3.2 Gigabit-per-second Visible Light Communication Link with InGaN/GaN MQW Micro-photodetector.

This paper presents the first demonstration of InGaN multiple quantum well (MQW) based micro-photodetectors (µPD) used as the optical receiver in orthogonal frequency-division multiplexing (OFDM) modulated visible communication system (VLC). The 80-µm diameter µPD exhibits a wavelength-selective responsivity in the near-UV to violet regime (374 nm - 408 nm) under a low reverse bias of -3 V. The modulation scheme of 16-quadrature amplitude modulation (16-QAM) OFDM enables the use of frequency response beyond -3 dB cutoff bandwidth of µPD. A record high data rate of 3.2 Gigabit per second (Gpbs) was achieved as a result, which provides the proof-of-concept verification of a viable high speed VLC link.

Ultralow Self-Doping in Two-dimensional Hybrid Perovskite Single Crystals.

Unintentional self-doping in semiconductors through shallow defects is detrimental to optoelectronic device performance. It adversely affects junction properties and it introduces electronic noise. This is especially acute for solution-processed semiconductors, including hybrid perovskites, which are usually high in defects due to rapid crystallization. Here, we uncover extremely low self-doping concentrations in single crystals of the two-dimensional perovskites (C6H5C2H4NH3)2PbI4·(CH3NH3PbI3)n-1 (n = 1, 2, and 3), over three orders of magnitude lower than those of typical three-dimensional hybrid perovskites, by analyzing their conductivity behavior. We propose that crystallization of hybrid perovskites containing large organic cations suppresses defect formation and thus favors a low self-doping level. To exemplify the benefits of this effect, we demonstrate extraordinarily high light-detectivity (1013 Jones) in (C6H5C2H4NH3)2PbI4·(CH3NH3PbI3)n-1 photoconductors due to the reduced electronic noise, which makes them particularly attractive for the detection of weak light signals. Furthermore, the low self-doping concentration reduces the equilibrium charge carrier concentration in (C6H5C2H4NH3)2PbI4·(CH3NH3PbI3)n-1, advantageous in the design of p-i-n heterojunction solar cells by optimizing band alignment and promoting carrier depletion in the intrinsic perovskite layer, thereby enhancing charge extraction.

20-meter underwater wireless optical communication link with 1.5 Gbps data rate.

The video streaming, data transmission, and remote control in underwater call for high speed (Gbps) communication link with a long channel length (~10 meters). We present a compact and low power consumption underwater wireless optical communication (UWOC) system utilizing a 450-nm laser diode (LD) and a Si avalanche photodetector. With the LD operating at a driving current of 80 mA with an optical power of 51.3 mW, we demonstrated a high-speed UWOC link offering a data rate up to 2 Gbps over a 12-meter-long, and 1.5 Gbps over a record 20-meter-long underwater channel. The measured bit-error rate (BER) are 2.8 × 10-5, and 3.0 × 10-3, respectively, which pass well the forward error correction (FEC) criterion.

Layer-edge device of two-dimensional hybrid perovskites.

Two dimensional layered organic-inorganic hybrid perovskites (2D perovskites) are potential candidates for next generation photovoltaic device. Especially, the out-of-plane surface perpendicular to the superlattice plane of 2D perovskites (layer-edge surface) has presented several exotic behaviors, such as layer-edge states which are found to be crucial for improving the efficiency of 2D perovskite solar cells. However, fundamental research on transport properties of layer-edge surface is still absent. In this report, we observe the electronic and opto-electronic behavior in layer-edge device of 2D perovskites. The dark and photo currents are demonstrated to strongly depend on the crystallographic orientation in layer-edge device, and such anisotropic properties, together with photo response, are related to the thickness of inorganic layers. Finally, due to the abundant hydroxyl groups, water molecules are easy to condense on the layer-edge surface, and the conductance is extremely sensitive to the humidity environment, indicating a potential application of humidity sensor.

Surface Effect on 2D Hybrid Perovskite Crystals: Perovskites Using an Ethanolamine Organic Layer as an Example.

Despite the remarkable progress of optoelectronic devices based on hybrid perovskites, there are significant drawbacks, which have largely hindered their development as an alternative of silicon. For instance, hybrid perovskites are well-known to suffer from moisture instability which leads to surface degradation. Nonetheless, the dependence of the surface effect on the moisture stability and optoelectronic properties of hybrid perovskites has not been fully investigated. In this work, the influence of the surface effect of 2D layered perovskites before and after mechanical exfoliation, representing rough and smooth surfaces of perovskite crystals, are studied. It is found that the smooth 2D perovskite is less sensitive to ambient moisture and exhibits a considerably low dark current, which outperforms the rough perovskites by 23.6 times in terms of photodetectivity. The superior moisture stability of the smooth perovskites over the rough perovskites is demonstrated. Additionally, ethanolamine is employed as an organic linker of the 2D layered perovskite, which further improves the moisture stability. This work reveals the strong dependence of the surface conditions of 2D hybrid perovskite crystals on their moisture stability and optoelectronic properties, which are of utmost importance to the design of practical optoelectronic devices based on hybrid perovskite crystals.

A Self-Powered and Flexible Organometallic Halide Perovskite Photodetector with Very High Detectivity.

Flexible and self-powered photodetectors (PDs) are highly desirable for applications in image sensing, smart building, and optical communications. In this paper, a self-powered and flexible PD based on the methylammonium lead iodide (CH3 NH3 PBI3 ) perovskite is demonstrated. Such a self-powered PD can operate even with irregular motion such as human finger tapping, which enables it to work without a bulky external power source. In addition, with high-quality CH3 NH3 PBI3 perovskite thin film fabricated with solvent engineering, the PD exhibits an impressive detectivity of 1.22 × 1013 Jones. In the self-powered voltage detection mode, it achieves a large responsivity of up to 79.4 V mW-1 cm-2 and a voltage response of up to ≈90%. Moreover, as the PD is made of flexible and transparent polymer films, it can operate under bending and functions at 360 ° of illumination. As a result, the self-powered, flexible, 360 ° omnidirectional perovskite PD, featuring high detectivity and responsivity along with real-world sensing capability, suggests a new direction for next-generation optical communications, sensing, and imaging applications.

Solution-Grown Monocrystalline Hybrid Perovskite Films for Hole-Transporter-Free Solar Cells.

High-quality perovskite monocrystalline films are successfully grown through cavitation-triggered asymmetric crystallization. These films enable a simple cell structure, ITO/CH3 NH3 PbBr3 /Au, with near 100% internal quantum efficiency, promising power conversion efficiencies (PCEs) >5%, and superior stability for prototype cells. Furthermore, the monocrystalline devices using a hole-transporter-free structure yield PCEs ≈6.5%, the highest among other similar-structured CH3 NH3 PbBr3 solar cells to date.