Silicon quantum dots (SiQDs) have emerged as a promising material for light-emitting diodes (LEDs) and display technologies due to their tunable bandgap, compatibility with existing silicon-based fabrication processes, and potential for high-efficiency electroluminescence. Unlike bulk silicon, which is an indirect bandgap material with poor light emission properties, SiQDs exhibit quantum confinement effects that enable efficient photoluminescence and electroluminescence. This article explores the application of SiQDs in LEDs and displays, focusing on device architectures, charge injection optimization, and strategies to overcome key challenges such as Auger recombination and electrical instability.

One of the most significant advantages of SiQDs is their size-dependent emission properties. By controlling the diameter of the quantum dots, the bandgap can be tuned to emit light across the visible spectrum, from blue to red. This tunability is critical for full-color displays, where precise control over emission wavelengths is required. For example, SiQDs with diameters around 2 nm emit blue light, while larger dots around 5 nm emit red light. This size-dependent emission has been leveraged to demonstrate prototypes of SiQD-based LEDs capable of covering a broad color gamut.

To achieve efficient electroluminescence, researchers have explored various device architectures. A common approach involves embedding SiQDs in a host matrix, such as an organic semiconductor or a metal oxide, to facilitate charge transport and injection. Hybrid organic-inorganic structures have shown particular promise, where SiQDs are combined with conductive polymers or small-molecule organic materials. These hybrid structures benefit from the high carrier mobility of organic materials while maintaining the robust optical properties of SiQDs. For instance, devices using poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a hole-transport layer and SiQDs as the emissive layer have demonstrated external quantum efficiencies (EQEs) exceeding 5%.

Charge injection optimization is another critical factor in improving the performance of SiQD-based LEDs. Efficient injection of both electrons and holes into the quantum dots is necessary to achieve high electroluminescence efficiency. However, the large energy barriers between the electrodes and the SiQDs can hinder charge injection. To address this, researchers have employed interfacial engineering techniques, such as introducing thin interlayers of metal oxides or organic materials to reduce energy barriers. For example, zinc oxide (ZnO) nanoparticles have been used as an electron-transport layer due to their high electron affinity, which aligns well with the conduction band of SiQDs. Similarly, nickel oxide (NiO) has been used as a hole-injection layer to improve hole transport.

Despite these advances, several challenges remain in the development of SiQD-based LEDs. One major limitation is Auger recombination, a non-radiative process where an electron-hole pair recombines without emitting light, transferring energy to a third carrier instead. Auger recombination becomes more pronounced at high carrier densities, which are typical in LED operation. This process significantly reduces the luminescence efficiency and can lead to device degradation over time. Strategies to mitigate Auger recombination include reducing the size dispersion of SiQDs, passivating surface defects with ligands, and engineering the device to operate at lower current densities.

Electrical instability is another challenge that affects the long-term performance of SiQD-based LEDs. The presence of surface defects and dangling bonds on SiQDs can trap charges, leading to uneven charge distribution and reduced efficiency. Surface passivation with organic ligands or inorganic shells has been shown to improve stability by reducing defect states. For example, hydrogen-terminated SiQDs exhibit higher stability compared to those with oxide surfaces, but they are susceptible to oxidation under ambient conditions. To enhance stability, researchers have explored more robust passivation methods, such as using alkyl ligands or encapsulating SiQDs in protective matrices.

Progress in achieving full-color emission with SiQDs has been notable. By carefully controlling the size distribution and surface chemistry of SiQDs, researchers have demonstrated LEDs that emit pure red, green, and blue light. Combining these primary colors enables the creation of white-light-emitting devices with high color rendering indices. For instance, a hybrid device incorporating red-, green-, and blue-emitting SiQDs achieved a white-light emission with a correlated color temperature of 4500 K and a color rendering index above 80. Such advancements highlight the potential of SiQDs for next-generation displays and solid-state lighting.

High external quantum efficiency is a key metric for evaluating the performance of SiQD-based LEDs. Recent studies have reported EQEs ranging from 1% to 8%, depending on the device architecture and material properties. While these values are lower than those achieved with traditional III-V semiconductor quantum dots, ongoing research aims to bridge this gap. Improvements in charge balance, reduction of non-radiative recombination pathways, and optimization of light extraction techniques are expected to further enhance EQEs in the future.

In summary, silicon quantum dots offer a compelling platform for developing efficient and tunable LEDs and displays. Advances in device architectures, charge injection optimization, and surface passivation have enabled significant progress in achieving full-color emission and high external quantum efficiency. However, challenges such as Auger recombination and electrical instability must be addressed to unlock the full potential of SiQDs in commercial applications. Continued research into material engineering and device physics will be essential to overcome these limitations and pave the way for the widespread adoption of SiQD-based optoelectronic devices.