Manipulating Crystal Growth and Secondary Phase PbI2 to Enable Efficient and Stable Perovskite Solar Cells with Natural Additives.

In perovskite solar cells (PSCs), the inherent defects of perovskite film and the random distribution of excess lead iodide (PbI2) prevent the improvement of efficiency and stability. Herein, natural cellulose is used as the raw material to design a series of cellulose derivatives for perovskite crystallization engineering. The cationic cellulose derivative C-Im-CN with cyano-imidazolium (Im-CN) cation and chloride anion prominently promotes the crystallization process, grain growth, and directional orientation of perovskite. Meanwhile, excess PbI2 is transferred to the surface of perovskite grains or formed plate-like crystallites in local domains. These effects result in suppressing defect formation, decreasing grain boundaries, enhancing carrier extraction, inhibiting non-radiative recombination, and dramatically prolonging carrier lifetimes. Thus, the PSCs exhibit a high power conversion efficiency of 24.71%. Moreover, C-Im-CN has multiple interaction sites and polymer skeleton, so the unencapsulated PSCs maintain above 91.3% of their initial efficiencies after 3000 h of continuous operation in a conventional air atmosphere and have good stability under high humidity conditions. The utilization of biopolymers with excellent structure-designability to manage the perovskite opens a state-of-the-art avenue for manufacturing and improving PSCs.

Aggregation-regulated room-temperature phosphorescence materials with multi-mode emission, adjustable excitation-dependence and visible-light excitation.

Constructing room-temperature phosphorescent materials with multiple emission and special excitation modes is fascinating and challenging for practical applications. Herein, we demonstrate a facile and general strategy to obtain ecofriendly ultralong phosphorescent materials with multi-mode emission, adjustable excitation-dependence, and visible-light excitation using a single organic component, cellulose trimellitate. Based on the regulation of the aggregation state of anionic cellulose trimellitates, such as CBtCOONa, three types of phosphorescent materials with different emission modes are fabricated, including blue, green and color-tunable phosphorescent materials with a strong excitation-dependence. The separated molecularly-dispersed CBtCOONa exhibits blue phosphorescence while the aggregated CBtCOONa emits green phosphorescence; and the CBtCOONa with a coexistence state of single molecular chains and aggregates exhibits color-tunable phosphorescence depending on the excitation wavelength. Moreover, aggregated cellulose trimellitates demonstrate unique visible-light excitation phosphorescence, which emits green or yellow phosphorescence after turning off the visible light. The aggregation-regulated phenomenon provides a simple principle for designing the proof-of-concept and on-demand phosphorescent materials by using a single organic component. Owing to their excellent processability and environmental friendliness, the aforementioned cellulose-based phosphorescent materials are demonstrated as advanced phosphorescence inks to prepare various disposable complex anticounterfeiting patterns and information codes.

Cellulose-Based Ultralong Room-Temperature Phosphorescence Nanomaterials with Tunable Color and High Quantum Yield via Nano-Surface Confining Effect.

How to achieve multicolor organic room-temperature phosphorescence (RTP) is still challenging and striking. Herein, we discovered a new principle to construct eco-friendly color-tunable RTP nanomaterials based on the nano-surface confining effect. Cellulose nanocrystal (CNC) immobilized cellulose derivatives (CX) containing aromatic substituents via hydrogen-bonding interactions, which effectively inhibit the motion of cellulose chains and luminescent groups to suppress the nonradiative transitions. Meanwhile, CNC with a strong hydrogen-bonding network can isolate oxygen. CX with different aromatic substituents regulate the phosphorescent emission. After mixing CNC and CX directly, a series of polychromatic ultralong RTP nanomaterials were obtained. The RTP emission of the resultant CX@CNC can be finely adjusted through the introduction of various CX and the regulation of the CX/CNC ratio. Such a universal, facile, and effective strategy can be used to fabricate various colorful RTP materials with wide color gamut. Because of the complete biodegradability of cellulose, the multicolor phosphorescent CX@CNC nanomaterials can be used as eco-friendly security inks to fabricate disposable anticounterfeiting labels and information-storage patterns via conventional printing and writing processes.

Ultralong phosphorescence cellulose with excellent anti-bacterial, water-resistant and ease-to-process performance.

Herein, we present a phosphorescent cationized cellulose derivative by simply introducing ionic structures, including cyanomethylimidazolium cations and chloride anions, into cellulose chains. The imidazolium cations with the cyano group and nitrogen element promote intersystem crossing. The cyano-containing cations, chloride anions and hydroxyl groups of cellulose form multiple hydrogen bonding interactions and electrostatic attraction interactions, effectively inhibiting the non-radiative transitions. The resultant cellulose-based RTP material is easily processed into phosphorescent films, fibers, coatings and patterns by using eco-friendly aqueous solution processing strategies. Furthermore, after we construct a cross-linking structure by adding a small amount of glutaraldehyde as the cross-linking agent, the as-fabricated phosphorescent patterns exhibit excellent antibacterial properties and water resistance. Therefore, considering the outstanding biodegradability and sustainability of cellulose materials, cellulose-based easy-to-process RTP materials can act as antibacterial, water-resistant, and eco-friendly phosphorescent patterns, coatings and bulk materials, which have enormous potential in advanced anti-counterfeiting, information encryption, disposable smart labels, etc.

Irreversible Humidity-Responsive Phosphorescence Materials from Cellulose for Advanced Anti-Counterfeiting and Environmental Monitoring.

Organic phosphorescence materials have many unique advantages, such as a large Stokes shift, high signal-to-noise ratio, and no interference from background fluorescence and scattered light. But, they generally lack responsiveness. Herein, we developed a new type of biopolymer-based phosphorescence materials with excellent processability and irreversible humidity-responsiveness, via introducing the imidazolium cation to cellulose chain. In the resultant cellulose derivatives, the imidazolium cation promotes the intersystem crossing, meanwhile the cation, chloride anion, and hydroxyl group form multiple hydrogen bonding interactions and electrostatic attraction interactions, which successfully inhibit the nonradiative transitions. As a result, the ionic cellulose derivatives exhibit green phosphorescence at room temperature and can be processed into phosphorescent films, coatings, and patterns. More interestingly, their phosphorescence emission changes when the different processing solvents are used. The ionic cellulose derivatives processed with acetone have a negligible phosphorescence, while they give an irreversible humidity-responsive phosphorescence, which means that the ionic cellulose derivatives processed with acetone exhibit significantly enhanced phosphorescence once they meet water vapor. Such novel irreversible responsive phosphorescence materials have huge potential in advanced anticounterfeiting, information encryption, molecular logic gates, smart tags, and process monitoring.