Renjun Guo

Quantum phenomena typically occur for low temperatures. Moreover, single‐molecule and single‐particle spectroscopy have revealed a plethora of quantum phenomena in photonics. Superfluorescence (SF) is a macroscopic quantum effect where a macroscopic ensemble of emitters become coherent above a certain excitation threshold and cooperatively emit a burst of coherent photons. Amplified spontaneous emission (ASE), on the other hand, is a collective emission process where a spontaneously emitted photon propagates inside the emitter material and induces stimulated emission. Both SF and ASE lead to a narrow peak rising out of the photoluminescence spectrum. Recently, SF at room temperature was invoked for the explanation of spectral narrowing in low‐dimensional PEA:CsPbBr ₃ under high excitation. Here, we investigate the emission characteristics of this material and clarify whether ASE or SF is responsible for the emission narrowing. We do so by testing the effect on samples processed on different substrates, thereby manipulating the optical waveguide characteristics of the stack. We show, that the narrow emission peak is suppressed for substrates with a refractive index higher than the active material. This results from the absence of waveguide modes. These findings show that ASE—not SF—is the dominant mechanism responsible for the observed spectral narrowing.

In perovskite photovoltaics, self-assembled molecules (SAMs) have demonstrated the ability to enhance interface quality, reduce charge recombination, and improve energy-level alignment. However, most symmetrical molecules for photovoltaic applications tend to self-aggregate, which hinders uniform film formation, reduces the active surface area, and limits interface contact and device efficiency. In this work, we propose a symmetry-breaking co-assembly (SBC) strategy to improve the performance of the widely employed SAM of 2-[3,6-Dimethoxy-9H-carbazol-9-yl)ethyl] phosphonic acid (MeO-2PACz) by coupling with another small conjugated molecule, dibenzo[b,d]thiophene-4-carboxylic acid (DTCA). The broken symmetry at the molecular level enables the synthesis of co-SAM layers with significantly improved uniformity and coverage. A quantitative protocol based on atomic force microscope-infrared spectroscopy (AFM-IR) has been developed to determine the surface coverage of SAM layers. When the surface coverage of co-SAM layers is maximized, the interfacial chemical reaction under electrical stress and the non-radiative recombination loss are effectively suppressed, resulting in power conversion efficiencies (PCEs) of 26.32% (certified as 25.67%) and 25.34% for areas of 0.08 cm² and 1 cm², respectively. The encapsulated device retains 93% of its initial PCE after operating at the maximum power point (MPP) for 1,150 hours, as evaluated following the ISOS-L-1 protocol. These results underscore the effectiveness of the SBC strategy in advancing perovskite photovoltaics, and the coverage-maximizing methodology may be generalized to other research domains involving SAMs.

Quantum dot (QD) superlattices offer collective optoelectronic properties distinct from disordered solids^1,2,3,4, but their integration into high-resolution display devices remains elusive because of difficulties in achieving spatially defined, structurally coherent thin films. Here we report a scalable strategy for fabricating pixelated perovskite QD (PeQD) superlattice thin-film arrays that feature in-plane long-range order, vertical confinement and precise spatial patterning. By engineering rhombic dodecahedral CsPbBr₃ nanocrystals with robust surface termination by a ligand-fluoride co-stabilization approach, we direct the formation of hexagonally close-packed superlattice films using capillary liquid-bridge confined assembly. These superlattice films exhibit reduced energetic disorder and enhanced electronic coupling. When integrated into light-emitting diodes (LEDs), the electrically driven PeQD superlattices yield an external quantum efficiency of 30.9%, high luminance of 117,144 cd m⁻² and pixel densities of up to 5,080 pixels per inch. The devices show an extrapolated operational half-lifetime (T₅₀) of 12,411 h at 100 cd m⁻²—more than 1,000-fold longer than previously reported pixelated PeQD LEDs. Moreover, we demonstrate the direct integration of patterned superlattices onto a commercial thin-film transistor backplane to construct a 1.85-inch active-matrix display with full greyscale control and video playback ability. These results establish colloidal QD superlattices as a viable material platform for next-generation high-resolution, stable and efficient perovskite displays.

Monolithic perovskite/silicon tandem photovoltaics are among the most promising high‐efficiency technologies for next‐generation photovoltaics. However, the commercial development of two‐terminal (2T) tandem configurations is limited by their operational instability of wide‐bandgap perovskite materials, which leads to current mismatch and increased sensitivity to solar spectral variations. Three‐terminal (3T) tandem architectures offer a viable route to address these limitations. Here, we demonstrate the real‐world advantages of 3T perovskite/silicon tandem solar cells in mitigating current mismatch limitations and losses arising from solar spectral variations. Our 3T tandem solar cells achieve a power conversion efficiency of 30.1%, integrating a front‐side textured interdigitated back contact (IBC) and poly‐Si on oxide contact (POLO) silicon bottom cell. This is one of the highest efficiencies reported for 3T tandem solar cells so far. Through a direct comparison of 2T and 3T tandem configurations enabled by a novel measurement framework, we reveal that 3T architectures decouple performance from perovskite bandgap constraints, alleviating the need for the current matching. Additionally, 3T tandem solar cells exhibit enhanced spectral resilience under varying solar spectra when the top cell limits the short‐circuit current. These findings underscore the potential of 3T architectures for stable and efficient tandem photovoltaics under real‐world operating conditions.

Temperature variations can induce phase transformations and strain in perovskite solar cells (PSCs), undermining their structural stability and device performance. Despite growing interest, the operational stability of triple-cation wide-bandgap (WBG) PSCs and tandem solar cells (TSCs) under rapid solar-thermal cycling remains poorly understood. Here, we investigate the operational stability of WBG PSCs (~1.68 eV) with a champion power conversion efficiency (PCE) of 24.31% and extend the study to TSCs. We find that degradation during device operation under rapid solar-thermal cycling (temperature change rate of 10 °C/min) is independent of passivation and occurs in two distinct regimes: an initial burn-in phase, which accounts for a rapid 60% relative loss in performance, followed by a steady degradation characterized by temperature-dependent fluctuations in photovoltaic parameters. By operando grazing-incidence wide-angle X-ray scattering and photoluminescence measurements, we reveal that temperature-induced strain, phase transition, and the increased non-radiative recombination collectively contribute to the degradation of PSCs. This work advances the understanding of the degradation mechanisms of WBG PSCs and TSCs, providing insights toward improving their operational thermal stability for real-world applications.

Understanding the crystallization kinetics of Br–I mixed-halide WBG perovskite films, and their correlation to the crystallographic structure and charge transfer dynamics, is critical for advancing WBG perovskite devices.

Reducing interfacial non-radiative recombination at the perovskite/electron transport layer interface remains a critical challenge for achieving high performance and stable perovskite/silicon tandem solar cells. This study analyzes energy losses and design bilayer passivation for enhancing the performance and durability of tandem solar cells. Our experimental results confirm that, the bilayer passivation strategy, precisely modulates perovskite energy level alignment, reduces defect density, and suppresses interfacial non-radiative recombination. Moreover, the ALD-AlO_x forms a homogeneous film on the perovskite grain surface while creating island-like structures at grain boundaries, enabling nanoscale local contact areas for subsequent PDAI₂ deposition. While serving as an ion diffusion barrier, this structure facilitates moderate n-type doping and enhances charge extraction and transport efficiency. Monolithic perovskite/silicon tandem solar cells incorporating AlO_x/PDAI₂ treatment achieve a power conversion efficiency of 31.6% (certified at 30.8%), utilizing industrial silicon bottom cells fabricated with Q CELLS’ Q.ANTUM technology. Furthermore, our device exhibits 95% efficiency retention after 1000 hours of maximum power point tracking at 25 ^oC.