Virtual screening is becoming a ground-breaking tool for molecular discovery due to the exponential growth of available computer time and constant improvement of simulation and machine learning techniques. We report an integrated organic functional material design process that incorporates theoretical insight, quantum chemistry, cheminformatics, machine learning, industrial expertise, organic synthesis, molecular characterization, device fabrication and optoelectronic testing. After exploring a search space of 1.6 million molecules and screening over 400,000 of them using time-dependent density functional theory, we identified thousands of promising novel organic light-emitting diode molecules across the visible spectrum. Our team collaboratively selected the best candidates from this set. The experimentally determined external quantum efficiencies for these synthesized candidates were as large as 22%.

Singlet fission can split a high energy singlet exciton and generate two lower energy triplet excito ns. This process has shown near 200 percent triplet exciton yield. Sensitizing solar cells with singlet fission material, it can potentially increase the power conversion efficiency limit from 29 percent to 35 percent. Singlet fission in the tetracene is known to be efficient, and the energy of the triplet excitons are energetically matched to the silicon bandgap. In this work, we designed an optical measurement with an external magnetic field to determine the efficiencies of triplet exciton transfer from tetracene to silicon. Using this method, we have found that a passivation layer of 8 angstroms of hafnium oxynitride on silicon allows efficient triplet exciton transfer around 133 percent.

Lead halide-based perovskite thin films have attracted great attention due to the explosive increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplettriplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross sections throughout the visible spectrum, as well as the strong spin-orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the additional tunneling barrier owing from the passivating ligands required for colloidal sensitizers. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination.

Multiexcited‐state phenomena are believed to be the root cause of two exigent challenges in organic light‐emitting diodes; namely, efficiency roll‐off and degradation. The development of novel strategies to reduce exciton densities under heavy load is therefore highly desirable. Here, it is shown that triplet exciton lifetimes of thermally activated delayed‐fluorescence‐emitter molecules can be manipulated in the solid state by exploiting intermolecular interactions. The external heavy‐atom effect of brominated host molecules leads to increased spin–orbit coupling, which in turn enhances intersystem crossing rates in the guest molecule. Wave function overlap between the host and the guest is confirmed by combined molecular dynamics and density functional theory calculations. Shorter triplet exciton lifetimes are observed, while high photoluminescence quantum yields and essentially unaltered emission spectra are maintained. A change in the intersystem crossing rate ratio due to increased dielectric constants leads to almost 50% lower triplet exciton densities in the emissive layer in the steady state and results in an improved onset of the photoluminescence quantum yield roll‐off at high excitation densities. Efficient organic light‐emitting diodes with better roll‐off behavior based on these novel hosts are fabricated, demonstrating the suitability of this concept for real‐world applications.

Figure 1. Homoconjugation and dihedral angle tuning. Scheme 1. Syntheses of Compounds 2−6 Communication pubs.acs.org/cm

Singlet exciton fission is a mechanism that could potentially enable solar cells to surpass the Shockley-Queisser efficiency limit by converting single high-energy photons into two lower-energy triplet excitons with minimal thermalization loss. The ability to make use of singlet exciton fission to enhance solar cell efficiencies has been limited, however, by the sparsity of singlet fission materials with triplet energies above the bandgaps of common semiconductors such as Si and GaAs. Here, we employ a high-throughput virtual screening procedure to discover new organic singlet exciton fission candidate materials with high-energy (>1.4 eV) triplet excitons. After exploring a search space of 4482 molecules and screening them using time-dependent density functional theory, we identify 88 novel singlet exciton fission candidate materials based on anthracene derivatives. Subsequent purification and characterization of several of these candidates yield two new singlet exciton fission materials: 9,10-dicyanoanthracene (DCA) and 9,10-dichlorooctafluoroanthracene (DCOFA), with triplet energies of 1.54 eV and 1.51 eV, respectively. These materials are readily available and low-cost, making them interesting candidates for exothermic singlet exciton fission sensitization of solar cells. However, formation of triplet excitons in DCA and DCOFA is found to occur via hot singlet exciton fission with excitation energies above ∼3.64 eV, and prominent excimer formation in the solid state will need to be overcome in order to make DCA and DCOFA viable candidates for use in a practical device.

which enable internal quantum efficiencies (IQEs) of up to 100%. [2,3] However, they rely on the use of expensive noble metals. [4] Moreover, blue phosphorescent emitters degrade rapidly, which result in low operational lifetimes. [5] As a consequence, blue colors are currently being produced by fluorescent emitters. Those emitters have long been limited to internal quantum efficiencies of 25% but can reach internal quantum efficiencies of up to 62.5% by employing triplet fusion. [6,7] Thermally activated delayed fluorescence (TADF) is a more efficient alternative to classical fluorescence and it can exhibit IQEs up to 100%. [8][9][10][11] In devices, three quarters of excitons are statistically formed in a triplet state, which are nonemissive in case of fluorescent emitters. [12] TADF molecules harness both singlet and triplet excitons by introducing appreciable reverse intersystem crossing (RISC) to convert nonemissive triplet excitons to emissive singlet excitons. [13,14] By spatially separating the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), the exchange energy is lowered and singlettriplet splitting (ΔE ST = E S1 − E T1 ) is reduced. [8] As a consequence, the singlet state becomes thermally accessible from the triplet state at room temperature. It has also been revealed that the resulting RISC proceeds via vibronic coupling of the triplet charge transfer state ( 3 CT) state with a triplet localized exciton state ( 3 LE), which in turn couples to the singlet manifold. [15] While many TADF molecules have been reported, [16][17][18][19][20][21][22] widely applicable molecular design principles beyond trial-anderror approaches remain scarce. [23][24][25] Recently, Adachi and coworkers [26] and Huang et al. [27] have shown that it is possible to enhance RISC in blue fluorescent molecules with carbazole donors by dihedral angle tuning (Figure 1a,b). The dihedral angle between donor and linker (θ 1 ) and the dihedral angle between linker and acceptor (θ 2 ) can be tuned by attaching methyl groups to the phenylene linker. Advantageously, this can be done without significantly changing emission wavelengths. As a result, deep blue emitters with external quantum efficiencies (EQEs) slightly above 10% were obtained. Herein, we report our latest efforts to test the general validity of the dihedral angle tuning strategy by applying it to a promising Efficient and stable blue emitters for organic light-emitting diodes are urgently needed for next-generation display and lighting applications. The discovery of thermally activated delayed fluorescence (TADF) has revealed a new class of promising candidates. After pairing the iminodibenzyl donor with the triazine acceptor via a phenylene linker, dihedral angle tuning is employed to regulate the difference between the energy levels of singlet and triplet excited states. Enhanced reverse intersystem crossing rates are observed in response to increased methylation at the phenylene linker. This behavior agrees with the density function...

Many efforts have been made to understand OLED degradation behavior. [3][4][5][6][7][8][9][10] While extrinsic degradation mechanisms have been identified and minimized, [11] routine identification of primary intrinsic degradation mechanisms has not been developed. Indeed, diagnostic spectr oscopy at the microscopic level is challenging given the exceedingly rare processes involved. Red phosphorescent OLEDs, for example, exhibit a decay time to 95% of initial luminance (LT95) of ≈20 000 h at an operating brightness of 1000 nits. [12] Given that the active phosphorescent dye is present at 3% loading in a 30 nm thick emissive layer, this yields more than 60 billion excitons per dye to LT90. One approach to the experimental challenge is to build models that consider an array of possible phenomena that are then fit to degradation data for a specific combination of materials in a specific device structure. [3,4,[13][14][15][16][17][18] Due to the multitude of fitting parameters, however, such models do not allow for an unequivocal, and more importantly, generalized quantification of physical parameters governing degradation.Given the challenges that confront the rational design of OLED materials, it is important to determine general characteristics of OLED failure processes by isolating individual key parameters in direct experimental probes. We focus on long-lived triplet excitons, which are common to all OLEDs, and are hypothesized as an important energy source for degradation processes. The total energy stored in triplet excitons is dependent on the triplet exciton density which, in turn, is determined by the triplet exciton generation rate, G, and the triplet exciton lifetime, τ. Using these two key parameters, we construct a simple model of OLED degradation based on three primary classes of known failure mechanisms.As shown in Table 1, the first class (i) of degradation mechanisms is unimolecular pathways. Examples include spontaneous degradation of a given molecule in its excited state, or an impurity-assisted process such as photo-oxidation. [19] Unimolecular processes are distinguished from the other classes because they scale linearly with the number of triplet excited states in the OLED. The second class (ii) of degradation mechanism is triplet-charge interactions. [14,20] Here, triplet excitons collide with a charged molecule, forming a high energy state which initiates permanent damage to one of the molecules. Assuming that the charge density is determined by nongeminate recombination, Organic light-emitting devices (OLEDs) are widely used for mobile displays, but the relatively short lifetime of blue OLEDs remains a challenge in many applications. Typically, instability is viewed as a material-specific chemical degradation problem. It is known to be alleviated by reducing the operating current or otherwise decreasing the exciton density. It is shown here that this view is incomplete. For archetypical phosphorescent materials, it is observed that the dependence of photostability on the triplet exciton life...