Deposition temperature induced conduction band changes in zinc tin oxide buffer layers for Cu(In,Ga)Se2 solar cells

Lindahl, Johan; Keller, Jan; Donzel‐Gargand, Olivier; Szaniawski, Piotr; Edoff, Marika; Törndahl, Tobias

doi:10.1016/j.solmat.2015.09.048

Cited by 66 publications

(60 citation statements)

References 39 publications

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“…Higher band gap energies are attained at lower T ALD , likely due to an inhibited crystal growth of ZnO in an amorphous matrix. The size of the small crystallites results in band gap widening by quantum confinement effects . The cation ratio was kept constant ([Sn] / ([Zn] + [Sn]) ≈ 0.17) in all buffer layers.…”

Section: Resultsmentioning

confidence: 99%

“…Figure shows how the conduction band alignments are expected to change when T ALD and GGI are varied for CdS and for ZTO with varying band gap. The figure is constructed from values found in the literature …”

Section: Resultsmentioning

confidence: 99%

“…The formation of nanosized ZnO crystallites results in a controlled band gap widening by quantum confinement effects. The crystallite size is reduced with reduced growth temperature leading to an increase in band gap and conduction band energy level …”

Section: Introductionmentioning

confidence: 99%

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Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Larsson

Nilsson

Keller

et al. 2017

Progress in Photovoltaics

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Tandem solar cell structures require a high-performance wide band gap absorber as top cell. A possible candidate is CuGaSe 2 , with a fundamental band gap of 1.7 eV. However, a significant open-circuit voltage deficit is often reported for wide band gap chalcopyrite solar cells like CuGaSe 2 . In this paper, we show that the open-circuit voltage can be drastically improved in wide band gap p-Cu(In,Ga)Se 2 and p-CuGaSe 2 devices by improving the conduction band alignment to the n-type buffer layer. This is accomplished by using Zn 1−x Sn x O y , grown by atomic layer deposition, as a buffer layer. In this case, the conduction band level can be adapted to an almost perfect fit to the wide band gap Cu(In,Ga) It has been proven difficult to maintain a good device quality when the gallium content is increased. The main problem is that the opencircuit voltage (V oc ) does generally not scale with the band gap energy as predicted, and it tends to saturate for absorber band gap energies above roughly 1.3 eV. 7,8 This lack of performance in high gallium CIGS devices has been the subject of numerous studies. 7-11The dominating recombination paths, in CuGaSe 2 devices, have been assigned to tunneling enhanced recombination either in the space-charge region or at the interface. 12,13 A possible explanation is trap states formed by cation anti-site (In Cu /Ga Cu ) or anion vacancy (V Se ) defects that become deeper positioned within the band gap when the gallium content increases, and thereby form more effective recombination centers. 11 Furthermore, the difference between the Fermi level and the valence band energy at the absorber surface seems to remain constant around 0.8 eV, independently of gallium content. 13 Consequently, the Fermi level position at the absorber/buffer interface is closer to the middle of the band gap at high gallium contents, and no beneficial type inversion can be expected. Thus, the influence of recombination close to or at the interface appears to become more prominent when the CIGS band gap is widened. The bulk recombination rate is also expected to increase with a large number of these defects, but it has not In the first section of this study, the growth and material characterization of nongraded CIGS absorbers with varying gallium contents (0.3 ≤ GGI ≤ 1) deposited in a single-stage co-evaporation process are described. These absorbers are applied in the second section, where we use the temperature dependence of ALD grown ZTO buffer layers to show that the V oc deficit in wide band gap CIGS can be reduced by improving the absorber/buffer conduction band alignment.In the last section, we further investigate the effect of an improved band alignment by using CuGaSe 2 absorbers of higher material quality, evaporated in a 3-stage type process. 21-24It can be observed in the SEM images that the grain size is reduced with increased GGI. This general observation is often reported in the literature. The grain size reduction has been found to be influenced by a number of factors, such as film t...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Larsson

Nilsson

Keller

et al. 2017

Progress in Photovoltaics

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“…The base parameters for the CIGS cell structure with CdS buffer used for the simulation are shown in Table 1 [1,3,4,11,16,17]. The most important parameters of different buffer layer materials needed for the simulations are depicted in Table 2 [4,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”

Section: Methodsmentioning

confidence: 99%

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se₂Photovoltaic Cell Applications with Optimized Absorber Thickness

Asaduzzaman

Hosen

Ali

et al. 2017

International Journal of Photoenergy

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Absorber layer thickness gradient in Cu(In 1−x Ga x )Se 2 (CIGS) based solar cells and several substitutes for typical cadmium sulfide (CdS) buffer layers, such as ZnS, ZnO, ZnS(O,OH), Zn 1−x Sn x O y (ZTO), ZnSe, and In 2 S 3 , have been analyzed by a device emulation program and tool (ADEPT 2.1) to determine optimum efficiency. As a reference type, the CIGS cell with CdS buffer provides a theoretical efficiency of 23.23% when the optimum absorber layer thickness was determined as 1.6 μm. It is also observed that this highly efficient CIGS cell would have an absorber layer thickness between 1 μm and 2 μm whereas the optimum buffer layer thickness would be within the range of 0.04-0.06 μm. Among all the cells with various buffer layers, the best energy conversion efficiency of 24.62% has been achieved for the ZnO buffer layer based cell. The simulation results with ZnS and ZnO based buffer layer materials instead of using CdS indicate that the cell performance would be better than that of the CdS buffer layer based cell. Although the cells with ZnS(O,OH), ZTO, ZnSe, and In 2 S 3 buffer layers provide slightly lower efficiencies than that of the CdS buffer based cell, the use of these materials would not be deleterious for the environment because of their non-carcinogenic and non-toxic nature.

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“…The buffer layer role is to ensure good electrical and optical interface properties between the CIGS absorber and the ZnO layers, and therefore the buffer layer plays a decisive role in the solar cell performance as mentioned by Lindahl et al [12] The I(V) curve with ZnO buffer layer is shown in figure 3. According to the various curves I (V), it is noted the same shape.…”

Section: Buffer Layer Zno (Zno:f) Doping Influencementioning

confidence: 99%

Numerical Simulation of CuInSe<sub>2</sub> (CIS) Thin Film Solar Cell with (ZnO, ZnO:F) Buffer Layers

Belal¹

2017

AJN

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This study focuses on the solar cells based on CIS simulation with buffer layer zinc oxide (ZnO) and fluorinedoped zinc oxide (ZnO:F). ZnO is a multifunctional material with several applications in electronics and photovoltaics, with multiple possibilities of synthesis involve inexpensive methods. ZnO (ZnO:F) is a prominent candidate to be an alternative buffer layer to so-called toxic cadmium sulphide (CdS) in CIS based solar cells. A promising result has been achieved with an efficiency of 22% with Voc = 0.565 V, Jsc = 45 mA/cm 2 and fill factor = 82% by using ZnO (ZnO:F) as a buffer layer. It is also found that the high efficiency of CIS absorber layer thickness is between 1500nm and 2000nm. Our results are in good agreement with those reported in the literature from experiments.

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Deposition temperature induced conduction band changes in zinc tin oxide buffer layers for Cu(In,Ga)Se2 solar cells

Cited by 66 publications

References 39 publications

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se₂Photovoltaic Cell Applications with Optimized Absorber Thickness

Numerical Simulation of CuInSe<sub>2</sub> (CIS) Thin Film Solar Cell with (ZnO, ZnO:F) Buffer Layers

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Deposition temperature induced conduction band changes in zinc tin oxide buffer layers for Cu(In,Ga)Se2 solar cells

Cited by 66 publications

References 39 publications

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Record 1.0 V open‐circuit voltage in wide band gap chalcopyrite solar cells

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se2Photovoltaic Cell Applications with Optimized Absorber Thickness

Numerical Simulation of CuInSe&lt;sub&gt;2&lt;/sub&gt; (CIS) Thin Film Solar Cell with (ZnO, ZnO:F) Buffer Layers

Contact Info

Product

Resources

About

Non-Toxic Buffer Layers in Flexible Cu(In,Ga)Se₂Photovoltaic Cell Applications with Optimized Absorber Thickness

Numerical Simulation of CuInSe<sub>2</sub> (CIS) Thin Film Solar Cell with (ZnO, ZnO:F) Buffer Layers