Dongyoung Kim

University College London | UCL · Department of Electronic and Electrical Engineering

One of the requirements for strong subbandgap photon absorption in the quantum-dot intermediate-band solar cell (QD-IBSC) is the partial filling of the intermediate band. Studies have shown that the partial filling of the intermediate band can be achieved by introducing Si doping to the QDs. However, the existence of too many Si dopants leads to th...

The effect of post-growth annealing on InAs/GaAs quantum dot solar cells (QDSCs) has been studied. A significant improvement in photoemission, photocurrent density, and spectral response has been observed with post-growth annealing. The optimal anneal temperature was found to be 700 ° C, which lead to an 18% improvement in current density from 4.9...

High radiation tolerance of GaAs1-xSbx based solar cells is demonstrated for the low-intensity-low-temperature (LILT) conditions of the target planets Saturn, Jupiter, and Mars. The GaAs1-xSbx-based cells are irradiated with high energy electrons to assess the effect of harsh radiation environment on the solar cell and the response of the cell is t...

Our previous studies have shown that introducing Si doping in quantum dots (QDs) can help QD solar cells achieve higher voltage. However, this improvement came at the cost of current loss. In this work, we continue to investigate the cause of the current loss and propose a method to recover it without compromising the voltage. Photoluminescence mea...

Large-scale two-dimensional (2D) glassy-graphene thin films have been reported to share similar physical and chemical properties with pristine graphene, such as excellent flexibility, transparency and electrical conductivity. Here, we report a few-layer MoS2/glassy-graphene heterostructure and its application as transparent photodetectors. Instead...

The concept of high-efficiency, high-reliability and low-threshold electrically pumped lasers monolithically grown on silicon has attracted great attention over the past several decades, as a promising on-chip optical source for Si photonics. In this paper, we report an electrically pumped continuous-wave (CW) 1.3 µm InAs/GaAs quantum dot (QD) lase...

In this work, the influence of quantum dot (QD) position on the performance of solar cells was studied. The presence of QDs within the base regions leads to improved open circuit voltage ( V oc) from 0.73 to 0.90 V. Despite a slight reduction in short-circuit current ( J sc) due to carrier collection loss, the enhancement of the V oc of QDSCs with...

The concept of introducing an intermediate band to overcome the efficiency limit of single-bandgap solar cells was proposed by Luque and Martí in 1997. It is predicted that utilising the intermediate band for multi-photon absorption can significantly improve the photocurrent generation without accompanying output voltage loss. Amongst several appro...

Nanowires (NWs) with radial p‐i‐n junction have advantages, such as large junction area and small influence from the surface states, which can lead to highly efficient material use and good device quantum efficiency. However, it is difficult to make high‐quality core–shell NW devices, especially single NW devices. Here, the key factors during the g...

Incorporation of gold nanoparticles (AuNPs) into titanium dioxide (TiO 2) photoelectrodes has been used traditionally to increase the performance of photoelectrochemical cells (PECs) through their tailored optical properties. In contrast to larger AuNPs, previous studies have suggested that smaller AuNPs are the most catalytic or effective at incre...

The effects of direct, delta, and modulation Si QD doping on InAs/GaAs QDSCs are studied. The PL, EQE, and J-V characterisation results show a clear relationship between the doping methods and the non-radiative recombination. All doped QDSCs exhibited increase in the V-{mathbf{OC}} due to{reduced thermal coupling from QD Si doping. Delta and modula...

We report thin-film InAs/GaAs quantum dot (QD) solar cells with n-i-p+ deep junction structure and planar back reflector fabricated by epitaxial lift-off (ELO) of full 3-in wafers. External quantum efficiency measurements demonstrate twofold enhancement of the QD photocurrent in the ELO QD cell compared to the wafer-based QD cell. In the GaAs wavel...

One of the primary challenges facing quantum dot (QD)-based intermediate band solar cells is the short lifetime of charge carriers (∼1 ns). To investigate this, InAs QD/GaAs ${}_{\text{1}\hbox{--}x}$ Sb ${}_{x}$ quantum well (QW) solar cells (SCs) with a 2-nm GaAs interlayer between the QDs and QW were fabricated for x = 0, 0.08, 0.14, and 0.17, re...

This paper presents an experimental and theoretical study on the impact of doping and recombination mechanisms on quantum dot solar cells based on the InAs/GaAs system. Numerical simulations are built on a hybrid approach that includes the quantum features of the charge transfer processes between the nanostructured material and the bulk host materi...

Layered van der Waals heterostructures have attracted considerable attention recently, due to their unique properties both inherited from individual two-dimensional (2D) components and imparted from their interactions. Here, a novel few-layer MoS2/glassy-graphene heterostructure, synthesized by a layer-by-layer transfer technique, and its applicati...

Controlled and reproducible doping is essential for nanowires (NWs) to realize their functions. However, for the widely used self-catalyzed vapor-liquid-solid (VLS) growth mode, the doping mechanism is far from clear, as the participation of the nanoscale liquid phase makes the doping environment highly complex and significantly different from that...

The growth of self-catalyzed core–shell nanowires (NWs) is investigated systematically using GaAs(P) NWs. The defects in the core NW are found to be detrimental for the shell growth. These defects are effectively eliminated by introducing beryllium (Be) doping during the NW core growth and hence forming Be–Ga alloy droplets that can effectively sup...

In this work, the effect of Si doping on InAs/GaAs quantum dot solar cells with AlAs cap layers is studied. The AlAs cap layers suppress the formation of the wetting layer during quantum dot growth. This helps achieve quantum dot state filling, which is one of the requirements for strong sub-bandgap photon absorption in the quantum dot intermediate...

Nanowires (NWs) have better functionality and superior performance as compared with the traditional thin film counterparts. However, NW growth is highly complicated and the growth mechanism is far from clear, especially when it is grown by vapor-liquid-solid mode. In this work, the influences of droplet size on the growth of self-catalyzed ternary...

One of the key issues in the design and development of a satellite Photovoltaic Assembly (PVA) is the trade-off to be made between the available volume located to the PVA, its mass and the total amount of power that the solar panels have to guarantee to the spacecraft. The development of high-efficiency, flexible, lightweight solar cells is therefo...

In this work, the effect of Si doping on InAs/GaAs quantum dot solar cells with AlAs cap layers is studied. The AlAs cap layers suppress the formation of the wetting layer during quantum dot growth. This helps achieve quantum dot state filling, which is one of the requirements for strong sub-bandgap photon absorption in the quantum dot intermediate...

One of the key issues in the design and development of a satellite Photovoltaic Assembly (PVA) is the trade-off to be made between the available volume located to the PVA, its mass and the total amount of power that the solar panels have to guarantee to the spacecraft. The development of high-efficiency, flexible, lightweight solar cells is therefo...

In this work, the effect of Si doping on InAs/GaAs quantum dot solar cells with AlAs cap layers is studied. The AlAs cap layers suppress the formation of the wetting layer during quantum dot growth. This helps achieve quantum dot state filling, which is one of the requirements for strong sub-bandgap photon absorption in the quantum dot intermediate...

Self-catalyzed GaAsP nanowires (NWs) have a band gap that is capable of covering the working wavelengths from green to infrared. However, the difficulties in controlling P and the complexities of the growth of ternary NWs make it challenging to fabricate them. In this work, self-catalyzed GaAsP NWs were successfully grown on Si substrates by solid-...

The influences of droplet size on the growth of self-catalyzed ternary nanowires (NWs) were studied using GaAsP NWs. The size-induced Gibbs-Thomson (GT) effect makes the smaller catalytic droplets have lower effective supersaturations and hence slower nucleation rates than the larger ones. Large variation in droplet size thus led to the growth of N...

III-V nanowire quantum dots (NWQDs) monolithically grown on silicon substrates, combining the advantages of both one- and zero-dimensional materials, represent one of the most promising technologies for integrating advanced III-V photonic technologies on a silicon microelectronics platform. However, there are great challenges in the fabrication of...

We present a study of 1.3-μm InAs/GaAs quantum dot lasers monolithically grown on Si substrates by molecular beam epitaxy. We focused on the optimization of III-V buffer layers epitaxy grown on Si substrates, which includes the nucleation layers and the dislocation filter layers. The effect of growth temperature of GaAs nucleation layer has been in...