1. Introduction

MSCE

Journal of Materials Science and Chemical Engineering

2327-6045

Scientific Research Publishing

10.4236/msce.2015.311011

MSCE-61613

Articles

Chemistry&Materials Science

Characterization of InGaN Solar Cells

Bochra

¹Bousaid

Abdelhak

LRM Laboratory, University of Abou Bekr Belka&iuml;d, Tlemcen, Algeria

13112015

0311889126 November 2015accepted 26 November 30 November 2015

2014

This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

The III-V materials are extensively studied for optoelectronic applications in the blue and UV spectral regions. InGaN ternary alloy is considered for its wide spectral coverage, good electrical characteristics and appreciable resistance to high electrical currents. For this purpose, the operation of InGaN photovoltaic cells was studied by 2D numerical simulation under AM1.5 spectrum illumination, using the software Silvaco and the two environments Athena/Atlas.

Silvaco Indium Gallium Nitride Solar Cells Numerical Simulation Atlas/Silvaco

1. Introduction

Silvaco’s simulation was based on the digital resolution of the three fundamental equations of charge transport in semiconductors; these are Poisson’s equation, continuity and transport equations for electrons and holes.

After defining the mesh of the studied structure, the materials and the chosen numerical models, the software Silvaco was used to numerically solve these equations at each node of the mesh and determine the current-vol- tage characteristic under the standard illumination conditions (AM1.5G), between 0.32 to 1.32 nm, at a temperature of 300 K.

The present study aims at finding the technological parameters that give the best output characteristics for each region of the cell. Therefore, the doping profiles and the thicknesses of these regions were varied while choosing the parameters for the best results.

2. Description of the Procedure2.1. Simulation Parameters

The material used in this work (InGaN) was defined from the parameters in the literature (Table 1).

Table 1 Simulation parameters at 300 K [<xref ref-type="bibr" rid="scirp.61613-ref1">1</xref>]

Parameters	Expressions	Values
Forbidden E_g (eV) Permittivity Electronic affinity χ (eV) State electron density N_c (10¹⁸ cm⁻³) State hole density N_v (10¹⁸ cm⁻³) Lifetime of electrons and holes Ƭ_n0 and Ƭ_p0 (ns) Surface recombination speed s_n and s_p (cm/s)	E_g = 0.74x + 3.4(1 − x) − 1.43(1 − x)x ε_r = 14.6x + 10.4(1 − x) Χ = 4.1 + 0.7(3.4 − E_g) N_c = 0.9x + 2.3(1 − x) N_v = 5.3x + 1.8(1 − x) Ƭ_n₀ = Ƭ_p₀ s_n = s_p	1.32 13.13 5.56 1.39 4.075 6.5 1000

2.2. The Cell Structure

A single-junction InGaN solar cell, with a total thickness d = 420 nm and a width of 500 microns, was selected for this study; d_E is the thickness of layer P (Emitter-acceptor), d_B is the thickness of layer N (base-donor). The electrodes are placed at the top and bottom of the structure.

2.3. Physical Models

・ Mobility

The model of Caughey-Thomas was used. The mobility depends on the carrier concentration:

With

i represents either electrons or holes;

N: doping concentration (cm⁻³);

N_g: material-dependent critical doping (cm⁻³);

g: constant (s.d.).

・ Recombination

The recombinations of Shockley-Hall were considered. They are defined by the following expression [2] :

With

n and p: concentrations of electrons and holes, respectively (cm⁻³);

n_ie: intrinsic electron concentration (cm⁻³);

Ƭ_n and Ƭ_p₀: lifetime of electrons and holes, depending on defect density (s);

E_trap: energy difference between position of energy defect and intrinsic Fermi level (eV);

k: Boltzmann constant (eV∙K⁻¹);

T_L: temperature (K).

1) Influence of doping

The cell efficiencies are calculated for different values of the doping concentration N_a of the emitter (P layer), and various values of the N_a (N_d = N_a, N_d = 3N_a and N_d = 9N_a). The results are shown in Figure 1.

The efficiency of a solar cell depends on the density of the short-circuit current I_CC, open-circuit voltage V_CO and the Fill Factor FF as follows:

It is noted that the cell efficiency slightly increases then decreases for increasing values of the doping concentration N_a. The efficiency goes through a maximum value η = 21.70% for N_a = 1 ´ 10¹⁷ cm⁻³, for the ratio N_a/N_d = 1.

2) Influence of the emitter thickness

The collection efficiency increases as the thickness of the layer P decreases, because the distance between the surface and the space charge region ZCE diminishes. The results are shown in Figure 2.

Nevertheless, the efficiency is low when the space charge region is too close to the surface. The curve shows that the best efficiency is obtained for a 60 nm-thick transmitter.

3) Influence of the diffusion length

The diffusion length is varied from 0.22 to 2.35 μm. The graph (Figure 3) shows that increasing the diffusion length allows a remarkable improvement in the cell parameters. Indeed, the efficiency increases from 16.2% to 22%.

Figure 1 Influence of emitter doping on efficiencyFigure 2 Influence of the emitter thickness on the cell efficiencyFigure 3 Influence of the diffusion length on the efficiency of the cell3. Conclusion

We tried to optimize the efficiency of the mono-junction solar cell by changing the technological parameters (doping and thickness) for each of its regions.

Cite this paper

NorBochra,BousaidAbdelhak, (2015) Characterization of InGaN Solar Cells. Journal of Materials Science and Chemical Engineering,03,88-91. doi: 10.4236/msce.2015.311011

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