Aaesha Alnuaimi

Electric-field and temperature dependence of the activation energy associated with gate induced drain leakage

We examined the effect of temperature and electric field on the activation energy (Ea) of gate-induced drain leakage (GIDL) of a MOSFET. The measured GIDL current shows a temperature dependence consistent with a non-tunneling mechanism. In the low-electric-field regime and for temperatures above 55 °C, Ea is about 0.4 eV and drops from 0.4 eV to 0.1 eV as the applied gate voltage goes below VFB in the accumulation direction (decreased for the n-channel MOSFET). This suggests that electron-hole-pair generation at Si/SiO2 interface traps (Dit), enhanced by the electric field (the Poole-Frenkel effect), dominates GIDL in that regime. For temperatures below 55 °C, Ea is less than 0.15 eV for both weak and strong electric fields and displays minimal temperature dependence, indicating inelastic trap-assisted tunneling or phonon-assisted tunneling from a trap. In the very strong-electric-field regime (>1 MV/cm), band-to-band tunneling is the dominant mechanism.

Efficiency enhancement in thin-film c-Si HIT solar cells using luminescent 2.85 nm silicon nanoparticles

A simple and low-cost method for enhancing the efficiency of c-Si HIT solar cells is reported. By coating 2.85 nm silicon nanoparticles (Si NPs) on the top of the solar cells, efficiency improvement is observed with respect to the uncoated reference cells. The efficiency enhancement can be attributed to the Si NPs photoluminescence (Ultra Violet absorption followed by red re-emission). Spin coating technique was used to integrate Si NPs on the cells. Compared to uncoated solar cells, Si NPs coated solar cells show an average improvement of 2.33% and 5.16% in short circuit current density (Jsc) and efficiency respectively.

Toward fast growth of large area high quality graphene using a cold-wall CVD reactor

In this work we provide a detailed analysis on graphene synthesis by Chemical Vapor Deposition (CVD) using a cold wall CVD reactor to achieve fast production of large area high quality graphene. Using Raman spectroscopy and mapping, the effect of growth temperature, pressure and CH4 : H2 ratio have been analyzed. The results show that graphene synthesis at high temperature results in reducing the multilayer nucleation density. At a high temperature of 1060 °C, the density of multilayer graphene was reduced by more than 50%. In addition, our analysis revealed that the chamber pressure plays a major role in reducing the multilayer region formation and controlling the grain size of graphene. At 15 mbar, high quality graphene with a large grain size greater than 5 μm is achieved. Moreover, the hydrogen to methane ratio has a significant role in determining the morphology and the size of graphene domains. Our analysis provide guidelines toward the synthesis of high quality graphene using 4′′ cold wall CVD reactor that are beneficial for the large scale production of graphene.

Improved efficiency of thin film a-Si:H solar cells with Au nanoparticles

In this work, the effect of Au nanoparticles on the performance of a-Si:H solar cells is investigated experimentally. Au nanoparticles of 10, 20, 50, 80, 100, 200 and 400 nm are spin coated on ITO before metallization. The results show an increase in the Jsc and efficiency with increasing nanoparticle size. The Jsc increases from 9.34 mA/cm2 to 10.1 mA/cm2. In addition, the efficiency increases from 4.28% to 5.01%.

Enhancement in c-Si solar cells using 16 nm InN nanoparticles

In this work, 16 nm indium nitride (InN) nanoparticles (NPs) are used to increase the performance of thin-film c-Si HIT solar cells. InN NPs were spin-coated on top of an ITO layer of c-Si HIT solar cells. The c-Si HIT cell is a stack of 2 μm p type c-Si, 4–5 nm n type a-Si, 15 nm n+ type a-Si and 80 nm ITO grown on a p+ type Si substrate. On average, short circuit current density (Jsc) increases from 19.64 mA cm−2 to 21.54 mA cm−2 with a relative improvement of 9.67% and efficiency increases from 6.09% to 7.09% with a relative improvement of 16.42% due to the presence of InN NPs. Reflectance and internal/external quantum efficiency (IQE/EQE) of the devices were also measured. Peak EQE was found to increase from 74.1% to 81.3% and peak IQE increased from 93% to 98.6% for InN NPs coated c-Si HIT cells. Lower reflection of light due to light scattering is responsible for performance enhancement between 400–620 nm while downshifted photons are responsible for performance enhancement from 620 nm onwards.

Performance of planar heterojunction perovskite solar cells under light concentration

In this work, we present 2D simulation of planar heterojunction perovskite solar cells under high concentration using physics-based TCAD. The performance of planar perovskite heterojunction solar cells is examined up to 1000 suns. We analyze the effect of HTM mobility and band structure, surface recombination velocities at interfaces and the effect of series resistance under concentrated light. The simulation results revealed that the low mobility of HTM material limits the improvement in power conversation efficiency of perovskite solar cells under concentration. In addition, large band offset at perovskite/HTM interface contributes to the high series resistance. Moreover, losses due to high surface recombination at interfaces and the high series resistance deteriorate significantly the performance of perovskite solar cells under concentration.

∼23% increase in efficiency of 100 nm thin film a-si solar cells using combination of Si/InN and Au nanoparticles

In this work we report 23% increase in efficiency of n-i-p a-Si:H cells using Si, InN and Au nanoparticles. These cells shows an average improvement of 24.54% in short circuit current. The coated cells also reduce the reflection by 2.7% compared to reference cell between 300-800 nm, which indicates light is getting scattered by these nanoparticles. EQE and IQE analysis show that the overall enhancement can be attributed to photon energy downshifting with a reduction in reflectivity.

Effect of carbon diffusion on performance of thin film c-Si HIT solar cells with a-SiC passivation layer

The effect of carbon diffusion on the performance of c-Si HIT cells with aSi_1-xC_x:H passivation layer is studied. Two HIT cells are fabricated, one with a-Si passivation layer and one with a-SiC layer. SIMS is used to quantify the carbon diffusion into cSi. The results show a significant amount of carbon at the interface and in the c-Si layer. With the carbon diffusion, the V_oc, J_sc and fill factor drop from 0.523V to 0.331V, 24 mA/cm² to 21 mA/cm² and from 56% to 21% respectively. In addition, the peak EQE drops by 4%. The dark current increases from 6.24×10^-4 mA/cm² to 3.50×10^-3 mA/cm² at V=-0.5V. Moreover, the results indicate that the carbon diffusion reduces the overall c-Si lifetime in addition to increasing the amount of D_it at the interface.

ITO, Si3N4 and ZnO:Al -- Simulation of Different Anti-reflection Coatings (ARC) for Thin Film a-Si:H Solar Cells

For thin film solar cells incorporating amorphous silicon (a-Si:H) as absorber materials, minimizing reflection from the top surface i.e. maximizing transmittance of the incoming light into the absorber for higher absorption plays an important role for the overall device performance. This paper discusses ways to minimize reflection using different anti-reflection coatings (ARC) at the top surface of the solar cell. Focus of this paper is to study the effect of ITO, Si3N4 and ZnO:Al as ARC on thin film aSi:H n-i-p solar cells. The influences of electrical and optical properties of the said materials are modeled using Sentaurus TCAD. Results suggest that 60 nm Si3N4 proves to be the best ARC among the studied three and a very thin layer of ZnO:Al e.g. 20 nm can also be effective.

∼10% increase in short-circuit current density using 100nm plasmonic Au nanoparticles on thin film n-i-p a-Si:H solar cells

The effect of Au nanoparticles on the performance of a-Si:H solar cells is investigated experimentally. 100 nm colloidal plasmonic Au nanoparticles are spin-coated before metallization on a-Si:H n-i-p solar cells with 100 nm thick intrinsic absorber layer. The Jsc increases from 5.91 mA/cm2 to 6.5 mA/cm2 (10% increase) and the peak EQE increases from 45% to 51% (13.3% increase) for the 100 nm i-layer solar cell after plasmonic enhancement. In addition the effect of i-layer thickness on the amount of plasmonic enhancement is studied. For the 500 nm i-layer cell, the Jsc increases from 9.34 mA/cm2 to 10.1 mA/cm2 (7.5% increase). The results show that plasmonic enhancement is more effective for thinner a-Si:H solar cells.