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Title: Light Trapping in Solar Cells: Theory and Practical Implementation

Abstract

Light trapping is a mechanism for creating enhanced absorption in a material, beyond that of a parallel polished wafer of the same material and the same thickness. Light trapping is an important feature of all solar cells, because it allows the use of thinner cells that perform equally or better than thick cells. A thinner cell leads to lower-volume recombination of photogenerated carriers, leading to higher cell performance. Thinner wafers can also help minimize the use of semiconducting material, therefore lowering the energy cost further. Light trapping in a wafer or a solar cell requires rough or textured surface(s); hence the detailed optics of light trapping is somewhat difficult to carry out. We have developed a software package, PV Optics, which performs light-trapping calculations for solar cell applications. It determines optical absorption for a given structure and calculates photocurrent available from a given solar cell structure for many cases, such as when the cell is placed directly in the sun or encapsulated in a module. The cell can have a single- or multiple-junction configuration. This paper will review the principles of light trapping and practical approaches to incorporate effective light trapping in silicon solar cells. We will demonstrate typical usemore » of PV Optics for the design of crystalline and amorphous silicon solar cells.« less

Authors:
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy Solar Energy Program
OSTI Identifier:
1120063
DOE Contract Number:
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Conference: Linking Science and Technology for Global Solutions: Technical Program of the Minerals, Metals & Materials Society (TMS) 136th Annual Meeting and Exhibition, 25 February-1 March 2007, Orlando, Florida
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; Solar Energy - Photovoltaics

Citation Formats

Sopori, B. Light Trapping in Solar Cells: Theory and Practical Implementation. United States: N. p., 2007. Web.
Sopori, B. Light Trapping in Solar Cells: Theory and Practical Implementation. United States.
Sopori, B. Mon . "Light Trapping in Solar Cells: Theory and Practical Implementation". United States. doi:.
@article{osti_1120063,
title = {Light Trapping in Solar Cells: Theory and Practical Implementation},
author = {Sopori, B.},
abstractNote = {Light trapping is a mechanism for creating enhanced absorption in a material, beyond that of a parallel polished wafer of the same material and the same thickness. Light trapping is an important feature of all solar cells, because it allows the use of thinner cells that perform equally or better than thick cells. A thinner cell leads to lower-volume recombination of photogenerated carriers, leading to higher cell performance. Thinner wafers can also help minimize the use of semiconducting material, therefore lowering the energy cost further. Light trapping in a wafer or a solar cell requires rough or textured surface(s); hence the detailed optics of light trapping is somewhat difficult to carry out. We have developed a software package, PV Optics, which performs light-trapping calculations for solar cell applications. It determines optical absorption for a given structure and calculates photocurrent available from a given solar cell structure for many cases, such as when the cell is placed directly in the sun or encapsulated in a module. The cell can have a single- or multiple-junction configuration. This paper will review the principles of light trapping and practical approaches to incorporate effective light trapping in silicon solar cells. We will demonstrate typical use of PV Optics for the design of crystalline and amorphous silicon solar cells.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • Recently, methods to enhance the optical adsorption (i.e., light trapping) of thin silicon solar cells have been investigated by several groups. We have investigated the effect of parasitic adsorption (PA) losses on light trapping in thin silicon cells. Parasitic adsorption refers to an optical adsorption process which does not generate an electron/hole pair; it competes with band-to- band adsorption to decrease the photocurrent. A simple model for light trapping that includes PA is described for interpretation of experimental data. The sub-bandgap reflectance is shown to be a sensitive and quantitative indicator of PA losses. Finally, minimization of the PA lossesmore » is shown to be as important as optimization of the light-trapping geometry for increased photogeneration in light-trapping thin silicon solar cells. 12 refs., 7 figs.« less
  • This paper describes major features of a new optical software package, PV Optics, and presents a brief summary of the results of applying this program to analyze amorphous silicon solar cells. Some examples are given, mainly to demonstrate the nature of calculations that can be performed with this program for a-Si cell design.
  • An attempt is made to assess the accuracy of the simplifying assumption of total retransmission of light inside the escape or loss cone which is made in many models of optical confinement in thin-film silicon solar cells. A closed form expression is derived for the absorption enhancement factor as a function of the refractive index in the low-absorption limit for a thin-film cell with a flat front surface and a lambertian back reflector. Numerical calculations are carried out to investigate similar systems with antireflection coatings, and the investigation of cells with a textured front surface is achieved using a modifiedmore » version of the existing ray-tracing computer simulation program TEXTURE.« less
  • The authors found that sputtered ZnO:Al films with an appropriate compact structure develop a surface texture during etching in diluted HCl with excellent optical and light trapping properties. Moreover, these texturable films have a high optical transmission and good electrical properties which are not affected by the etching process. An analysis of the film structure by HRSEM is presented. High short-circuit currents have been achieved for a-Si-H solar cells incorporating these films as TCO substrates.
  • Light trapping plays an important role to achieve high short circuit current density (Jsc) and high efficiency for amorphous/crystalline Si heterojunction solar cells. Si heterojunction uses hydrogenated amorphous Si for emitter and back contact. This structure of solar cell posses highest open circuit voltage of 0.747 V at one sun for c-Si based solar cells. It also suggests that over 25% record-high efficiency is possible with further improvement of Jsc. Light trapping has two important tasks. The first one is to reduce the surface reflectance of light to zero for the solar spectrum that Si has a response. The secondmore » one is to increase the effective absorption length to capture all the photon. For Si heterojunction solar cell, surface texturing, anti-reflectance indium tin oxides (ITO) layer at the front and back are the key area to improve the light trapping.« less