ACS Photonics最新文献

Perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for high-speed data-driven illumination sources in optical communication, but the mechanisms influencing the modulation speed of PeLEDs are rarely discussed. Although it has been reported to increase the modulation bandwidth by reducing the device area, this is often geometrically limited and reduces the luminous efficiency. Here, with the surface treatment of 3-trifluoromethyl-benzylammonium iodide (3-TFBzAI) in different solvents, we can create a passivation/insulating layer on perovskites to promote/decrease the efficiency and modulation speed of PeLEDs. Based on devices with different surface treatments, an equivalent circuit model to affect the modulation speed of a PeLED is constructed using impedance analysis. The optimal post-treatment with chlorobenzene/isopropanol (CB/IPA) mixed solvent not only facilitates the luminous efficiency through efficient recrystallization and surface passivation but also, more importantly, boosts the modulation speed through favored charge injection and reduced parasitic capacitance. In particular, this improvement is more pronounced in small-area devices; up to a 77.6% increment of 3 dB bandwidth is realized in below 0.25 mm² near-infrared PeLEDs with the resulting average external quantum efficiency of 11.67% and a 3 dB bandwidth of 1.9 MHz when the modulation speed is not affected by the active size.

Reversing near-field thermal radiation between a rotating pair of hot and cold dipolar objects has recently been theoretically reported at low temperature. We demonstrate that such a reversal between two indium antimonide (InSb) nanoparticles occurs at lower rotation frequency at room temperature under an external magnetic field. Additionally, a nearby InSb substrate significantly relaxes the requirement of high rotation by acting as a heat sink and exciting surface modes that couple with particle resonances, both of which are tuned by the magnetic field. Our results provide a critical understanding about reversing near-field heat transfer between nanostructures with reduced rotation frequency, pointing to the possibility of experimental observation of heat reversal around room temperature.

The buried interface is pivotal for enhancing both the efficiency and stability of p-i-n perovskite solar cells (PSCs). This is because carrier extraction and recombination processes can be significantly affected by the defects that tend to form on the bottom side. Herein, a dual-reaction site molecule homopiperazine-1,4-bis (2-ethanesulfonic acid) (HEA) is employed as an effective multifunctional passivator for a self-assembled monolayer (SAM)/perovskite interface for the inverted PSCs. The HEA molecule has two sulfonic acid groups with double action sites, which can effectively fill the ITO vacancies unanchored by SAM and simultaneously passivate the uncoordinated Pb²⁺ defects of perovskite to form an effective molecular bridge, achieving full coverage of the substrate and orderly crystallization of perovskites. The resultant device presented satisfactory efficiencies of 25.71% (0.0982 cm²) and 24.26% (1 cm²). Our device retained 91.8% of its initial power conversion efficiency (PCE) after 1000 h of operation under 1-sun illumination in a nitrogen atmosphere. This research offers important insights into further refinement and enhancement of buried interfaces in PSCs.

Although inorganic perovskite solar cells (PSCs) have made remarkable progress, ambient instability and serious nonradiative recombination loss greatly impede their further development. Herein, we develop a novel surface reconstruction process to in situ grow a 2D inorganic perovskite capping layer on a 3D CsPbI₂Br perovskite surface via the dynamic methanol treatment and subsequent thermal annealing for simultaneously enhancing the stability and suppressing nonradiative recombination of inorganic CsPbI₂Br PSCs. The dynamic methanol treatment removes the surface defective regions of CsPbI₂Br perovskite and results in forming excessive PbI₂ on the CsPbI₂Br perovskite surface, and the subsequent thermal annealing triggers the surface reconstruction reaction of excessive PbI₂ with CsPbI₂Br that leads to in situ forming of a 2D CsPb₂I₄Br layer on the CsPbI₂Br perovskite surface, which effectively decreases the defect density and enhances the stability of CsPbI₂Br perovskite. As a result, the fabricated carbon-based CsPbI₂Br PSC displays a power conversion efficiency of 14.29%. Moreover, the CsPbI₂Br device with a 2D CsPb₂I₄Br layer displays superior stability, and the efficiency of the cell without encapsulation remains at over 90% of the original value after storing in ambient conditions for 900 h.

This study aimed to present an accurate model for small-signal response analysis that is universally applicable to GaInN/GaN-based micro-light-emitting devices (μ-LEDs) since the small-signal response analysis could lead to incorrect results when a conventional p–n (or p–i–n) junction (or depletion) theory is applied to the μ-LED structure as it is. To this end, an analytical model and an equivalent circuit were established, in which the additional undesired impact caused by the employment of the passivation layer was taken into account. To experimentally validate established models, two types of samples, i.e., ones with and others without a passivation layer, were fabricated from a single epitaxial wafer with varying chip sizes. The experimental results of impedance depicted that a metal–insulator–semiconductor capacitance (C_MIS) plays a significant role in the μ-LED structure in the aspect of small-signal response analysis, unlike that in the conventional structure. That is, the C_MIS should be considered and obtained separately. A methodology to obtain the C_MIS was suggested, which enables providing a reliable value of C_MIS in a simple way, thereby demonstrating junction capacitance, depletion width, doping profile, and built-in potential for μ-LEDs depending on the chip size. The experimental results showed that the methodology suggested in this study is very reliable. We firmly believe that the analytical model, the equivalent circuit, and the methodology presented in this study will shed light on further improvements in GaInN/GaN-based μ-LEDs.