Control of positive and negative photo- and thermal-responses in a single PbI2@CH3NH3PbI3 micro/nanowire-based device for real-time sensing, nonvolatile memory, and logic operation

CH3NH3PbI3 has shown great potential for photodetectors and photovoltaic devices due to its excellent positive response to visible light. However, its real-time response characteristics hinder its application in optical memory and logic operation; moreover, the presence of excessive PbI2 is a double-edged sword. Herein, we constructed a dual-terminal device using a single CH3NH3PbI3 micro/nanowire with two Ag electrodes, and then in situ introduced PbI2 quantum dots (QDs) as hole trap centres by thermal decomposition at 160 °C. An anomalous negative photoconductivity (NPC) effect for sub-bandgap light below the PbI2 bandgap is obtained. Importantly, an electrically erasable nonvolatile photomemory can be realized. Furthermore, the device also exhibits an abnormal positive thermal resistance (PTR)-related thermomemory effect, and the thermal-induced high-resistance state (HRS) can be erased by a large bias or an illumination of 365 nm super-bandgap UV light. Additionally, logical "OR" gate operations are achieved through a combination of 650 nm sub-bandgap light and a 70 °C temperature-induced HRS, as well as a large bias and 365 nm super-bandgap light-triggered low-resistance state. These effects are attributed to the excitation and injection of holes in QDs and structural defect traps. This multifunctional device, integrating real-time sensing, nonvolatile memory, and logical operation, holds significant potential for novel electronic and optoelectronic applications.

Highly efficient green emission Cs4PbBr6 quantum dots with stable water endurance

To date, quantum dots (QDs) based on perovskite materials with high photoluminescence quantum yield (PLQY) and stability have rarely been reported. In this work, Cs₄PbBr₆ QDs glass ceramic with high PLQY and water stability is obtained, and the research results confirm that the strong green emission originates from the trapping of free excitons by internal Br vacancies. The rise of Br vacancies and the spontaneous growth of multi-morphology Cs₄PbBr₆ QDs under the influence of air humidity increase the PLQY to 89.62%. Compared with pure QDs, the Cs₄PbBr₆ QDs maintain high-intensity luminescence after being immersed in water for up to 150 days. In short, this paper puts forward a new, to the best of our knowledge, and valuable perspective for investigating the luminescence of Cs₄PbBr₆ QDs glass ceramic derived from related work.

Different photocurrent response of Cs4PbBr6 particles

Zero-dimensional (0D) all-inorganic cesium lead halide perovskites, particularly Cs₄PbBr₆, have been attracting wide attention due to their excellent optical properties and stability. The research also focuses on the origin of green emission from Cs₄PbBr₆, which has a bandgap located in the ultraviolet B (UVB) region. So far, both Cs₄PbBr₆ without visible emission and with green emission have been successfully prepared; however, the origin of green emission remains controversial. Photocurrent response is one of the effective approaches to explore how the photo-excited carriers influence the photo-physical properties of materials. In our study, Cs₄PbBr₆ particles without visible emission and with green emission were synthesized and their photocurrent response was investigated. The former showed a positive photocurrent response, while the latter showed a negative photocurrent response. The negative response was believed to be due to a built-in electric field constructed by the charged excitons in green-emissive Cs₄PbBr₆. From our calculations, numerous vacancies of Br are easier to appear in green-emissive Cs₄PbBr₆ lattices, which could combine the neutral excitons to form charged excitons. This work may contribute to the explanation of the origin of green emission of Cs₄PbBr₆ to some extent.

Dark Self-Healing-Mediated Negative Photoconductivity of a Lead-Free Cs3Bi2Cl9 Perovskite Single Crystal

Recently, halide perovskites have emerged as a promising material for device applications. Lead-based perovskites have been widely explored, while investigation of the optical properties of lead-free perovskites remains limited. Lead-halide perovskite single crystals have shown light-induced positive photoconductivity, and as lead-free perovskites are optically active, they are expected to demonstrate similar properties. However, we report here light-induced negative photoconductivity with slow recovery in lead-free Cs₃Bi₂Cl₉ perovskite. Femtosecond transient reflectance (fs-TR) spectroscopy studies further reveal that these electronic transport properties are due to the formation of light-activated metastable trap states within the perovskite crystal. The figure of merits were calculated for Cs₃Bi₂Cl₉ single-crystal detectors, including responsivity (17 mA/W), detectivity (6.23 × 10¹¹ Jones), and the ratio of current in dark to light (∼7160). These observations for Cs₃Bi₂Cl₉ single crystals, which were optically active but showed retroactive photocurrent on irradiation, remain unique for such materials.