We show the effects of chlorine incorporation in the crystallization process of perovskite film based on a lead acetate precursor. We demonstrate a fabrication process for fast grain growth with highly preferred {110} orientation upon only 5 min of annealing at 100 °C. By studying the correlation between precursor composition and morphology, the growth dynamic of perovskite film in the current system is discussed. In particular, we found that both lead acetate precursor and Cl incorporation are beneficial to perovskite growth. While lead acetate allows fast crystallization process, Cl improves perovskite crystallinity. Planar perovskite solar cells with optimized parameters deliver a best power conversion efficiency of 15.0% and average efficiency of 14.0% with remarkable reproducibility and good stability.

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The addition of small seeding particles into a supersaturated solution is one among the most effective approaches to obtain high‐quality semiconductor materials via increased crystallization rates. However, limited study is conducted on this approach for the fabrication of perovskite solar cells. Here, a new strategy—“heterogenous seeding‐induced crystallization (hetero‐SiC)” to assist the growth of FAPbI3‐based perovskite is proposed. In this work, di‐tert‐butyl(methyl)phosphonium tetrafluoroborate is directly introduced into the precursor, which forms a low‐solubility complex with PbI2. The low‐solubility complex can serve as the seed to induce crystallization of the perovskite during the solvent‐evaporation process. Various in situ measurement tools are used to visualize the hetero‐SiC process, which is shown to be an effective way of manipulating the nucleation and crystal growth of perovskites. The hetero‐SiC process greatly improves the film quality, reduces film defects, and suppresses nonradiative recombination. A hetero‐SIC proof‐of‐concept device exhibits outstanding performance with 24.0% power conversion efficiency (PCE), well over the control device with 22.2% PCE. Additionally, hetero‐SiC perovskite solar cell (PSC) stability under light illumination is enhanced and the PSC retains 84% of its initial performance after 1400 h of light illumination.

Epitaxial growth gives the highest‐quality crystalline semiconductor thin films for optoelectronic devices. Here, a universal solution‐processed bottom‐up quasi‐epitaxial growth of highly oriented α‐formamidinium lead triiodide (α‐FAPbI3) perovskite film via a two‐step method is reported, in which the crystal orientation of α‐FAPbI3 film is precisely controlled through the synergetic effect of methylammonium chloride and the large‐organic cation butylammonium bromide. In situ GIWAXS visualizes the BA‐related intermediate phase formation at the bottom of film, which serves as a guiding template for the bottom‐up quasi‐epitaxial growth in the subsequent annealing process. The template‐guided epitaxially grown BAFAMA perovskite film exhibits increased crystallinity, preferred crystallographic orientation, and reduced defects. Moreover, the BAFAMA perovskite solar cells demonstrate decent stability, maintaining 95% of their initial power conversion efficiency after 2600 h ambient storage, and 4‐time operation condition lifetime enhancement.

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High performance organic photovoltaic devices typically rely on type-II P/N junctions for assisting exciton dissociation. Heremans and co-workers recently reported a high efficiency device with a third organic layer which is spatially separated from the active P/N junction; but still contributes to the carrier generation by passing its energy to the P/N junction via a long-range exciton energy transfer mechanism. In this study the authors show that there is an additional mechanism contributing to the high efficiency. Some bipolar materials (e.g., subnaphthalocyanine chloride (SubNc) and subphthalocyanine chloride (SubPc)) are observed to generate free carriers much more effectively than typical organic semiconductors upon photoexcitation. Single-layer devices with SubNc or SubPc sandwiched between two electrodes can give power conversion efficiencies 30 times higher than those of reported single-layer devices. In addition, internal quantum efficiencies (IQEs) of bilayer devices with opposite stacking sequences (i.e., SubNc/SubPc vs SubPc/SubNc) are found to be the sum of IQEs of single layer devices. These results confirm that SubNc and SubPc can directly generate free carriers upon photoexcitation without assistance from a P/N junction. These allow them to be stacked onto each other with reversible sequence or simply stacking onto another P/N junction and contribute to the photocarrier generation.

Excess PbI2 in perovskite film is an effective strategy for boosting perovskite solar cells (PSCs) performance. However, the presence of unreacted PbI2 is a critical source of intrinsic instability in perovskite under illumination, due to the photolysis of PbI2 (decomposed into metallic lead and iodine). Herein, this issue is solved by applying ionic liquids (ILs) on PSCs where the ILs can form types of stable supramolecules with residual lead iodide. The formation process and mechanism of the supramolecules are elucidated. The residual PbI2 is also revealed to cause high level lead interstitial defects and induced tensile strain which further deteriorate device performance. The self‐assembled supramolecular complex can passivate the PSCs where significant enhancements are achieved in both power conversion efficiency (PCE, from 21.9% to 23.4%) and device stability (retaining 95% of the initial PCE after 4080 h in ambient dry‐air storage, and 80% after 1400 h continuous light illumination).

Causes of efficiency limitation in common fluorescence and phosphorescence hybrid white organic light-emitting devices (WOLEDs) are discussed, and a new device architecture is proposed to address these issues. This architecture employs a fluorescent emitting layer (EML) of blue exciplex-forming cohost, which shows broad and strong thermally activated delayed fluorescence (TADF). Hybrid WOLEDs based on this architecture not only allow complete triplet harvesting for light generation but also can achieve white light emission with high color rending indexes (CRI) using only two colors. By using 26DCzPPy:PO-T2T as the blue fluorescent EML and 26DCzPPy:Ir complexes as the phosphorescent EML, we prepared a series of two-color WOLEDs with low turn-on voltages of 2.5-3.3 V, high forward-viewing EQEs of 12.7-19.3% and high CRIs of 67-77. These results suggest this new architecture would be an effective way to achieve high performance WOLEDs with simple structures.