Farsad Imtiaz Chowdhury

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.

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.

~3-nm ZnO Nanoislands Deposition and Application in Charge Trapping Memory Grown by Single ALD Step

Low-dimensional semiconductor nanostructures are of great interest in high performance electronic and photonic devices. ZnO is considered to be a multifunctional material due to its unique properties with potential in various applications. In this work, 3-nm ZnO nanoislands are deposited by Atomic Layer Deposition (ALD) and the electronic properties are characterized by UV-Vis-NIR Spectrophotometer and X-ray Photoelectron Spectroscopy. The results show that the nanostructures show quantum confinement effects in 1D. Moreover, Metal-Oxide-Semiconductor Capacitor (MOSCAP) charge trapping memory devices with ZnO nanoislands charge storage layer are fabricated by a single ALD step and their performances are analyzed. The devices showed a large memory window at low operating voltages with excellent retention and endurance characteristics due to the additional oxygen vacancies in the nanoislands and the deep barrier for the trapped holes due to the reduction in ZnO electron affinity. The results show that the ZnO nanoislands are promising in future low power memory applications.

∼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.

Enhancement of polycrystalline silicon solar cells efficiency using indium nitride particles

In this work, we present a hybrid indium nitride particle/polycrystalline silicon solar cell based on 230 nm size indium nitride particles (InN-Ps) obtained through laser ablation. The solar cell performance measurements indicate that there is an absolute 1.5% increase (Δη) in the overall solar cell efficiency due to the presence of InN-Ps. Within the spectral range 300–1100 nm, improvements of up to 8.26% are observed in the external quantum efficiency (EQE) and increases of up to 8.75% are observed in the internal quantum efficiency (IQE) values of the corresponding solar cell. The enhancement in power performance is due to the down-shifting properties of the InN-Ps. The electrical measurements are supplemented by TEM, Raman, UV/ VIS and PL spectroscopy of the InN-Ps.

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.

Growth of ∼3-nm ZnO nano-islands using Atomic Layer Deposition

In this work, the deposition of 3-nm dispersed Zinc-Oxide (ZnO) nanoislands by thermal Atomic Layer Deposition (ALD) is demonstrated. The physical and electronic properties of the islands are studied using Atomic Force Microscopy, UV-Vis-NIR spectroscopy, and X-ray Photoelectron Spectroscopy. The results show that there is quantum confinement in 1D in the nanoislands which is manifested by the increase of the bandgap and the reduction of the electron affinity of the ZnO islands. The results are promising for the fabrication of future electronic and optoelectronic devices by single ALD step.

Improved efficiency of thin film a-Si:H solar cells using combination of silver and gold plasmonic nanoparticles

The effect of gold (Au) and Silver (Ag) nanoparticles (NPs) on a-Si:H n-i-p thin-film solar cells has been studied. 80 nm Ag and 80 nm Au NPs are spin coated on top of the fabricated cells. For the cell spin coated with only Ag NPs the Jsc changes on average from 4.53 mA/cm2 to 4.69 mA/cm2. The efficiency also changes from 2.37% to 2.41%. The cell with Ag NPs also shows an improved spectral response. Compared to reference cell, the peak EQE increases by ~4.72% at 500 nm. For the cell with both Ag and Au NPs, the Jsc increases on average from 4.53 mA/cm2 to 4.75 mA/cm2. The efficiency is 2.43%. Compared to reference cell, the peak EQE increases ~6.11% at 500 nm. Compared to Ag NPs coated cell, Ag and Au NPs coated cell shows an improvement of 1.28% and 0.82% in Jsc and efficiency respectively. This indicates that combination of nanoparticle will have stronger plasmonic effect.

∼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.

∼12% Efficiency improvement in a-Si thin-film solar cells using ALD grown 2-nm-thick ZnO nanoislands

2-nm-thick ZnO nanoislands have been grown using Atomic Layer Deposition (ALD) on the surface of n-i-p a-Si:H solar cells. With the nanoislands, an average improvement of 10.6% in short circuit current density (Jsc) and 12.05% in efficiency compared to the reference cell are achieved. Improved spectral response is obtained from ZnO nanoislands coated cell with an improvement of 4.2% and 5.25% in peak EQE and IQE respectively. The coated cell also minimizes reflection between 340-520 nm indicating light scattering ability of these nanoislands. Further analysis suggests that overall enhancement can be attributed to photon energy downshifting with a reduction in reflectivity.