Efficient deep-blue non-doped organic light-emitting diode with improved roll-off of efficiency based on hybrid local and charge-transfer excited state

High-efficiency deep-blue light-emitting materials are of significance in the fields of commercial full-color displays and solid-state lightings. A hybrid local and charge-transfer (HLCT) excited state not only favors deep-blue emission avoiding a large redshift from a strong charge-transfer (CT) state, but also simultaneously harvests both high photoluminescence efficiency and high exciton-utilizing efficiency. Herein, we report a new V-shaped acceptor-donor-acceptor (A-D-A) type molecule TPA-2PPI with an HLCT emissive state, which is modified from D-A type TPA-PPI. The non-doped device based on the TPA-2PPI emitter still exhibits deep-blue emission peaking at 452 nm with a full width at half maximum (FWHM) of only 50 nm and Commission International de L'Eclairage (CIE) coordinates of (0.151, 0.108). Compared with TPA-PPI, the electroluminescence (EL) not only maintains high efficiency with a maximum external quantum efficiency (EQE) of 4.91%, but also the EL device displays a significantly slower roll-off of efficiency at high luminances with an EQE of 4.89% (or 4.56%) at 100 cd m(-2) (or 1000 cd m(-2)), which is confidently beneficial for the operative stability of OLED devices.

高效深蓝色发光材料在商业全彩显示器和固态照明领域具有重要意义。混合局域和电荷转移（HLCT）激发态不仅有利于深蓝色发光，避免了强电荷转移（CT）态引起的大幅红移，而且同时实现了高光致发光效率和高激子利用效率。在此，我们报道了一种具有HLCT发射态的新型V形受体 - 给体 - 受体（A - D - A）型分子TPA - 2PPI，它是由D - A型TPA - PPI改性而来。基于TPA - 2PPI发光体的非掺杂器件仍然呈现出在452 nm处峰值的深蓝色发光，半峰宽（FWHM）仅为50 nm，国际照明委员会（CIE）坐标为（0.151，0.108）。与TPA - PPI相比，电致发光（EL）不仅保持了高效率，最大外量子效率（EQE）为4.91%，而且该EL器件在高亮度下效率衰减明显更慢，在100 cd/m²（或1000 cd/m²）时EQE为4.89%（或4.56%），这无疑有利于有机发光二极管（OLED）器件的工作稳定性。