Publications de Ali Naqavi | EPFL Graph Search

Self-Assembled Monolayer of Wavelength-Scale Core-Shell Particles for Low-Loss Plasmonic and Broadband Light Trapping in Solar Cells

Scattering particles constitute a key light trapping solution for thin film photovoltaics where either the particles are embedded in the light absorbing layer or a thick layer of them is used as a reflector. Here we introduce a monolayer of wavelength-scal ...

Amer Chemical Soc2016

Intensity and phase fields behind phase-shifting masks studied with high-resolution interference microscopy

Hans Peter Herzig, Myun Sik Kim, Toralf Scharf, Ali Naqavi, Krishnaparvathy Puthankovilakam

We try to find out the details of how light fields behind the structures of photomasks develop in order to determine the best conditions and designs for proximity printing. The parameters that we use approach real situations like structure printing at prox ...

SPIE-Intl Soc Optical Eng2016

Super-Lambertian photocurrent-generation in solar cells with periodically textured interfaces

Christophe Ballif, Karin Söderström, Franz-Josef Haug, Ali Naqavi

We studied solar cells with periodic interface texture. For periods of 550 and 833 nm, we found that the measured photocurrent increases under oblique incidence and assumes a maximum between 20 and 30°. For the geometries used in our experiments, the initi ...

American Institute of Physics2013

Light trapping in solar cells at the extreme coupling limit

Christophe Ballif, Hans Peter Herzig, Franz-Josef Haug, Ali Naqavi, Corsin Battaglia

We calculate the maximal absorption enhancement obtainable by guided mode excitation in a weakly absorbing dielectric slab over wide wavelength ranges. The slab mimics thin film silicon solar cells in the low absorption regime. We consider simultaneously w ...

Optical Soc Amer2013

Limit of light coupling strength in solar cells

Christophe Ballif, Hans Peter Herzig, Toralf Scharf, Franz-Josef Haug, Ali Naqavi

We introduce a limit for the strength of coupling light into the modes of solar cells. This limit depends on both a cell’s thickness and its modal properties. For a cell with refractive index n and thickness d, we obtain a maximal coupling rate of $2c\sqrt ...

American Institute of Physics2013

Plasmonic silicon solar cells: impact of material quality and geometry

Christophe Ballif, Céline Pahud, Hans Peter Herzig, Franz-Josef Haug, Ali Naqavi

We study n-i-p amorphous silicon solar cells with light-scattering nanoparticles in the back reflector. In one configuration, the particles are fully embedded in the zinc oxide buffer layer; In a second configuration, the particles are placed between the b ...

Optical Society of America2013

Absorption enhancement in thin-film silicon solar cells

Ali Naqavi

Thin-film silicon technology is a major candidate to comply with the ever-increasing global energy demand. The small thickness of silicon allows high industrial throughput and low material usage and subsequently opens new avenues to mass-production of low- ...

EPFL2013

Geometrical Impact on Guided Mode Excitation in Solar Cells

Christophe Ballif, Hans Peter Herzig, Karin Söderström, Franz-Josef Haug, Ali Naqavi

We investigate the influence of patterned metallic back reflector on absorption in thinfilm silicon photovoltaics. The impact of symmetry, periodicity, and angle of incidence of light is discussed by simulation and experiment. ...

2012

Diffraction and absorption enhancement from textured back reflectors of thin film solar cells

Christophe Ballif, Franz-Josef Haug, Ali Naqavi

We study light scattering and absorption in thin film solar cells, using a model system of a sinusoidally textured silver reflector and dielectric layers of ZnO and amorphous silicon. Experimental results are compared to a theoretical model based on a Rayl ...

American Institute of Physics2012

Resonances and absorption enhancement in thin film silicon solar cells with periodic interface texture

Christophe Ballif, Karin Söderström, Franz-Josef Haug, Ali Naqavi

We study absorption enhancement by light scattering at periodically textured interfaces in thin film silicon solar cells. We show that the periodicity establishes resonant coupling to propagating waveguide modes. Ideally, such modes propagate in the high i ...

American Institute of Physics2011

Understanding of photocurrent enhancement in real thin film solar cells: towards optimal onedimensional gratings

Christophe Ballif, Hans Peter Herzig, Karin Söderström, Vincent Paeder, Toralf Scharf, Ali Naqavi

Despite the progress in the engineering of structures to enhance photocurrent in thin film solar cells, there are few comprehensive studies which provide general and intuitive insight into the problem of light trapping. Also, lack of theoretical propositio ...

Optical Society of America2011

An RCWA Analysis of Solar Cell Back Reflectors: Comparison between Modelling and Experiment

Christophe Ballif, Hans Peter Herzig, Karin Söderström, Vincent Paeder, Toralf Scharf, Franz-Josef Haug, Ali Naqavi

We present a comparison between spectrally-resolved reflection measurements of gratings and theoretical predictions from RCWA approach. Diffraction intensities vary significantly with polarization, and surface plasmon absorption is observed around the onse ...

2010

Extension of Unified Formulation for the FDTD Simulation of Nonlinear Dispersive Media

Ali Naqavi, Sina Khorasani

A simple approach is extended for the simulation of Kerr-nonlinear and/or dispersive media through the finite-difference time-domain method. The scheme is able to include different types of linear and nonlinear dispersion in a single and unified formulatio ...

Institute of Electrical and Electronics Engineers2010