No abstract

Record power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have been obtained with the organic hole transporter 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenyl-amine)9,9′-spirobifluorene (spiro-OMeTAD). Conventional doping of spiro-OMeTAD with hygroscopic lithium salts and volatile 4- tert -butylpyridine is a time-consuming process and also leads to poor device stability. We developed a new doping strategy for spiro-OMeTAD that avoids post-oxidation by using stable organic radicals as the dopant and ionic salts as the doping modulator (referred to as ion-modulated radical doping). We achieved PCEs of >25% and much-improved device stability under harsh conditions. The radicals provide hole polarons that instantly increase the conductivity and work function (WF), and ionic salts further modulate the WF by affecting the energetics of the hole polarons. This organic semiconductor doping strategy, which decouples conductivity and WF tunability, could inspire further optimization in other optoelectronic devices.

Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives.

Interfacial reactions between the perovskite emitters and the interlayers are detrimental to the operational stability of the perovskite light-emitting diodes. Incorporating dicarboxylic acids into the precursor efficiently eliminates reactive organic ingredients in the perovskite emitters through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate underneath. The formed amides improve the stability of the perovskite emitters and the charge injection contacts, ensuing notably improved operational stability of the resulting perovskite light-emitting diodes.

To clarify the problem of undesired crystallization of amorphous aluminosilicate inorganic polymers (AIPs) accompanied by the loss of mechanical properties, we synthesized two types of chemically identical AIPs that differ in durability under hydrothermal conditions. Whereas phase-stable AIPs remain amorphous, phase-unstable AIP systems undergo extensive crystallization with the formation of high fractions of chabasite and zeolite P. The application of 27 Al MQ/MAS and { 1 H}-REDOR-27 Al MQ/MAS NMR spectroscopies, combined with the recently developed biaxial shearing transformations, revealed a two-component character of the prepared AIPs. The prevailing fraction of [AlO 4 ] − species (amorphous phase) is charge-balanced by Na + counterions and exhibits considerable distribution of 27 Al chemical shifts induced by the variation of Al−O−Si valence angles. In contrast, the minor fraction of [AlO 4 ] − tetrahedra, which can be attributed to the partially ordered domains of aluminosilicate networks, shows a broad distribution of quadrupolar parameters that result from variability in the chemical nature of the counterions. A comparison of the prepared AIPs revealed that the partially ordered domains of the phase-unstable AIPs contained a considerably larger amount of [AlO 4 ] − species charge-balanced by H + . Therefore, we assume that the destabilization of AIPs is associated with the presence of bridging hydroxyl groups (Si−OH + −Al, Brønsted-acid sites) that induce breaking of Si−O−Al bonds. The resulting decrease in network density can induce a temporal release of extraframework Al species, their subsequent rearrangement, and the formation of a crystalline phase. The process of crystallization is supported by the higher mobility of proton species as revealed by a range 1 H-receptive MAS NMR experiments. In contrast, the factors that stabilize amorphous nature of aluminosilicate frameworks are the presence of four-coordinate extraframework Al species, such as Al(OH) 3 + or AlOH 2+ −H 2 O, and tight incorporation of proton fraction into the inorganic matrix.