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Degradation of InGaN-based LEDs: Demonstration of a recombination-dependent defect-generation process
摘要： This paper provides insights into the degradation of InGaN-based LEDs by presenting a comprehensive analysis carried out on devices having two quantum wells (QWs) with different emission wavelengths (495 nm and 405 nm). Two different configurations are considered: one with the 495 nm QW closer to the p-side and one with the 495 nm QW closer to the n-side. The original results collected within this work indicate that (i) during stress, the devices show an increase in defect-related leakage both in reverse and low-forward voltage ranges: current increases with the square-root of stress time, indicating the presence of a diffusion process; (ii) stress induces a decrease in the luminescence signal emitted by both quantum wells: the drop in luminescence is stronger when measurements are carried out at low current levels, indicating that degradation is due to the generation of Shockley–Read–Hall recombination centers; (iii) remarkably, the degradation rate is linearly dependent on the luminescence signal emitted before stress by the well, indicating that carrier density impacts on degradation; and (iv) the optical degradation rate has a linear dependence on the stress current density. The results strongly suggest the existence of a recombination-driven degradation process: the possible role of Shockley–Read–Hall and Auger recombination is discussed. The properties of the defects involved in the degradation process are described through steady-state photocapacitance measurements.
关键词： quantum wells,Shockley–Read–Hall recombination,Auger recombination,degradation,steady-state photocapacitance,InGaN-based LEDs
更新于2025-09-23 15:21:01
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Reduced-dimensional perovskite photovoltaics with homogeneous energy landscape
摘要： Reduced-dimensional (quasi-2D) perovskite materials are widely applied for perovskite photovoltaics due to their remarkable environmental stability. However, their device performance still lags far behind traditional three dimensional perovskites, particularly high open circuit voltage (Voc) loss. Here, inhomogeneous energy landscape is pointed out to be the sole reason, which introduces extra energy loss, creates band tail states and inhibits minority carrier transport. We thus propose to form homogeneous energy landscape to overcome the problem. A synergistic approach is conceived, by taking advantage of material structure and crystallization kinetic engineering. Accordingly, with the help of density functional theory guided material design, (aminomethyl) piperidinium quasi-2D perovskites are selected. The lowest energy distribution and homogeneous energy landscape are achieved through carefully regulating their crystallization kinetics. We conclude that homogeneous energy landscape significantly reduces the Shockley-Read-Hall recombination and suppresses the quasi-Fermi level splitting, which is crucial to achieve high Voc.
关键词： homogeneous energy landscape,open circuit voltage loss,Reduced-dimensional perovskite,photovoltaics,Shockley-Read-Hall recombination
更新于2025-09-19 17:13:59
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Reconstructing charge-carrier dynamics in porous silicon membranes from time-resolved interferometric measurements
摘要： We performed interferometric time-resolved simultaneous reflectance and transmittance measurements to investigate the carrier dynamics in pump-probe experiments on thin porous silicon membranes. The experimental data was analysed by using a method built on the Wentzel-Kramers-Brillouin approximation and the Drude model, allowing us to reconstruct the excited carriers’ non-uniform distribution in space and its evolution in time. The analysis revealed that the carrier dynamics in porous silicon, with ~50% porosity and native oxide chemistry, is governed by the Shockley-Read-Hall recombination process with a characteristic time constant of 375 picoseconds, whereas diffusion makes an insignificant contribution as it is suppressed by the high rate of scattering.
关键词： carrier dynamics,porous silicon,Drude model,Shockley-Read-Hall recombination,interferometric measurements
更新于2025-09-11 14:15:04