Fei Zheng

Two-dimensional Ruddlesden-Popper perovskites (2D RPPs) show great potential for next-generation photovoltaics. While the vertical phase distribution in 2D RPP films has been extensively studied, the impact of lateral heterogeneity within individual grains on carrier dynamics and photovoltaic performance remains elusive. Herein, we reveal that a lateral phase gradient across the grain generates a funnel-like energy landscape, which induces detrimental carrier relaxation toward the grain center before extraction. This intragrain lateral funneling is identified as a direct and previously overlooked loss channel that affects the open-circuit voltage (V_OC). As a proof-of-concept, we show that solvent engineering can help homogenize the lateral phase distribution, leading to an enhanced V_OC and power conversion efficiency in 2D perovskite solar cells. This work highlights the critical role of subgrain-scale phase uniformity and underscores the importance of regulating lateral phase heterogeneity for high-performance 2D RPP optoelectronics.

Perovskite memristors hold great promise for neuromorphic computing and bioinspired sensing, yet their development is hindered by high operating voltages, environmental instability, and limited functional integration. Here, we report a robust memristor based on a 3D/2D halide perovskite heterostructure that overcomes these challenges. The device demonstrates ultralow switching voltages of ∼+0.18 V (SET) and ∼-0.4 V (RESET), a high ON/OFF ratio >10⁴, excellent retention (>10⁴ s), and endurance (>600 cycles) under ambient conditions. This performance stems from a synergistic "bandgap staircase and built-in electric field" mechanism at the heterointerface, which enhances field confinement for low-voltage switching while the 2D layer suppresses ion migration. Remarkably, this single platform integrates a complete neuromorphic-sensory functional chain. It emulates synaptic plasticity, achieving 90.77% accuracy in MNIST handwritten digit recognition. It also functions as a physical reservoir for temporal pattern processing, reaching perfect classification accuracy. Furthermore, it serves as an artificial nociceptor that faithfully replicates key pain perceptions such as threshold, nonadaptation, sensitization, and relaxation. With ultralow power consumption of only 36 pJ per switch, this multifunctional memristor provides a versatile hardware prototype for next-generation intelligent systems and adaptive human-machine interfaces.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole transporting layer (HTL) in two-dimensional (2D) Ruddlesden-Popper perovskite (RPP)-based solar cells (2D-PSCs) due to its simple preparation process and low cost. However, the devices based on PEDOT:PSS exhibit low efficiency and poor stability due to the number of buried interfacial defects, energy level mismatching, and corrosivity of the HTL. In this study, a guanidinium iodide (GAI)-modified PEDOT:PSS HTL was adopted to tune the crystallization of 2D RPPs, leading to the formation of 2D perovskite films with preferential crystal orientation, improved crystallinity, and suppressed defect density. The addition of GAI not only enhances the conductivity and intrinsic stability of PEDOT:PSS layers but also improves their energy level matching with those of 2D perovskite films. Upon GAI doping into PEDOT:PSS, the power conversion efficiency of 2D-PSCs increased from 13.11% to 16.04% and maintained 80% of its initial value under 65% relative humidity condition for 60 days. This work demonstrates a novel synergetic modification strategy and gives new insight into the underlying mechanism, which should lead to further improvements in the performance of 2D-PSCs and other optoelectronic devices based on 2D RPPs.

The increasing computational demands of artificial intelligence (AI) algorithms are exceeding the capabilities of conventional computing architectures, creating a strong need for novel materials and paradigms. Memristors that integrate diverse resistive switching (RS) behaviors provide a promising avenue for developing novel computing architectures. In this study, we achieve the coexistence of volatile and nonvolatile RS behaviors in quasi-2D perovskite memristor (Q-2DPM). The Q-2DPM exhibits competitive performance as a nonvolatile memory. Multiple synaptic functions have been successfully simulated on Q-2DPM, such as excitatory postsynaptic currents, paired-pulse facilitation, and long-term potentiation/depression. Furthermore, artificial neural networks using Q-2DPM synapses achieve high accuracy in MNIST image classification tasks. The Q-2DPM's inherent characteristics suitable for reservoir computing are also demonstrated through its application in a pulse-stream-based digital classification experiment, showcasing its impressive performance. The elucidation of the dual RS mechanisms within Q-2DPM provides fresh insights into memristor RS behavior and underscores the potential of achieving diverse computational units through a single device. This work paves the way for the implementation of physical neuromorphic hardware architectures and the advancement of sophisticated computational primitives, offering a significant step toward the next generation of computing technologies.

Quasi‐2D Ruddlesden–Popper perovskites (RPPs) are candidates for constructing perovskite solar cells (PSCs) with superior stability due to their tolerance to the external environment. Fully understanding the film growth mechanism and structure is crucial to further improve the performance of 2D‐PSCs while maintaining device stability. In this work, the origin of Brownian tree‐shaped dendrites formed in hot‐cast methylammonium chloride (MACl)‐doped BA₂MA_n−1Pb_nI_3n+1 (<n> = 5) quasi‐2D perovskite films are reported. Investigations based on optical, electronic, atomic force, and fluorescence microscopies reveal that the dendrites are assembled from large‐n RPPs‐dominated grains, while the nondendritic film area is composed of small‐n RPPs grains and associated with film surface pits caused by the evaporation of MACl. It is proposed that these dendrites are grown by the diffusion‐limited aggregation of the MA‐rich intermediate phase domains that initially crystallize from the precursor. The formation of these dendrites in quasi‐2D perovskite films upon MACl doping is accompanied by improved organization and crystallinity of the 2D RPPs, which benefits the photovoltaic performance. This work provides new insights into the formation mechanism of quasi‐2D perovskite films that should assist device engineering strategies to further improve the performance of 2D PSCs.

The excellent performance and stability of perovskite solar cells (PSCs) based on quasi-2D Ruddlesden–Popper perovskites (RPPs) holds promise for their commercialization. Further improvement in the performance of 2D PSCs requires a detailed understanding of the microstructure of the quasi-2D perovskite films. Based on scanning transmission electron microscopy (STEM), time-resolved photoluminescence, and transient absorption measurements, a new sandwich-like structural model is proposed to describe the phase distribution of RPPs. In contrast to the conventional gradient distribution, it is found that small-n RPPs are sandwiched between large-n RPP phase layers at the front and back sides owing to crystallization initiated from both interfaces during film formation. This sandwich-like distribution profile facilitates excitons funneling from the film interior to both surfaces for dissociation while free carriers transport via large-n channels that permeate the film to ensure efficient charge collection by the corresponding electrodes, which is favorable for high-performance photovoltaics. This discovery provides a new fundamental understanding of the operating principles of 2D PSCs and has valuable implications for the design and optimization strategies of optoelectronic devices based on quasi-2D RPPs films.

0D Cs₄PbBr₆perovskite microcrystals exhibit a radiative recombination coefficient two orders of magnitude higher than typical 3D perovskite.

Potassium (K⁺) doping has been recently discovered as an effective route to suppress hysteresis and improve the performance stability of perovskite solar cells. However, the mechanism of these K⁺ doping effects is still under debate, and rationalization of the improved performance in these perovskites is needed. Herein, the photoluminescence (PL) properties and device performance of mixed‐cation mixed‐halide perovskite are dynamically monitored with and without K⁺ doping under bias light illumination via a confocal fluorescence microscope, together with ultrafast transient absorption as well as time‐dependent and time‐resolved PL measurements. It is demonstrated that illumination is essential to trigger the passivation effect of K⁺ by forming KBr‐like compounds, leading to the elimination of interface trapping defects and suppression of mobile ion migration, thus resulting in improved power conversion efficiency and negligible current–voltage hysteresis of solar cells. This work provides novel insight into the hysteresis suppression upon K⁺ doping and highlights the significance of light illumination when using this protocol.