Optoelectronic optimization of graded-bandgap thin-film AlGaAs solar cells. Part II: optimal antireflection front-surface texturing

Faiz Ahmad; Faiz Ahmad; Peter B. Monk; Akhlesh Lakhtakia

doi:10.1364/AO.500034

Applied Optics
Vol. 62,
Issue 28,
pp. 7487-7495
(2023)
•https://doi.org/10.1364/AO.500034

Optoelectronic optimization of graded-bandgap thin-film AlGaAs solar cells. Part II: optimal antireflection front-surface texturing

Faiz Ahmad, Peter B. Monk, and Akhlesh Lakhtakia

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Faiz Ahmad, Peter B. Monk, and Akhlesh Lakhtakia, "Optoelectronic optimization of graded-bandgap thin-film AlGaAs solar cells. Part II: optimal antireflection front-surface texturing," Appl. Opt. 62, 7487-7495 (2023)

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- Optical Devices, Sensors, and Detectors
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About this Article
History
- Original Manuscript: July 6, 2023
- Revised Manuscript: September 8, 2023
- Manuscript Accepted: September 10, 2023
- Published: September 26, 2023

Abstract

In Part I [Appl. Opt. 59, 1018 (2020) [CrossRef] ], we used a coupled optoelectronic model to optimize a thin-film AlGaAs solar cell with a graded-bandgap photon-absorbing layer and a periodically corrugated Ag backreflector combined with localized ohmic Pd–Ge–Au backcontacts, because both strategies help to improve the performance of AlGaAs solar cells. However, the results in Part I were affected by a normalization error, which came to light when we replaced the hybridizable discontinuous Galerkin scheme for electrical computation by the faster finite-difference scheme. Therefore, we re-optimized the solar cells containing an $n$-AlGaAs photon-absorbing layer with either a (i) homogeneous, (ii) linearly graded, or (iii) nonlinearly graded bandgap. Another way to improve the power conversion efficiency is by using a surface antireflection texturing on the wavelength scale, so we also optimized four different types of 1D periodic surface texturing: (i) rectangular, (ii) convex hemi-elliptical, (iii) triangular, and (iv) concave hemi-elliptical. Our new results show that the optimal nonlinear bandgap grading enhances the efficiency by as much as 3.31% when the $n$-AlGaAs layer is 400 nm thick and 1.14% when that layer is 2000 nm thick. A hundredfold concentration of sunlight can enhance the efficiency by a factor of 11.6%. Periodic texturing of the front surface on the scale of 0.5–2 free-space wavelengths provides a small relative enhancement in efficiency over the AlGaAs solar cells with a planar front surface; however, the enhancement is lower when the $n$-AlGaAs layer is thicker.

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	Bandgap	$E_{g, w}$	$E_{g, m i n}$	$E_{g, m a x}$						$J_{s c}$ (mA	$V_{o c}$			Rel. Enhancement
$L_{s}$ (nm)	Type	(eV)	(eV)	(eV)	A	$α$	$K$	$ψ$	$L_{x}$ (nm)	${c m}^{- 2}$ )	(mV)	FF (%)	$η$ (%)	in $η$ (%)
100	Homogeneous	1.424	1.424	–	–	–	–	–	500	19.49	1124	83.63	18.33
100	Nonlinear	1.424	1.424	1.98	0.66	8	0.66	0.65	500	19.33	1131	84.58	18.50	0.92
200	Homogeneous	1.424	1.424	–	–	–	–	–	505	22.99	1123	83.93	21.66
200	Nonlinear	1.424	1.424	1.98	0.66	8	0.66	0.65	505	22.83	1130	85.00	21.94	1.29
300	Homogeneous	1.424	1.424	–	–	–	–	–	502	25.06	1119	84.09	23.59
300	Nonlinear	2.09	1.424	1.98	0.66	8	0.66	0.65	502	23.89	1142	88.31	24.17	2.45
400	Homogeneous	2.09	1.424	–	–	–	–	–	501	25.95	1120	86.15	25.06
400	Nonlinear	2.09	1.424	1.98	1	8	0.66	0.65	501	25.64	1135	88.93	25.89	3.31
500	Homogeneous	2.09	1.424	–	–	–	–	–	500	27.13	1117	86.41	26.19
500	Nonlinear	2.09	1.424	1.98	0.99	8	0.66	0.65	500	26.76	1131	89.04	26.96	2.94
1000	Homogeneous	2.09	1.424	–	–	–	–	–	500	29.34	1104	87.08	28.26
1000	Nonlinear	2.09	1.424	1.98	0.66	8	0.66	0.65	500	29.14	1114	88.82	28.88	2.19
2000	Homogeneous	2.09	1.424	–	–	–	–	–	506	30.35	1089	87.66	28.97
2000	Nonlinear	2.09	1.424	1.98	0.3	8	0.66	0.65	506	30.14	1096	88.71	29.30	1.14

$L_{s} / B a n d g a p$	Texturing	$L_{h}$	$L_{x}$	$ζ_{h}$	$L_{{M g F}_{2}}$	$L_{Z n S}$	$J_{s c}$	$V_{o c}$	FF	$η$	Rel. Enhancement
(nm)/-	Type	(nm)	(nm)		(nm)	(nm)	(mA ${c m}^{- 2}$ )	(mV)	(%)	(%)	in $η$ (%)
200/Homogeneous	Planar	0	505	–	110	40	22.99	1123	83.93	21.66
	Rectangular	30	600	0.75	82	50	23.26	1122	83.90	21.90	1.10
	Convex hemi-elliptical	30	600	–	82	50	23.26	1122	83.90	21.90	1.10
	Triangular	50	600	–	82	50	23.23	1122	83.90	21.87	0.96
	Concave hemi-elliptical	30	600	–	82	50	23.50	1122	83.89	22.13	2.16
200/Nonlinear	Planar	0	505	–	110	40	22.83	1130	85.00	21.94
	Rectangular	30	600	0.75	70	50	23.11	1130	85.03	22.20	1.18
	Convex hemi-elliptical	30	600	–	82	50	23.11	1130	85.03	22.20	1.18
	Triangular	30	600	–	70	50	23.08	1130	85.03	22.17	0.95
	Concave hemi-elliptical	30	600	–	82	50	23.37	1130	85.01	22.45	2.32
1000/Homogeneous	Planar	0	500	–	110	40	29.34	1104	87.08	28.26
	Rectangular	30	600	0.75	70	50	29.58	1103	87.04	28.40	0.49
	Convex hemi-elliptical	35	400	–	90	50	29.58	1103	87.14	28.44	0.64
	Triangular	35	400	–	90	50	29.62	1103	8703	28.45	0.67
	Concave hemi-elliptical	30	600	–	82	50	29.49	1103	87.18	28.37	0.38
1000/Nonlinear	Planar	0	500	–	110	40	29.14	1114	88.82	28.88
	Rectangular	30	600	0.75	70	50	29.32	1113	88.93	29.02	0.48
	Convex hemi-elliptical	35	400	–	90	50	29.39	1113	88.85	29.07	0.66
	Triangular	35	400	–	90	50	29.39	1113	88.85	29.07	0.66
	Concave hemi-elliptical	30	600	–	82	50	29.27	1113	88.99	29.00	0.41
2000/Homogeneous	Planar	0	506	–	110	40	30.35	1089	87.66	28.97
	Rectangular	30	600	0.75	70	50	30.41	1088	87.61	28.98	0.03
	Convex hemi-elliptical	50	200	–	82	50	30.51	1088	87.53	29.06	0.31
	Triangular	50	200	–	82	50	30.47	1088	87.56	29.03	0.21
	Concave hemi-elliptical	25	400	–	82	50	30.45	1088	87.56	29.01	0.13
2000/Nonlinear	Planar	0	506	–	110	40	30.14	1096	88.71	29.30
	Rectangular	30	400	0.75	70	50	30.24	1094	88.68	29.34	0.14
	Convex hemi-elliptical	35	400	–	90	50	30.32	1094	88.53	29.37	0.24
	Triangular	50	150	–	82	50	30.45	1095	88.37	29.47	0.58
	Concave hemi-elliptical	25	400	–	82	50	30.29	1095	88.57	29.37	0.24

	Bandgap	$E_{g, w}$	$E_{g, m i n}$	$E_{g, m a x}$						$J_{s c}$ (mA	$V_{o c}$			Rel. Enhancement
$L_{s}$ (nm)	Type	(eV)	(eV)	(eV)	A	$α$	$K$	$ψ$	$L_{x}$ (nm)	${c m}^{- 2}$ )	(mV)	FF (%)	$η$ (%)	in $η$ (%)
100	Homogeneous	1.424	1.424	–	–	–	–	–	500	19.49	1124	83.63	18.33
100	Nonlinear	1.424	1.424	1.98	0.66	8	0.66	0.65	500	19.33	1131	84.58	18.50	0.92
200	Homogeneous	1.424	1.424	–	–	–	–	–	505	22.99	1123	83.93	21.66
200	Nonlinear	1.424	1.424	1.98	0.66	8	0.66	0.65	505	22.83	1130	85.00	21.94	1.29
300	Homogeneous	1.424	1.424	–	–	–	–	–	502	25.06	1119	84.09	23.59
300	Nonlinear	2.09	1.424	1.98	0.66	8	0.66	0.65	502	23.89	1142	88.31	24.17	2.45
400	Homogeneous	2.09	1.424	–	–	–	–	–	501	25.95	1120	86.15	25.06
400	Nonlinear	2.09	1.424	1.98	1	8	0.66	0.65	501	25.64	1135	88.93	25.89	3.31
500	Homogeneous	2.09	1.424	–	–	–	–	–	500	27.13	1117	86.41	26.19
500	Nonlinear	2.09	1.424	1.98	0.99	8	0.66	0.65	500	26.76	1131	89.04	26.96	2.94
1000	Homogeneous	2.09	1.424	–	–	–	–	–	500	29.34	1104	87.08	28.26
1000	Nonlinear	2.09	1.424	1.98	0.66	8	0.66	0.65	500	29.14	1114	88.82	28.88	2.19
2000	Homogeneous	2.09	1.424	–	–	–	–	–	506	30.35	1089	87.66	28.97
2000	Nonlinear	2.09	1.424	1.98	0.3	8	0.66	0.65	506	30.14	1096	88.71	29.30	1.14

$L_{s} / B a n d g a p$	Texturing	$L_{h}$	$L_{x}$	$ζ_{h}$	$L_{{M g F}_{2}}$	$L_{Z n S}$	$J_{s c}$	$V_{o c}$	FF	$η$	Rel. Enhancement
(nm)/-	Type	(nm)	(nm)		(nm)	(nm)	(mA ${c m}^{- 2}$ )	(mV)	(%)	(%)	in $η$ (%)
200/Homogeneous	Planar	0	505	–	110	40	22.99	1123	83.93	21.66
	Rectangular	30	600	0.75	82	50	23.26	1122	83.90	21.90	1.10
	Convex hemi-elliptical	30	600	–	82	50	23.26	1122	83.90	21.90	1.10
	Triangular	50	600	–	82	50	23.23	1122	83.90	21.87	0.96
	Concave hemi-elliptical	30	600	–	82	50	23.50	1122	83.89	22.13	2.16
200/Nonlinear	Planar	0	505	–	110	40	22.83	1130	85.00	21.94
	Rectangular	30	600	0.75	70	50	23.11	1130	85.03	22.20	1.18
	Convex hemi-elliptical	30	600	–	82	50	23.11	1130	85.03	22.20	1.18
	Triangular	30	600	–	70	50	23.08	1130	85.03	22.17	0.95
	Concave hemi-elliptical	30	600	–	82	50	23.37	1130	85.01	22.45	2.32
1000/Homogeneous	Planar	0	500	–	110	40	29.34	1104	87.08	28.26
	Rectangular	30	600	0.75	70	50	29.58	1103	87.04	28.40	0.49
	Convex hemi-elliptical	35	400	–	90	50	29.58	1103	87.14	28.44	0.64
	Triangular	35	400	–	90	50	29.62	1103	8703	28.45	0.67
	Concave hemi-elliptical	30	600	–	82	50	29.49	1103	87.18	28.37	0.38
1000/Nonlinear	Planar	0	500	–	110	40	29.14	1114	88.82	28.88
	Rectangular	30	600	0.75	70	50	29.32	1113	88.93	29.02	0.48
	Convex hemi-elliptical	35	400	–	90	50	29.39	1113	88.85	29.07	0.66
	Triangular	35	400	–	90	50	29.39	1113	88.85	29.07	0.66
	Concave hemi-elliptical	30	600	–	82	50	29.27	1113	88.99	29.00	0.41
2000/Homogeneous	Planar	0	506	–	110	40	30.35	1089	87.66	28.97
	Rectangular	30	600	0.75	70	50	30.41	1088	87.61	28.98	0.03
	Convex hemi-elliptical	50	200	–	82	50	30.51	1088	87.53	29.06	0.31
	Triangular	50	200	–	82	50	30.47	1088	87.56	29.03	0.21
	Concave hemi-elliptical	25	400	–	82	50	30.45	1088	87.56	29.01	0.13
2000/Nonlinear	Planar	0	506	–	110	40	30.14	1096	88.71	29.30
	Rectangular	30	400	0.75	70	50	30.24	1094	88.68	29.34	0.14
	Convex hemi-elliptical	35	400	–	90	50	30.32	1094	88.53	29.37	0.24
	Triangular	50	150	–	82	50	30.45	1095	88.37	29.47	0.58
	Concave hemi-elliptical	25	400	–	82	50	30.29	1095	88.57	29.37	0.24

Abstract

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Tables (2)

Equations (4)

Applied Optics