Theoretical analysis of the effect of conduction band offset of window/CIS layers on performance of CIS solar cells using device simulation

Minemoto, Takashi; Matsui, Takuya; Takakura, Hideyuki; Hamakawa, Yoshihiro; Negami, Takayuki; Hashimoto, Yoshihiro; Uenoyama, Takeshi; Kitagawa, Masatoshi

doi:10.1016/s0927-0248(00)00266-x

Cited by 585 publications

(466 citation statements)

References 12 publications

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“…S1a). 15 If the conduction band energy of the buffer layer is too high compared to that of the absorber layer, the positive CBO at the buffer/absorber interface creates a barrier that prevents electrons from flowing across the junction towards the transparent conducting oxide (TCO) layer ( Although it has been demonstrated that low electron carrier concentration of Zn(O,S) can improve SnS-based solar cells, this can increase contact resistance with the TCO layer by adding series resistance to the solar cell, which reduces the short-circuit current density (J SC ). While a low carrier concentration of Zn(O,S) can be beneficial for the portion of the buffer layer closer to the absorber layer to reduce possible recombination occurring at the absorber/buffer interface, a high carrier concentration of Zn(O,S) can be beneficial for the portion of the buffer layer closer to the TCO layer to reduce contact resistance.…”

Section: Introductionmentioning

confidence: 99%

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Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

Park

Jayaraman

Heasley

et al. 2014

Applied Physics Letters

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Zinc oxysulfide, Zn(O,S), films grown by atomic layer deposition (ALD) were incorporated with aluminum to adjust the carrier concentration. The electron carrier concentration increased up to one order of magnitude from 10 19 to 10 20 cm -3 with aluminum incorporation and sulfur content in the range of 0 ≤ S/(Zn+Al) ≤ 0.16. However, the carrier concentration decreased by five orders of magnitude from 10 19 to 10 14 cm -3 for S/(Zn+Al) = 0.34, and decreased even further when S/(Zn+Al) > 0.34. Such tunable electrical properties are potentially useful for graded buffer layers in thin-film photovoltaic applications. Cu 2 ZnSn(Se,S) 4 (CZTS), [3][4][5] Compared to the conventional toxic CdS buffer material for CIGS and CZTS solar cells, Zn(O,S) is composed of earth-abundant and non-toxic elements. KeywordsThis ternary n-type buffer material also has the advantage of having the ability to adjust the band alignment through fine tuning of the stoichiometry, which is easily achieved by atomic layer deposition (ALD) through varying the precursor pulse ratios. [10][11][12] Increasing the sulfur content in Zn(O,S) raises the conduction band energy, which is critical in adjusting the conduction band offset (CBO) at the buffer/absorber interface to optimize the solar cell device performance, 13 as illustrated for SnS/Zn(O,S) heterojunctions in Fig. S1 (see Ref. 14). If the conduction band energy of the buffer layer is too low compared to that of the absorber layer, the negative CBO will induce recombination at the buffer/absorber interface via defects (Fig. S1a). 15 If the conduction band energy of the buffer layer is too high compared to that of the absorber layer, the positive CBO at the buffer/absorber interface creates a barrier that prevents electrons from flowing across the junction towards the transparent conducting oxide (TCO) layer ( Although it has been demonstrated that low electron carrier concentration of Zn(O,S) can improve SnS-based solar cells, this can increase contact resistance with the TCO layer by adding series resistance to the solar cell, which reduces the short-circuit current density (J SC ). While a low carrier concentration of Zn(O,S) can be beneficial for the portion of the buffer layer closer to the absorber layer to reduce possible recombination occurring at the absorber/buffer interface, a high carrier concentration of Zn(O,S) can be beneficial for the portion of the buffer layer closer to the TCO layer to reduce contact resistance. Aluminum is a well known dopant for increasing the electron carrier concentration of ZnO for TCO applications. 18,19 In this study, we report that the electron carrier concentration of ALD Zn(O,S) can be either increased or decreased by modifying the stoichiometry of the film with aluminum incorporation, which is potentially useful for graded buffer layers in thin-film solar cell applications.A custom-built hot-wall ALD reactor was used to grow Zn(O,S) and Al-incorporated Zn(O,S) films. Films were grown at a deposition temperature of 120°C in closed valve mode...

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

Park

Jayaraman

Heasley

et al. 2014

Applied Physics Letters

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“…20 According to device simulations, a large negative CBO gives rise to an increase in the interface recombination, while a large positive CBO greater than +0.5 eV creates a barrier in the conduction band that impedes the collection of photo-generated electron. 21,22 Thus, a small positive CBO is desirable to reduce interface recombination without any loss in photo-current collection. 21,22 One of the approaches to adjust the CBO is to vary the constituent elements in the semiconductor-alloy buffer layer.…”

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confidence: 99%

“…21,22 Thus, a small positive CBO is desirable to reduce interface recombination without any loss in photo-current collection. 21,22 One of the approaches to adjust the CBO is to vary the constituent elements in the semiconductor-alloy buffer layer. For example, (Zn,Cd)S, 23 (Zn,Mg)O, 24 (Zn,Sn)O x , 25 and Zn(O,S) 26 were used in an attempt to replace CdS in CIGS solar cells.…”

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confidence: 99%

Enhancing the efficiency of SnS solar cells via band-offset engineering with a zinc oxysulfide buffer layer

Sinsermsuksakul

Hartman

Kim

et al. 2013

Applied Physics Letters

333

230

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SnS is a promising earth-abundant material for photovoltaic applications. Heterojuction solar cells were made by vapor deposition of p-type tin(II) sulfide, SnS, and n-type zinc oxysulfide, Zn(O,S), using a device structure of soda-lime glass/Mo/SnS/Zn(O,S)/ZnO/ITO. A record efficiency was achieved for SnS-based thin-film solar cells by varying the oxygen-to-sulfur ratio in Zn(O,S). Increasing the sulfur content in Zn(O,S) raises the conduction band offset between Zn(O,S) and SnS to an optimum slightly positive value. A record SnS/Zn(O,S) solar cell with a S/Zn ratio of 0.37 exhibits short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) of 19.4 mA/cm2, 0.244 V, and 42.97%, respectively, as well as an NREL-certified total-area power-conversion efficiency of 2.04% and an uncertified active-area efficiency of 2.46%.

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“…Indeed the average electrostatic potential we use demonstrates such character, validating that it provides the proper theoretical reference linking microscopic interface modelling with macroscopic screening in semiconductor interfaces. Strikingly, our calculations show that for the perfect interface the CBO = 0.83 eV, which is far from optimal, where 0-0.4 eV, 63 is thought to be best. Such a high CBO would provide a barrier preventing transport of photo-generated electrons from absorber to buffer layer.…”

Section: Resultsmentioning

confidence: 73%

Predicted roles of defects on band offsets and energetics at CIGS (Cu(In,Ga)Se2/CdS) solar cell interfaces and implications for improving performance

Xiao

Goddard

2014

The Journal of Chemical Physics

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The laboratory performance of CIGS (Cu(In,Ga)Se 2 ) based solar cells (20.8% efficiency) makes them promising candidate photovoltaic devices. However, there remains little understanding of how defects at the CIGS/CdS interface affect the band offsets and interfacial energies, and hence the performance of manufactured devices. To determine these relationships, we use density functional theory with the B3PW91 hybrid functional that we validate to provide very accurate descriptions of the band gaps and band offsets. This confirms the weak dependence of band offsets on surface orientation observed experimentally. We predict that the conduction band offset (CBO) of perfect CuInSe 2 /CdS interface is large, 0.79 eV, which would dramatically degrade performance. Moreover we show that band gap widening induced by Ga adjusts only the valence band offset, and we find that Cd impurities do not significantly affect the CBO. Thus we show that Cu vacancies at the interface play the key role in enabling the tunability of CBO. We predict that Na further improves the CBO through electrostatically elevating the valence levels to decrease the CBO, explaining the observed essential role of Na for high performance. Moreover we find that K leads to a dramatic decrease in the CBO to 0.05 eV, much better than Na. We suggest that the efficiency of CIGS devices might be improved substantially by tuning the ratio of Na to K, with the improved phase stability of Na balancing phase instability from K. All these defects reduce interfacial stability slightly, but not significantly.

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Theoretical analysis of the effect of conduction band offset of window/CIS layers on performance of CIS solar cells using device simulation

Cited by 585 publications

References 12 publications

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

Atomic layer deposition of Al-incorporated Zn(O,S) thin films with tunable electrical properties

Enhancing the efficiency of SnS solar cells via band-offset engineering with a zinc oxysulfide buffer layer

Predicted roles of defects on band offsets and energetics at CIGS (Cu(In,Ga)Se2/CdS) solar cell interfaces and implications for improving performance

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