Research highlights
1. A series of stable perovskite nanocrystals ( PNCs ) based on dendritic ammonium ligands were prepared.
2. The increase of ligands from G1 to G2 was studied , and the high stability and ability of PNSc to resist anion exchange in hydrothermal environment and trimethylsilyl iodide (strong iodine source) were studied.
3. Design of a self-powered glass interlayer that simultaneously serves as the absorptive emitter of fluorescent solar concentrators ( LSCs ) and the emitter of white light glass.
1. Problems in the application of perovskite nanocrystals in building photovoltaic self-power supply
Lighting accounts for 17 % of total energy consumption in buildings and is a major consumer of electricity in the commercial sector. Ideally, window glass can better generate electricity during the day without affecting the transmission of sunlight, and use the energy generated during the day to emit white light for indoor lighting at night. To realize such self-powered buildings, fluorescent solar concentrators ( LSCs ) may be an ideal choice. Among various phosphors, metal halide perovskite nanocrystals ( PNCs ) can Unique properties such as tonality, high brightness (up to 100% photoluminescence quantum yields ( PLQYs ) ) and easy solution processing have proven to be an ideal choice. So far, research activities on perovskite-containing LSCs have been mainly limited to the synthesis of single-color PNCs , whose emission and absorption ranges are narrower than sunlight. Mixing colored PNCs is the preferred strategy to directly broaden the emission and absorption range, thereby maximizing the utilization of sunlight in LSCs , and simultaneously fabricating fully perovskite-based white light-emitting diodes ( WLEDs ) without the use of additional phosphors. However, due to the ionic properties of perovskites, the mixing of different phase PNCs can easily lead to structural collapse, directly limiting their applications. Therefore, there is an urgent need to develop optically suitable and robust perovskite nanocrystals and use them in the fabrication of advanced devices.
2. Introduction to results
In view of this, Qin Tianshi's research group at Nanjing University of Technology reported a class of dendritic ammonium ligands as hard-shell encapsulated metal halide perovskite nanocrystals ( PNCs ) to improve their stability and suppress hybrid colloidal perovskite nanocrystals. Ion penetration in crystal solutions. The as-synthesized ligand-encapsulated PNCs significantly achieve nearly uniform photoluminescence quantum yields ( PLQYs ) and strongly resist ion exchange reactions under strong anion source attack. Stable hybrid colored PNCs were embedded in laminated glass to prepare self-powered white light glass, which simultaneously serves as the absorbing emitter of fluorescent solar concentrators ( LSCs ) and the emitter of white light glass.
3. Results and Discussion
Point 1 : Encapsulation of organic dendritic ammonium-based ligands
The authors synthesized two organic dendritic ammonium-based ligands ( G1 and G2 ) and then used them directly for the in situ synthesis of CsPbX nanocrystals (Figure 1 ) . As the ligand complexity increases from G1 to G2 , the stability of PNCs (in terms of air, water, heat, and resistance to anion exchange) increases accordingly due to the rigid ligand shell formed by π conjugation and intermolecular interactions. . Furthermore, the PLQY values of dendritically stabilized CsPbBr 3 NCs were found to be close to consistent. The mixed stable green and red emission of G2-GPNCs and G2-RPNCs was directly applied to prepare blue-light pumped WLEDs , while the same aqueous suspension of G2-GPNCs and G2-RPNCs was also applied to prepare by ultrasonic spraying and hot pressing methods. Self-powered white light emitting glass in which PNCs act as phosphors, both for LSCs and for white light emission.
Figure 1 Perovskite nanocrystal packaging solution
Dendritic CsPbBr 3 PNCs ( G1-GPNCs and G2-GPNCs ) were synthesized by hot injection technology , and an appropriate amount of G1 or G2 was introduced into the reaction medium as a ligand before injecting cesium oleate. Instantly, a green solution appeared, indicating the formation of PNCs . For comparison, a control sample of PNCs (labeled Ola-GPNCs ) was also prepared using oleylamine as the only amine ligand . The PL peak positions of Ola-GPNCs , G1-GPNCs and G2-GPNCs are 517 nm , respectively , and the half-peak widths are 19.8 , 19.5 and 19.6 nm, respectively (Fig. 2a ). The PLQY of Ola-GPNCs was calculated to be 80% , while in the G1-GPNCs and G2-GPNCs samples, the PLQY reached close to unit levels ( 98.8% and 99.95% , respectively ) (Figure 2b ). In addition, time-resolved photoluminescence measurements determined the fluorescence lifetimes of Ola-GPNCs , G1-GPNCs and G2-GPNCs in toluene to be 40 , 48.3 and 64.7 ns, respectively (Fig. 2c ), indicating that G1 and G2 effectively modified the PNCs surface defects, thus inhibiting non-radiative pathways. As shown in Figure 2d , all X -ray diffraction ( XRD ) peaks of CsPbBr3P NCs match the orthorhombic crystal phase of CsPbBr3 .
Figure 2 Optical, structural, morphological and compositional analysis of synthesized G1-GPNC and G2-GPNC
Point 2 : Stability of dendritic ammonium-terminated PNCs
In order to study the stability of dendritic ammonium-based encapsulated PNCs , the authors studied samples under different conditions. In all samples, after 20 days of storage at room temperature, there was no obvious change in the XRD signal (Fig. 3a ). However, the TEM , shown in Fig. 3b , showed an obvious large-area amorphous structure, indicating that Ola -GPNCs undergo severe degradation. However, the G1-GPNCs to G2-GPNCs samples (Figures 3c and 3d ), especially G2-GPNCs , maintained the integrity of the cubic shape. The PL intensity evolution of G1-GPNCs and G2-GPNCs showed superior stability compared with traditional Ola -encapsulated CsPbBr 3 PNCs (Fig. 3e ). During the 20- day storage of G1-GPNCs and G2-GPNCs , the intensity remained at 77% and 84% of the initial PL intensity , with almost no movement of the peak position. In the photos of these samples, after 20 days of storage, the Ola-GPNCs solution became colorless and severely aggregated into an insoluble yellow precipitate.
Figure 3 Stability monitoring of dendritic ammonium-terminated PNCs
After 10 days of storage , the samples were evaluated for stability at 50 ° C ; PL spectra were collected after different time intervals (Fig. 3f ). Among the three samples, G2-GPNCs showed the highest thermal stability, retaining 66% of the initial PL intensity and exhibiting the smallest red shift. G2-GPNCs still exist in colloidal form with bright green fluorescence, while Ola-GPNCs and G1-GPNCs have lost their fluorescence. In addition, the waterproof performance of dendritic ammonium-based encapsulated PNCs was studied (Figure 3g ). In Ola-GPNCs , significant quenching of fluorescence within 5 hours was observed . However, G1-GPNCs and G2-GPNCs still emit green fluorescence after 48 hours of exposure . Furthermore, to examine the stability of dendritic ammonium-based encapsulated PNCs to harsh ion exchange conditions, the samples were exposed to trimethylsilyl iodide ( TMS-I ), which reacts violently with moisture in the air to generate heat and I – source of radical iodine. In Figure 3h , it was found that after adding TMS -I to the Ola-GNCs solution, the instantaneous and significant emission peak shifted from green ( 520 nm ) to red ( 651 nm ), indicating the rapid and complete conversion of Br- and I- exchange, causing the emission intensity to be reduced to 57% of the original value . As time goes by, the emission peak gradually moves from lower wavelength (red) to lower wavelength (green), and the emission intensity further decreases, which may be attributed to the I - in CsPb(Br/I) 3 NCs under harsh conditions. degradation. In contrast, G1-GPNCs also showed a transient emission peak shift from green ( 520 nm ) to red ( 600 nm ) after adding TMS-I , and then slowly moved to lower wavelength ( 533 nm ), but with Compared with Ola-GNCs , the strength decreases slowly. In the case of G2-GPNCs , the PL intensity is only reduced by 14% due to the very limited halide permeability , which results in higher retention of core components of PNCs and stable green light emission. These results confirm that the use of dendritic ligands from G1 to G2 is very beneficial for the stability of PNCs .
Point 3 : Luminescence properties of G2-BPNC and G2-RPNC
G2 ligands are also used to synthesize blue light emitting materials ( G2-BPNCs ) and red light emitting materials ( G2-RPNCs ). The photoluminescence peaks of purified PNCs are 462 nm of G2-BPNCs and 619 nm of G2-RPNCs respectively , and their photoluminescence quantum yields are 67% and 78% respectively (Figure 4a and 4b ). The fluorescence lifetime was also fitted by a double exponential function, and the average fluorescence lifetime of G2-BPNCs was 20 ns , while that of G2-RPNCs was 136 ns (Fig. 4c ). Compared with typical PNCs , G2-RPNCs have a longer lifetime of 136.4 ns . Therefore, the authors believe that in addition to the defect passivation effect, the insulating nature of G2 also contributes to the longevity because the dendritic structure can inhibit charge transfer between the ligand and the perovskite interface. The crystal structure is consistent with that typical of CsPbBr and CsPbI (Fig . 4d ). The transmission electron microscopy images of G2-BPNCs and G2-RPNCs showed uniform cubic shapes with average diameters of 17.9 and 14.7 nm , respectively , and maintained single crystal form (Figures 4e , 4f , 4i, and 4j ). EDS mapping showed a uniform distribution of lead and halogen; the halogen ratio was determined to be Br/Cl = 1.7 in G2-BPNCs and Br/I = 0.47 in G2-RPNCs (Figures 4g , 4h , 4k , and 4l ).
Figure 4 Optical, structural, morphological and compositional analysis of synthesized G2-BPNC and G2-RPNC
In order to construct an all-perovskite-based white light-emitting glass, preliminary tests were conducted on the WLED characteristics of hybrid PNCs . After mixing the two PNCs , a bright yellow emitting solution with two independent PL emissions was successfully obtained . After being stored for 48 hours , the sample still retained bright yellow luminescence, and the luminescence intensity decreased by no more than 19% , and there was no obvious peak shift. It can be seen that it has strong solvent resistance and little change in components ( Figure 5a) . The mixture of G2-GPNCs and G2-RPNCs was directly applied as phosphor to fabricate blue LED- excited perovskite-based WLEDs without any special post-processing ( Figure 5b) . The emission spectra of the prepared all-perovskite white LED are shown in Figures 5c and 5d . The emission spectra are centered at 451 , 527 and 619 nm , covering the entire visible light region, and are located at the CIE chromaticity coordinates of (0.312, 0.309) white light district. At the same time, the green and red LEDs are also made of separate G2-GPNCs and G2-RPNCs . The CIE chromaticity coordinates of the green LED are (0.0769,0.7608) and the CIE chromaticity coordinates of the red LED are (0.6707,0.3273) . Low voltage (3 V) and different operating currents were used to test the color stability of white LEDs ( Figure 5e) . When the current increases from 10 mA to 180 mA , the light intensity between the two phosphors increases steadily.
Figure 5 WLED properties of hybrid dendritic-capped PNCs
Point 4 : Design and preparation of self-powered white light-emitting glass
Based on the above findings in white LED and LSC applications, the authors designed a self-powered white light-emitting glass, as shown in Figure 6f . To simplify the device, two laminated glass plates were fabricated, one of which contained silicon photovoltaic cells for LSCs , and the collected electricity was loaded onto a 3W blue LED strip. Another glass pane serves as white emissive glass with blue LED strips on the edges and the sides are covered with reflective strips. During the day, the capped PNC LSCs will generate energy and store it, while at night, the stored energy can be used in blue LED strips and further pumped into the sealed laminated glass. Under a 1 AM solar simulator, the LSCs lit up a 0.5 m blue LED strip, and bright white light could be observed from the edge. After covering the side edges with reflective tape, bright white light is emitted from the flat surface ( Figure 6h) . The CIE chromaticity coordinates of the emission spectrum corresponding to the prepared whitish glass are (0.333, 0.324) , the high color rendering index is 94, and the CCT is 6028 K. Optical data has great potential for practical indoor lighting. After simple calculation, the energy collected by LSCs in 8 hours can power LEDs of the same area for about 147 minutes, showing the good practicality of this work.
Figure 6 Self-powered white light emitting glass device and optoelectronic characteristics
Self-powered white light glass is integrated into the building, using a standard double-glazed window structure as shown in Figure 7 . Glass containing LSC is installed on the exterior glazing, while white glass is installed on the interior glazing, with the two glass panels separated by an insulating layer. During the day, part of the sunlight can be used by the LSC to generate energy, which can be stored in batteries, and the remaining sunlight can pass through the glass without affecting indoor lighting. At night, the stored energy can be used to power white light glass for night lighting. This combined self-powered white light window structure can replace traditional lamp lighting and mimic natural lighting at night.
Figure 7 Schematic design of double-glazed windows made of self-powered white light glass during the day (left) and at night (right)
4. Summary
The authors synthesized two dendritic-structured ligands as rigid shells for the direct synthesis of dendritically wrapped PNCs with nearly uniform quantum yields . All-perovskite-based blue-excited WLEDs composed of encapsulated PNC mixtures exhibit stable color stability under various operating currents. In addition, hybrid PNCs were used as fluorescent layers embedded in laminated glass to achieve broadband absorption ( 300-700 nm ) of LSCs , which also showed obvious stability. Based on these encouraging research results, a self-powered white light glass with a high color rendering index of 94 was fabricated based on PNC- embedded laminated glass, with photovoltaic cells installed at the edges as LSCs to generate electricity, while additional blue LEDs were used to The PNC is pumped to obtain white light emission using the power generated by the LSC . This research paves the way towards the prospect of net-zero carbon emissions in urban areas.
5. References
Wang. A , Liu. J et al. Dendrimer-Encapsulated Halide Perovskite Nanocrystals for Self-Powered White Light-Emitting Glass . JACS
DOI: 10.1021/jacs.3c10657 ( 2023 )
https://pubs.acs.org/doi/10.1021/jacs.3c10657
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