Addressing the Voltage Induced Instability Problem of Perovskite Semiconductor Detectors

Perovskite-based solid-state radiation detectors have delivered impressive performances, but the electrical field induced instability has been a major detriment for the further development. Here, we identify the voltage-induced instability is directly tied to the humidity levels. A higher humidity elicits a hysteresis in the current–voltage curve and lowers the breakdown voltage. We further add a fluorinated phenylethylamine iodide (5F-PEAI) barrier layer on the perovskite, which protects the device against voltage damage. Photoluminescence maps identify the ion migration and degradation can be suppressed by 5F-PEAI. Quantum chemical simulations corroborate experimental results by revealing high energy barrier for water penetrating the 5F-PEAI layer with enhancing stability of halide perovskite under humid condition. Using a treated device, we demonstrate high X-ray sensitivities approaching 1000 μC/(Gyair·cm2) under high biases. Our work provides a mechanistic understanding on the voltage instability of 2D perovskite detectors and provides a viable solution toward robust detector development

Thiophene-Based Polyelectrolyte Boosts High-Performance Quasi-2D Perovskite Solar Cells with Ultralow Energy Loss

The rise of quasi-2D perovskite structures holds great promise for highly efficient and stable perovskite solar cells (PCSs). As such, fabricating large-area quasi-2D perovskite solar cells (PCSs) with high power conversion remains under active exploration. We identified that maintaining the homogeneous crystalline orientation upon scaling up is a key challenge. Thus, we introduce a thiophene-based polyelectrolyte as the hole transporting layer (HTL) to facilitate large area quasi-2D PCSs fabrication with high performance. The HTL with carboxyl acid anchoring groups can be attached to various conducting metal oxide substrates, enabling a conformal self-assembled monolayer (SAM). This SAM surface facilitates the quasi-2D perovskite crystal growth vertically aligned to the substrate. Along with a favorable energy alignment, a high open-circuit voltage (VOC) of 1.24 V was achieved, approaching the Shockley-Queisser optimal limit (VOC = 1.34 V). Remarkably, the device maintained over 80% of its initial efficiency after operating at the maximum power point under simulated AM1.5G solar irradiation for 1000 h at a relative humidity of 60%. These findings offer new fabrication strategies, paving the way to scalable quasi-2D PCS production with high efficiencies

Nitrogen-Embedded Quintuple [7]Helicene: A Helicene–Azacorannulene Hybrid with Strong Near-Infrared Fluorescence

Herein, a nitrogen-embedded quintuple [7]­helicene (N-Q7H) with an azapentabenzocorannulene core, which can be considered to be a helicene/azacorannulene hybrid π-system, was synthesized from azapentabenzocorannulene in a three-step process. N-Q7H is the first example of a multiple helicene with an azabuckybowl core. Single-crystal X-ray diffractometry unambiguously confirmed the structure of the propeller-shaped hybrid π-system. Owing to nitrogen-atom doping in the multiple helicenes and effective hybridization between the helicene and azacorannulene, N-Q7H exhibits considerably redshifted absorption and emission (yellow-to-green color change and green-to-near-infrared fluorescence change) relative to the azapentabenzocorannulene core. The broad absorption from the ultraviolet–visible to the NIR region is ascribable to the allowed transition between the highest occupied molecular orbital and the lowest unoccupied molecular orbital after symmetry breaking, as revealed by density functional theory calculations. Compared to previous propeller-shaped multiple helicenes with corannulene or hexabenzocoronene (etc.) as cores, N-Q7H demonstrates a significantly higher NIR fluorescence quantum efficiency of 28%. Additionally, the chiral-resolution and redox properties of N-Q7H were investigated. The excellent photophysical and inherent chiral properties of N-Q7H suggest that azapentabenzocorannulene can be used as an outstanding nitrogen-embedded core to construct novel multiple helicenes with wide application potential, including as NIR fluorescent bio-probes