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Lead sulphide (PbS) nanocrystals (NCs) are promising materials for low-cost, high-performance optoelectronic devices. So far, PbS NCs have to be first synthesized with long-alkyl chain organic surface ligands and then be ligand-exchanged with shorter ligands (two-steps) to enable charge transport. However, the initial synthesis of insulated PbS NCs show no necessity and the ligand-exchange process is tedious and extravagant. Herein, we have developed a direct one-step, scalable synthetic method for iodide capped PbS (PbS-I) NC inks. The estimated cost for PbS-I NC inks is decreased to less than 6 $·g−1, compared with 16 $·g−1 for conventional methods. Furthermore, based on these PbS-I NCs, photodetector devices show a high detectivity of 1.4 × 1011 Jones and solar cells show an air-stable power conversion efficiency (PCE) up to 10%. This scalable and low-cost direct preparation of high-quality PbS-I NC inks may pave a path for the future commercialization of NC based optoelectronics.

Current efforts on lead sulfide quantum dot (PbS QD) solar cells are mostly paid to the device architecture engineering and postsynthetic surface modification, while very rare work regarding the optimization of PbS synthesis is reported. Here, PbS QDs are successfully synthesized using PbO and PbAc · 3H O as the lead sources. QD solar cells based on PbAc-PbS have demonstrated a high power conversion efficiency (PCE) of 10.82% (and independently certificated values of 10.62%), which is significantly higher than the PCE of 9.39% for PbO-PbS QD based ones. For the first time, systematic investigations are carried out on the effect of lead precursor engineering on the device performance. It is revealed that acetate can act as an efficient capping ligands together with oleic acid, providing better surface coverage and replace some of the harmful hydroxyl (OH) ligands during the synthesis. Then the acetate on the surface can be exchanged by iodide and lead to desired passivation. This work demonstrates that the precursor engineering has great potential in performance improvement. It is also pointed out that the initial synthesis is an often neglected but critical stage and has abundant room for optimization to further improve the quality of the resultant QDs, leading to breakthrough efficiency.

via endothermally assisted reverse intersystem crossing (RISC), thereby achieving a theoretical 100% exciton utilization. [1b,3,4] The strategy for a sufficiently small ΔE ST is to reduce the electron exchange of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) by separating them into different segments. [5][6][7][8] As a classic example, a donor-π-acceptor (D-π-A) molecular architecture can form a twisted conformation at excitation and induce effective charge transfer (CT) along with the HOMO (@ donor) and LUMO (@ acceptor) separation. [6,9] The structure relaxation between the ground and twist induced excited states, however, inevitably results in large Stokes shift and broad CT emission, which is extremely detrimental to the color purity of the emitters for high-resolution display applications.In an exceptional solution for this problem proposed by Hatakeyama et al., a series of N/B rigid heterocycles were used as multiple resonances induced TADF (MR-TADF) emitters based on a DABNA-1 core to show good color purity. [10] Different from the D-π-A type TADF emitters, these MR-TADF emitters possess a rigid configuration and realize the HOMO and LUMO separation by opposite resonance effect of the nitrogen and boron atoms. Very recently, by modifying the original DABNA-1 with a peripheral carbazole group, Zheng and co-workers obtained a more efficient MR-TADF emitter TBN-TPA, and the corresponding device realized a maximum external quantum efficiency (EQE max ) of 32.1% and a sharp blue emission peak with full-width at half-maximum (FWHM) of 27 nm, showing the potential of MR-TADF. [11] However, the attempts with oxygen atoms replacing nitrogen atoms as the electron-donating group in a polycyclic framework did not activate the TADF phenomenon, [12] indicating new MR-TADF systems need more investigation and the versatility of the molecular design should be further explored.In this work, we design a novel system bearing MR-TADF activity aside from the reported N/B system, which consists of rigidified aryl ketones and amine. In the previous study, carbonyl group was widely used as a functional motif for room temperature phosphorescent materials and TADF emitters, owing to the electron-withdrawing nature and the small ΔE ST caused by its electronic transition from the n orbital to Multiple resonances induced thermally activated delayed fluorescence (MR-TADF) has great advantages in high color purity display. Up to now, current MR-TADF emitters are only based on the boron-nitrogen-containing fragment. Reported herein is a novel class of MR-TADF emitter, quinolino[3,2,1-de]acridine-5,9-dione (QAO), realized by the opposite resonance effect of the carbonyl and the nitrogen atoms, which is also the smallest TADF emitter reported so far. The QAO-based pure blue organic light-emitting diode achieves a maximum external quantum efficiency (EQE max ) of 19.4% with a small full width at half maximum of 39 nm. Moreover, tert-butyl modified QAO can be employed as an efficient electr...