Pursuing electrically pumped lasing with organic semiconductors

Challenges and opportunities:•The pursuit of electrically pumped organic lasers remains a grand challenge due to unbalanced optical gain carrier mobility, as well triplet losses associated with electrical injection into the semiconductors.•Recent progresses respect molecular design, theoretical prediction, device fabrication for light-emitting semiconductors inspire us that deep understanding relationship between lasing emissions structures, engineering, exciton dynamics might stand out most promising way toward this pursuit.•The achievement will certainly help bridge gap current microelectronic circuits their nanophotonic counterparts, thus revolutionizing field displays, medical treatments, communication. Electrically have been eagerly sought several decades, although they not fully demonstrated yet. Recently, impressive made semiconductors. In perspective, we outline key issues balanced gain, excitonic other challenges pump after examining breakthroughs in recent efforts. Then, provide concise overview potential solutions from viewpoint principle by exploring dynamics, which driven IntroductionSince discovery optically laser action dye-doped systems1Soffer B.H. McFarland B.B. Continuously tunable, narrow-band dye lasers.Appl. Phys. Lett. 1967; 10: 266-267Google Scholar,2Peterson O.G. Snavely Stimulated emission flashlamp-excited dyes polymethyl methacrylate.Appl. 1968; 12: 238-240Google Scholar crystals,3Karl N. Laser an crystal.Phys. Stat. Sol. (A). 1972; 13: 651-655Google Scholar,4Avanesjan O.S. Benderskii V.A. Brikenstein V.K. Broude V.L. Korshunov L.I. Lavrushko A.G. Tartakovskii I.I. Anthracene crystals under intensive pumping.Mol. Cryst. Liq. 1974; 29: 165-174Google solid-state investigated intensively applications communication, display, sensing, owing high monochromaticity brightness emissions, outstanding solution processability, remarkable flexibility, broad spectral tunability materials.5Samuel I.D.W. Turnbull G.A. 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Funct. 2009; 19: 1360-1370Google proposed transistor (LET) integrated (DFB) resonator lasing, offers route achieving EPOL architecture type. Until 2019, Adachi al.23Sandanayaka A.S.D. Matsushima Bencheikh Terakawa Potscavage W.J. Qin C. Fujihara Goushi Ribierre J.-C. Indication current-injection semiconductor.Appl. Express. 2019; 12061010Google showed plausible experimental example molecule combined mixed-order DFB grating, provides strong indication research community probably coming soon.However, lack roles materials, devices, photophysics so far no case has yet unambiguously met all following criteria EPOLs24Samuel Namdas E.B. How recognize lasing.Nature 3: 546-549Google Scholar: sufficient densities induce population inversion, threshold behavior current-density-dependent narrowing output power enhancement, observation both spatial temporal coherence. Therefore, it necessary at moment summarize studies material excited-state process ultimate goal many years area optoelectronics.The mentioned earlier claiming pumping (e-pumping) can be elaborated follows. (1) Population inversion. There should For example, typical (Pth) reported around 1 ?J·cm?2 excitation wavelength (?) 400 nm. Considering materials thickness (z) 500 nm absorb 80% energy, could obtain excitons stimulated (i.e., inversion) Nth = 0.8Pth/[z(hc/?)], where h Planck constant c velocity vacuum. Accordingly, density, Nth, determined about 3.4 × 1016 cm?3. The e-pumping achieve same density inversion (Figure 1A) higher than aroused electric contacts, injected charges, annihilation. Assuming additional losses, lowest limit Jth, then estimated using equation, Jth ? q Wrz/(? ? ?), elementary charge, Wrz (?50 nm) width recombination zone, ? (?40%)23Sandanayaka ratio confined active region total field, (=0.25) singlet generation ratio, ? (?1 ns) lifetime excitons. obtained approximately 0.27 kA·cm?2. Nevertheless, usually exists would increase 1–10 addition, thresholds 10–100 ?J·cm?2, result even 100–1,000 It noteworthy mention only survive 0.1–1 kA·cm?2, few them conductive stable enough 10 represents 1–2 magnitude order lower desired Very recently, ultra-low ?0.1 (corresponding ?1 kA·cm?2 taking consideration) achieved excitation, resulted realization quasi-continuous-wave laser.25Sandanayaka Yoshida Inoue J.C. Toward continuous-wave operation lasers.Sci. Adv. 2017; e1602570Google From design point view, possible decrease threshold, enhance capability optimize energy levels played lasing. Moreover, able reduce reachable level aspect engineering employing high-Q resonators optimizing structures. (2) Threshold behavior. enhancement observed. At low grew steadily. When exceeded peak increased rapidly superlinearly accompanied sharp full-width half-maximum (FWHM), indicates occurrence 1B). (3) Temporal confirmed coherence beam. time derived linewidth relation ?coherence ?2/(c??), ? wavelength, ?? line width, speed light, while directly imaged real space interference patterns.It noted reviews constructed different aspects,5Samuel Scholar,26Bisri S.Z. Takenobu Iwasa electrically-driven lasers.J. Chem. 2014; 2827-2836Google 27Kuehne A.J.C. Gather developments geometries, techniques.Chem. 116: 12823-12864Google 28Zhang Dong Hu W. electronics photonics.Adv. 30: e1801048Google 29Jiang Liu Y.-Y. Lin Gao Lai W.-Y. view future development.Chem. Soc. 2020; 49: 5885-5944Google but paper clearly clarify photophysics, perspective basic structure-property highly demanded EPOLs. first breakthrough (lasing occurs if outcompetes loss resonator) optimizations, management. We anticipate insight fundamental principles boost next-generation source also attract more researchers communities chemistry, science, physics, etc., contribute field.Key EPOLsThe main stumbling blocks prevented upon direct attributed issues.30Baldo R.J. Prospects lasers.Phys. B. 2002; 66: 035321Google conflicting requirements mobility materials. Generally, excellent calls coupling neighboring coplanar molecules solid-state, close packing leads efficiency. synthesis luminescent yield step induced non-radiative According spin statistics, carriers (electrons holes) generate (S1) (T1) 1:3 triplets produce cases, smaller cross-section absorption. This severely limits internal efficiencies leading significantly continuous high-density (both singlets triplets) accumulate get overlapped each other, results absorption, carriers-exciton quenching, singlet-triplet annihilation (STA), triplet-triplet (TTA), absorption polarons, dissipating elevating threshold. Thus, overcoming caused particularly important excitation. Other related electrode loss, thermal conductivity, limited operational stability etc.Potential EPOLsMaterial designOrganic need compensate within systems. Together coefficient, conductivity decent support electrons holes retaining gain. One fluorene-based molecules,31Liu De Ou Li Z. Liao Xu al.Organic photoluminescence yield, deep-blue characteristics.J. Am. 142: 6332-6339Google Scholar,32Yap B.K. Xia Campoy-Quiles Stavrinou P.N. D.D. 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Y80F8:20F5 BP3T electron, threshold.(B) Triplet-related S1 T1 including TA (T1?Tn), TTA, STA, dissipate elevate Several managers resolve earlier, TQer loss. employment RISC suppress accumulation regenerated singlets, may S0.(C) Triplet managers, (9,10-di(naphtha-2-yl)anthracene, ADN) (4,4?-bis[(N-carbazole)styryl]biphenyl, BSBCz).View Large Image ViewerDownload Hi-res image Download (PPT)Regarding simultaneous essential understand properties intermolecular interactions. general, electronic couplings, transfer integrals reorganization enable transport. prefer stack face-to-face configuration, makes forbidden transition originated net zero dipole molecules. Meanwhile, noncoplanar steric side chains rotating features shown weakened interaction, favorable exhibits rather mobility. compromised approach balance tune aggregation mode via rational design. Based previous investigation, shifting aggregates configuration herringbone stacking face-to-edge alignment, reduced, gives rise improved performances maintaining properties. As such, arrangement allows modulation utilized EPOLs.28Zhang Indeed, elusive, explored yet, emissive recently.31Liu 32Yap 33Bisri 34Gundlach 35Fang 36Wang 37Wang Scholar,40Li Y.-X. Yu M.-N. X.-M. C.-J. Eginligil R.-Q. X.-W. Nie Y.-J. Xie L.-H. al.Wide-bandgap nanocrystals tunable 2021; 9: 3171-3176Google Scholar,41Li C.-X. 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