Omar A. M. Abdelraouf

Plasmonic scattering nanostructures for efficient light trapping in flat CZTS solar cells

CZTS (Cu2ZnSnS4) is a promising absorbing layer in photovoltaic devices, due to it is low cost, abundancy, and non-toxicity. However, recent developments in CZTS solar cells showed efficiency reaching barely over 9%. The low efficiency of CZTS solar cells is the main obstacle for replacing conventional high cost bulk silicon photovoltaic with CZTS solar cells. Herein, we propose an alternative route for enhancing the efficiency of CZTS solar cells by using plasmonic scattering nanostructures on the top surface of the CZTS active layer. Metamaterial and plasmonic nanostructures can confine, absorb, guide or scatter incident light in the nanoscale. Each one of these phenomena totally depends on the material type, shape, and geometrical dimensions of the used nanostructures. Therefore, theoretical study of different shapes and materials can guide the highest performance of desired phenomena. In this work, we studied the effect of changing plasmonic metal nanopyramids height, periodicity, and tapering angle on light scattering inside active layer of the CZTS solar cells. By sweeping pyramids height from 100nm to 300nm, periodicity of closed nanopyramids from 100nm to 180nm, and using pyramid base length 25nm, 50nm, 75nm, we found good enhancements in light absorption inside the active layer over reference planar CZTS structures. Each plasmonic CZTS solar cell structure is designed and analyzed using there dimensional (3D) finite element method (FEM) simulations. Using periodic boundary condition for simulating a smaller cell, and with mesh size is ten times smaller than lowest simulated wavelength. Input port energy came from air mass 1.5 sun light over wavelength range from 300nm to 800nm. Also, we studied effect of replacing molybdenum with refractory plasmonics titanium nitride (TiN). TiN is a promising plasmonic material as it has a similar plasmonic properties to gold at visible wavelength. After using TiN, we found also enhancements in light absorption. These interesting results could open a new way of integrating plasmonic scattering nanostructure inside flat CZTS solar cell for higher efficiency.

Design of optimum back contact plasmonic nanostructures for enhancing light coupling in CZTS solar cells

Thin film solar cells based on CZTS (Cu2ZnSnS4) have record efficiency in 2013 around 12.6%. Its materials are low cost, non-toxic and earth abundant and this makes it suitable low cost solar cells. Enhancing its efficiency over this limit could be achieved using nanophotonic techniques for guiding light. Our approach here is designing optimum back contact plasmonic nanostructure for increasing light trapping based on Mie theory. Using Mie theory parameters, we could identify position of electric and magnetic dipoles, absorption and scattering efficiency of different nanostructures, and select optimum nanostructure for highest back scattering light and light trapping. Our design methodology for selecting optimum back contact nanostructure includes reducing absorption efficiency, increasing scattering efficiency, and increasing back scattered light. Our simulation results indicate that, light trapping is totally depending on dimension and pitch of closed plasmonic nanostructure, a good enhancement in light trapping achieved using plasmonics structures, after using dielectric coating we found enhancement in generated photocurrent over planar back contact. In addition, our results give clearer picture about how absorption and scattering efficiency of each proposed nanostructure would change back scattered light ratio. For more accurate results, we have done all our simulations using three-dimensional models based on finite element method tool. For verifying our results, we started comparing our results of plasmonic nanostructure over substrate with previous reported work, and results matched accurately. Fabricating optimum gold nanostructure with dielectric coating over back contact of CZTS would result in increasing light trapping and its overall efficiency.

Design methodology for selecting optimum plasmonic scattering nanostructures inside CZTS solar cells

Efficiency of CZTS solar cell has made it a good candidate for low cost thin _lm solar cells, due to its low cost and earth abundant materials. Though, its efficiency barely reach 12.6% in 2013, which let great room of improvements required in its efficiency, this could be achieved using plasmonic scattering nanostructures. Designing and selecting optimum plasmonic scattering nanostructures inside active layer of CZTS solar cells would enhance light absorption and increase generated photocurrent. Using Mie theory, we could calculate absorption and scattering cross sections for any plasmonic nanostructure inside solar cells. Calculating and controlling absorption and scattering peaks would manipulate light propagation direction for highest light concentration in CZTS active layer. According to our results, we found that absorption and scattering efficiency of silver nanostructures could be controlled for enhancing light coupling over planar structure only. In addition, using dielectric coating would enhance scattering efficiency and generated more photocurrent over planar structure. All modeling done during this work made using three-dimensional finite element method simulation tool. To verify our results, we compared theoretical results of silver sphere over substrate with previous reported work, and good matching achieved. Using proposed plasmonic nanoscattering structures with certain dimension, pitch, and coating thickness would enhance overall efficiency of CZTS solar cells.

Plasmonic nanoscatter antireflective coating for efficient CZTS solar cells

Antireflective coatings have been used for reducing light reflection in many optoelectronic devices. Using these coating with thin _lm CZTS solar cell, would increase its low efficiency and make it a good alternative for bulk solar cells. Designing optimum antireflective coating requires to control light scattering directivity from subwavelength nanostructures. Mie theory could calculate absorption and scattering cross section of different nanoscatters on CZTS substrate, and it is enables us in understanding role of electric and magnetic dipoles in reducing light reflection from coated surface. Our approach is using concept of Mie theory to make design methodology for fast predicting optimum plasmonic nanoscatters dimension for lowest light reflection. Then, we swept on periodicity for examining light coupling dependency on pitch. Moreover, we made coating for plasmonic nanoscatters with dielectric materials to study possible enhancements from plasmonic and dielectric on same scatter. Our results indicate possibility of controlling absorption and scattering cross section of plasmonic nanoscatters with changing its dimensions and pitch. Also, using dielectric coating could enhance the light coupling performance over planar CZTS substrate. We suggested some nanoscatters with certain dimensions to achieve highest enhancement in light absorption inside CZTS solar cells. All calculations of this work built based on Mie theory. For verification of our results, we start by modelling of silver sphere on substrate and it gave a very good matching with previously reported work. Integrating antireflective coating with CZTS solar cells would open the door for increasing its overall efficiency beyond current limit.

Using all dielectric and plasmonic cross grating metasurface for enhancing efficiency of CZTS solar cells

CZTS (Cu2ZnSnS4) based solar cell has many advantages as its materials are earth abundant and low cost. However, its efficiency is low compared with other thin film solar cells. Enhancing efficiency of CZTS solar cell could be achieved using nanostructures for controlling light propagation using nanophotonics techniques. Recently, metamaterial has been used widely for guiding and confining electromagnetic waves over entire wave- length range. Cross grating metasurface would be possible for reducing light reflection and increasing generated photocurrent inside CZTS solar cells. Herein, we studied theoretically effect of using different plasmonic cross grating metasurface above or below CZTS active layer. Then, we replaced plasmonic material with all dielectric metasurface to compare how light losses inside metasurface would reduce and light coupled to CZTS active layer increase. Moreover, we studied how using dielectric coating for metasurface would increase or decrease active layer light absorption. Our findings indicate that, light absorption enhancement in CZTS active layer is largely depend on material, coated material, dimension and pitch of proposed cross grating wires. Our results suggest certain nanostructure to be used for getting better photocurrent and efficiency. All proposed nanostructures done in this study made in three-dimensional using finite element method simulation tool, and use measured solar spectrum as input power. Using proposed cross grating metasurface with suggested material coating, would enhance overall efficiency of CZTS solar cells.

All dielectric and plasmonic cross-grating metasurface for efficient perovskite solar cells

Recently, organic perovskite solar cell has achieved remarkable increase in its efficiency, and reached over 22% in 2017. However, its efficiency could be increased further using nanophotonic techniques for guiding incident light to perovskite active layer. Metasurface cross grating nanostructure would control light reflection and transmission over wide range of wavelength. Using metasurface with perovskite solar cell, will increase generated photocurrent and enhance overall efficiency. Our results show that light absorption enhancement and light reflection reduction are highly depending on dimensions, periodicity and coated material used of metasurface cross grating nanostructures. Controlling electric and magnetic dipoles in gold metasurface and Mie resonance dipoles in dielectric coating material would enhance generated photocurrent over planar perovskite structure. Comparison between plasmonic and all dielectric metasurface performance would give us more understanding for light reflection reduction mechanism. Using three-dimensional optical modeling based on finite element method simulation tool for all our results would enhance its accuracy. For verifying our results, we made comparison between our results and previously reported work for planar perovskite solar and good matching achieved in light absorption and generated current. Adding suggested plasmonic and dielectric metasurface cross grating nanostructures inside perovskite solar cells, will enhance its overall efficiency.

Enhancing light absorption inside CZTS solar cells using plasmonic and dielectric wire grating metasurface

Efficiency of CZTS (Cu2ZnSnS4) based thin film solar cell has witnessed rapid increase from nearly 5.7% in 2005 to more than 9% in 2016. These enhancements made CZTS solar cell a good candidate for low cost solar cells. However, low efficiency limit this choice, therefore, enhancing generated photocurrent would enhance overall efficiency. Metasurface has attracted great interest in last decade because of its ability for reducing light reflection and increasing light transmission over wide range of electromagnetic waves spectrum. Plasmonic metasurface has many advantages for antireflective surface with minor light losses disadvantages. All dielectric metasurface is promising because light losses would minimize and give better performance over plasmonic metasurface. Our results indicate that, light coupling to CZTS solar cells could be enhanced much more than planar structure after using suggested optimum dimension, pitch, coated dielectric thickness. Role of electric and magnetic diploes excited in gold wires and Mie resonance dipoles in dielectric play important role in guiding light to CZTS substrate, through our result, we suggest method for controlling them. Using three-dimensional optical modelling based on finite element method simulation tool for all our proposed structures. For verifying our results, we compared our simulated planar CZTS solar cells with fabricated one in previous work and good matching achieved for light absorption. Integrating suggested wire grating plasmonic and dielectric wire grating metasurface with planar CZTS solar cells would enhance its overall efficiency furthermore more.

Optimizing absorption and scattering cross section of metal nanostructures for enhancing light coupling inside perovskite solar cells

Metal-halide perovskite solar cells attracted more interest in last decade due to rapid enhancement in its efficiency from 3.9% in 2009 to over 20% in 2016 [1]. In this work, we studied theoretically effect of using silver nanostructures inside active layer of perovskite solar. Metal nanostructures could confine and guide electromagnetic waves at nanoscale dimensions, however these processes are highly depending on shape, dimension and type of used metal, by applying Mies theory we could compare absorption and scattering cross section of many metal nanostructures to find optimum shape and dimensions for highest light confinement in small thickness of perovskite active layer.