nm, 500 nm and 610 nm, respectively (Fig. 5d). The variation of device current and photocurrent over time, as shown in Supplementary Fig. 21, effectively prevents overestimation of DOP due to device degradation. The calculated external quantum efficiency (EQE) and current efficiency values are 0.43% and 0.83 cd A–1, respectively (Supplementary Figs. 22 and 23). The maximum luminance and current density of WOPESSCs–OPLEDs are 1,997 mA cm–2 and 735 cd m–2, respectively (Supplementary Fig. 24). The EQE of WOPESSCs–OPLEDs are among the highest values reported for OLEDs based on white organic emissive semiconductors (Fig. 5e and Supplementary Table 2)18,19,30,37,38,39,40,41,42,43,44,45. It is believed that further enhancement in efficiency could be achieved by further increasing exciton utilization, balancing charge injection and transport as well as enhanced light coupling efficiency46. It is worth noting that as the current density increases, the white-light emission characteristics of the device remain stable, with little variation in CIE coordinates (Supplementary Fig. 25).
Organic polarized light-emitting transistors
Organic light-emitting transistors (OLETs)—a class of miniaturized optoelectronic devices that integrate the functionality of OLEDs12,47,48 and organic field-effect transistors (OFET)49,50,51,52 into a single device—are attracting increasing interest for potential applications in next-generation display technologies and micro/nanoscale light sources53,54,55,56,57,58,59,60. Construction of high-performance OLETs needs materials with high mobility and strong emission. Apart from the superior emission properties reported above, our WOPESSCs demonstrate high charge carrier mobility (Supplementary Figs. 26–28) due to the intrinsic charge transport property of DPA host molecules27. The highest mobility of WOPESSCs–OFETs is 4.9 cm2 V−1 s−1, with an average mobility of 3 cm2 V−1 s−1 from 24 WOPESSCs–OFETs (Supplementary Fig. 27d). This mobility represents the highest reported data among white organic emissive semiconductors (Fig. 5e and Supplementary Table 2).
The integrated high mobility and strong fluorescence properties of WOPESSCs enable their potential applications in OLETs. Single-crystal OPLETs with asymmetric electrodes are fabricated on the basis of WOPESSCs. The device structure and energy-level diagram are illustrated in Fig. 6a,b, with the device fabrication process detailed in ref. 29 as well as in Supplementary Fig. 29. The transistor performance of WOPESSCs–OPLETs—as measured by the transfer curves (Fig. 6c) and the corresponding output and photocurrent curves (Supplementary Fig. 30)—exhibits typical bipolar charge transport with hole (electron) mobilities of 0.23 (0.0015) cm2 V–1 s–1 and a maximum EQE of 1.1% (Supplementary Fig. 31). The DOP values of the WOPESSCs–OPLETs are approximately 0.9, 0.7 and 0.64 for 450 nm, 500 nm and 610 nm, respectively (Fig. 6d). Interestingly, there is a distinct transition in the spectrum (Fig. 6e), CIE coordinates (Fig. 6f and Supplementary Table 3) and electroluminescence colour (Supplementary Fig. 32) with increasing current density. Specifically, the CIE coordinates shift from (0.5691, 0.3554) to (0.2968, 0.2233), with minimum and maximum current densities of 2.5 × 10–2 and 86 kA cm–2, respectively (Supplementary Note 3). Note that, in comparison, no electrochromic effect was observed in the OLEDs (Supplementary Fig. 25), primarily due to the low current density of the device (with a maximum current density of 208 mA cm–2). It is noteworthy that this colour-changing process under gate voltage control can reverse during both forward and reverse scans, whereas WOPESSCs–OPLET maintains high polarization characteristics at different current densities (Supplementary Fig. 33). This change occurs because under strong electric field conditions, at lower current densities, there is a higher proportion of electron–hole recombination in Pen, which has the smallest band gap. As the current density increases, the number of electrons and holes increases, leading to a larger proportion of electron–hole recombination in the wide-band-gap host. These results validate the accuracy and feasibility of the proposed roadmap and enable the application of WOPESSCs in various micro/nanoscale polarized light-emitting devices.
Fig. 6: The optoelectronic properties of WOPESSCs–OPLETs.
a, Schematic diagram of WOPESSCs–OPLETs. PMMA, polymethyl methacrylate. b, Energy-level diagram of WOPESSCs–OPLETs. c, Transfer characteristics of a WOPESSC–OPLET at different negative and positive source–drain voltages. Ids, the channel current; A, ampere (the unit of current); Vg, gate voltage. d, Polar plot of emission intensity at middle current density versus polarization angle. The periodically changing data points are fitted by α(δ)=αycos2(δ+?)+αxsin2(δ+?). See Supplementary Note 2 for further details. e, Electroluminescence spectrum of a WOPESSC–OPLET at different current densities (with octadecyltrichlorosilane (OTS) as the interface modification layer). The minimum and maximum current densities for obtaining these spectra are 1.2 × 10–2 and 112 kA cm–2, respectively. f, Strong electroluminescent colour-tuning characteristics of the OPLET device, corresponding to changes in CIE coordinates.
Conclusion
The key to developing WOPESSCs is the rational selection of an intrinsically high-polarized superior optoelectronic blue-emitting DPA as the host molecule. The high similarity in molecular sizes, structures and matching energy levels between host and guests enables the growth of high-quality single crystals with efficient energy and polarization transfer. The obtained WOPESSCs exhibit excellent photoelectric performances with a high DOP ranging from 0.69 to 0.96, a high PLQY of 38.3%, a high mobility of 4.9 cm2 V–1 s–1, and CIE coordinates of (0.3258, 0.3396). The WOPESSCs demonstrate excellent three-primary-colour emissive characteristics in optical imaging with a colour gamut reaching up to 112% of NTSC, as well as tunable emission ranging from blue–white to yellow–white light. Furthermore, microscale WOPESSCs-based light-emitting diodes and transistors are successfully constructed, exhibiting high-polarized white electroluminescence and a unique capability for wide-range colour tunability under applied gate voltage. Our results undoubtedly prove the feasibility of the organic semiconductor single crystal route for creating highly polarized white emissive medium. The superiority of WOPESSCs positions them for a bright future in creating miniaturized high-performance OLEDs, OLETs and other related integrated circuits for various applications in lighting, displays, imaging and optical communications with white and full-colour emissions61,62,63.
Methods
Materials and instruments
To conduct our experiments, we used DPA as the host material and Tc and Pen as the guest materials. The host and guest materials were purchased from Hangzhou Order Science & Technology Company (Order Tech Inc.) and Sigma-Aldrich, respectively. The electrode target for thermal evaporation was purchased from ZhongNuo Advanced Material (Beijing) Technology Company. For characterization purposes, we employed XRD using an Empyrean instrument. Optical images and confocal fluorescence images were collected using OLYMPUS BX51 and OLYMPUS FV1000-IX81, respectively. Fluorescent photographs and spectra were characterized using an optical microscope system equipped with a spectrometer (EQPro, Ocean Opticals) and a digital charge-coupled device.
Preparation of single crystals
First, DPA was mixed with the guest molecules. Powder samples (Tc 3% and Pen 0.5%) were prepared by mixing DPA with these guests at the respective mass fractions. The resulting powders were ground thoroughly in a mortar with a small amount of acetone added. After grinding, the samples were placed in an oven and dried at 80 °C for 12 h. These samples were then used as feedstock for the growth of WOPESSCs. We attempted four different mass ratios of Tc 3% and Pen 0.5% (6:1, 4:1, 3:1 and 2:1) to optimize the preparation process for white emission. The quartz boat and quartz tube carrying the weighed powders were baked at 600 °C in the tube furnace (BTF-1200C, AnHui BEQ Equipment Technology Company) for 2 h before use to ensure a clean growth environment. The quartz tube carrying the quartz boat (which holds the powders) was placed into a tube furnace with a single temperature zone, where they were heated to 150 °C under vacuum (2.6 × 10–1 Pa) for 4–5 h. This results in the growth of WOPESSCs on a Si/SiO2/OTS substrate. The growth conditions for Pen 0.5% single crystals are the same as those for WOPESSCs.
Due to the poor solubility of DPA, Tc and Pen, preparing standard solutions with varying concentrations is challenging, making it difficult to determine the doping concentration of the guest molecules using the standard curve method based on the Beer–Lambert law. The mass fraction of the guest molecule in the mixed material was therefore used to represent the doping concentration.
Device fabrication of OFETs
We followed several steps to fabricate the WOPESSCs–OFETs. First, we cleaned conductively doped silicon wafers with a 300 nm silica layer using a wash solution (H2SO4:H2O2 = 7:3, volume ratio), followed by rinsing with pure water and oxygen plasma treatment. The OTS was then modified onto the Si/SiO2 substrate through a liquid-phase method (the silicon wafer is immersed in a solution of OTS in n-hexane, with a volume ratio of 1:1000 for OTS to n-hexane; after soaking for 6–8 h, it is sequentially washed with n-hexane, chloroform and isopropanol, followed by drying with nitrogen gas). We next grew WOPESSCs on the Si/SiO2/OTS substrate using the physical vapour transport method. Finally, gold electrodes were transferred to the surface of WOPESSCs using probes under a microscope.
Device fabrication of OPLEDs and OPLETs
WOPESSCs–OPLEDs were constructed using maskless technology (see Supplementary Fig. 17) as follows. First, WOPESSCs were grown on the substrate (Si/SiO2/OTS). TmPyPB (30 nm, 1 Å s–1), LiF (1.5 nm, 0.1 Å s–1) and aluminium (150 nm, 2–4 Å s–1) were then thermally evaporated onto the WOPESSCs/substrate (step 1). A drop of photopolymer (NOA63, Norland) was placed in the centre of the WOPESSCs/substrate. A clean glass was then placed flat on the WOPESSCs/substrate and pressed to spread the photopolymer evenly over the WOPESSCs/substrate (step 2). The photopolymer was cured using a ultraviolet lamp (250 W) for 1 min. The WOPESSCs/TmPyPB/LiF/Al was transferred onto the glass substrate by peeling (step 3). Finally, NPB (35 nm, 1 Å s–1), MoO3 (5 nm, 0.1 Å s–1) and silver (25 nm, 0.5 Å s–1) were sequentially evaporated onto the WOPESSCs/TmPyPB/LiF/Al/ photopolymer/glass (step 4).
The preparation process of the substrate Si/SiO2/OTS for OPLETs devices can be found in the ‘Device fabrication of OFETs’ section. The preparation process of the substrate Si/SiO2/PMMA for OPLETs devices can be found in ref. 29. The device fabrication process of OPLETs is detailed in previous report29 and Supplementary Fig. 29.
Testing of OFETs, OPLEDs and OPLETs
The WOPESSCs–OFETs were characterized in an atmospheric environment using the Keithley 4200-SCS. The mobility was calculated from the saturation region using the equation Ids = Ciμ(W/2 L)(VG – VT)2, where W and L are determined by the single crystals used in the device. Ci, capacitance of the dielectric layer; μ, the symbol representing mobility; VG, gata voltage; VT, threshold voltage. The electrical and optical tests of OPLEDs and OPLETs were performed by using the FS-PRO test system equipped with a spectrometer (EQPro, Ocean Optical) and a photomultiplier tube (Hamamatsu, H10721) in the glove box. The current density calculation for the OPLET device and the device’s EQE calculation are detailed in Supplementary Notes 3 and 4, respectively.
