Suspended photonic crystal membranes in AlGaAs heterostructures for integrated multi-element optomechanics

We present high-reflectivity mechanical resonators fabricated from AlGaAs heterostructures for use in free-space optical cavities operating in the telecom wavelength regime. The mechanical resonators are fabricated in slabs of GaAs and patterned with a photonic crystal to increase their out-of-plane reflectivity. Characterization of the mechanical modes reveals residual tensile stress in the GaAs device layer. This stress results in higher mechanical frequencies than in unstressed GaAs and can be used for strain engineering of mechanical dissipation. Simultaneously, we find that the finite waist of the incident optical beam leads to a dip in the reflectance spectrum. This feature originates from coupling to a guided resonance of the photonic crystal, an effect that must be taken into account when designing slabs of finite size. The single- and sub-\upmum-spaced double-layer slabs demonstrated here can be directly fabricated on top of a distributed Bragg reflector mirror in the same material platform. Such a platform opens a route for realizing integrated multi-element cavity optomechanical devices and optomechanical microcavities on chip.Comment: close to published version, 4+9 pages, 6+11 figure

Perovskite Light Emitting Diode Characteristics: The Effects of Electroluminescence Transient and Hysteresis

The reproducibility of results is one of the corner stones of scientific research. However, in emerging technologies, the reported results often tend to be sensitive to the chosen measurement protocol. This can stem from measurement artifacts or from unknown complex underlying phenomena. Metal halide perovskites have emerged as an exciting material system for optoelectronic devices. The anomalous hysteresis in the current density-voltage (J-V) characteristics of perovskite solar cells has triggered wide discussions on how to report their power conversion efficiency (PCE) to achieve consistency between different research groups. However, less attention is so far given to the anomalous effects that can affect the reporting of the characteristics of perovskite light emitting diodes (PeLEDs). Here, we show that even for PeLEDs with little J-V hysteresis, the transient response and hysteresis of electroluminescence (EL), likely caused by ion migration, heat accumulation and device degradation under electrical excitation, can lead to significantly different device characteristics depending on the measurement procedures for the same device. Therefore, we propose a method based on pulsed excitation that allows better reproducibility and interpretation of the measured device characteristics. Furthermore, we also provide suggestions on reporting PeLED characteristics, as input for further discussions in the scientific community.status: publishe

Suspended photonic crystal membranes in AlGaAs heterostructures for integrated multi-element optomechanics

status: publishe

Minimizing the Interface-Driven Losses in Inverted Perovskite Solar Cells and Modules

The inverted p-i-n perovskite solar cells hold high promise for scale-up toward commercialization. However, the interfaces between the perovskite and the charge transport layers contribute to major power conversion efficiency (PCE) loss and instability. Here, we use a single material of 2-thiopheneethylammonium chloride (TEACl) to molecularly engineer both the interface between the perovskite and fullerene-C60 electron transport layer and the buried interface between the perovskite and NiOx-based hole transport layer. The dual interface modification results in optimized band alignment, suppressed nonradiative recombination, and improved interfacial contact. A PCE of 24.3% is demonstrated, with open-circuit voltage (Voc) and fill factor (FF) of 1.17 V and 84.6%, respectively. The unencapsulated device retains &gt;97.0% of the initial performance after 1000 h of maximum power point tracking under illumination. Moreover, a PCE of 22.6% and a remarkable FF of 82.4% are obtained for a mini-module with an active area of 3.63</p