Challenges and opportunities for an efficiency boost of next generation Cu(In,Ga)Se<sub>2</sub> solar cells: prospects for a paradigm shift

Ochoa, Mario; Buecheler, Stephan; Tiwari, Ayodhya N.; Carron, Romain

doi:10.1039/d0ee00834f

Cited by 36 publications

(38 citation statements)

References 55 publications

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“…Figure 6 shows simulation results for several L d values as a function of ΔGGI, together with the experimental Δ V OC calculated by Equation () (orange circles) of the samples listed in Table 1. Two dashed lines in Figure 6 establish the upper and lower bound for L d values that could reproduce the experimental results ( L d between 3.6 and 14.4 μm), which are in good agreement with other reports 13,14,22 . The solid lines are shown as extreme instances to exemplify the degree of V OC loss sensitivity with respect to L d .…”

Section: Resultssupporting

confidence: 88%

“…The front grading and notch are kept constant whereas the back grading was modified to obtain several GGI profiles with ΔGGI ranging from 0 to approximately 0.8 (See Figure S1). More details and material parameters used can be found elsewhere 14 …”

Section: Experimental and Simulationsmentioning

confidence: 99%

“…There is no conclusive agreement about minimum required ΔGGI. In addition, the quality of state‐of‐the‐art absorbers considerably improved following breakthroughs and developments of the past 10 years, leading to longer diffusion length 14 . It makes the control of back interface recombination become even more critical.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In,Ga)Se2 thin film solar cells

Yang

Ochoa

Hertwig

et al. 2021

Progress in Photovoltaics

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The performance of Cu(In,Ga)Se2 (CIGS) solar cells is limited by the presence of the highly recombinative CIGS/Mo interface. The recombination at the CIGS/Mo interface is influential for the open circuit voltage (VOC) in high quality CIGS absorbers with increased charge carriers diffusion length. A quantitative understanding of the role of the Ga back grading height (ΔGGI) in suppressing back interface recombination is needed. In this work, we take advantage of a low temperature process to modify the ΔGGI while keeping the composition in the notch and front regions almost unchanged. Improvement in both VOC deficit and time‐resolved photoluminescence lifetime are observed with increasing ΔGGI. With a combination of back surface modification experiments and numerical simulations, we quantify a voltage loss in ungraded devices of approximately 100 mV solely from the back interface recombination. Nice agreement between simulation and experimental data is reached while constraining the values of possible diffusion lengths. Our results suggest that a ΔGGI of about 0.50 is required to effectively suppress the back interface recombination, highlighting the importance of grading control in high‐performance CIGS solar cells and devices.

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Section: Resultssupporting

confidence: 88%

Section: Experimental and Simulationsmentioning

confidence: 99%

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Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In,Ga)Se2 thin film solar cells

Yang

Ochoa

Hertwig

et al. 2021

Progress in Photovoltaics

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“…

\overset{true¯}{P_{abs}}

and

\overset{true¯}{P_{esc}}

are obtained from previous calculations for CIGS under different scenarios. [ 45 ] For instance, considering a structure Mo/CIGS/CdS for which CIGS exhibits a band tail absorption ≈ 15 meV,

\overset{true¯}{P_{abs}}

= 62.8%, and

\overset{true¯}{P_{esc}}

= 2.1%. In this case, η int ≈ 26% for the highest quality sample characterized here.…”

Section: Resultsmentioning

confidence: 99%

Charge Carrier Lifetime Fluctuations and Performance Evaluation of Cu(In,Ga)Se₂ Absorbers via Time‐Resolved‐Photoluminescence Microscopy

Ochoa

Yang

Nishiwaki

et al. 2021

Advanced Energy Materials

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The open‐circuit voltage (VOC) is the main limitation to higher efficiencies of Cu(In,Ga)Se2 solar cells. One of the most critical parameters directly affecting VOC is the charge carrier lifetime. Therefore, it is essential to evaluate the extent to which inhomogeneities in material properties limit the carrier lifetime and how postdeposition treatments (PDTs) and growth conditions affect material properties. Time‐resolved photoluminescence (TRPL) microscopy is employed at conditions similar to one sun to study carrier lifetime fluctuations in Cu(In,Ga)Se2 with light (Na) and heavy (Rb) alkalis, different substrates, and grown at different temperatures. PDT lowers the amplitude of minority carrier lifetime fluctuations, especially for Rb‐treated samples. Upon PDT, the grains’ carrier lifetime increases, and the analysis suggests a reduction in grain boundary recombination. Furthermore, lifetime fluctuations have a small impact on device performance, whereas VOC calculated from TRPL (and continuous‐wave PL) agrees with device values within the limits of investigated PDT samples. Finally, up to about half a per cent external radiative efficiencies are experimentally determined from TRPL metrics, and internal radiative efficiencies are approximated. The findings demonstrate that the highest absorber material quality investigated is still limited by nonradiative recombination (grain or grain boundary) and is comparable to state‐of‐the‐art absorbers.

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“…[ 2 ] The steep Ga grading due to the Ga accumulation would lower down the bandgap at front surface, limiting the open‐circuit voltage ( V oc ) and fill factor (FF). [ 3 ] Solar Frontier has paid special attention to their process to control the Ga grading; [ 4 ] however, the details are not disclosed.…”

Section: Introductionmentioning

confidence: 99%

Tuning Ga Grading in Selenized Cu(In,Ga)Se₂ Solar Cells by Formation of Ordered Vacancy Compound

Cai

Lai

2020

Solar RRL

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Severe Ga accumulation at the back contact is regarded as one of the major limiting factors for high efficiency Cu(In,Ga)Se2 (CIGSe) solar cells fabricated by the sequential process. The Ga deficiency near the front surface of absorber leads to the reduction of open‐circuit voltage; however, controlling the Ga grading is quite challenging during the selenization process. Herein, the tuning of Ga profile is demonstrated by forming the ordered vacancy compound (OVC) phase at the beginning of selenization process under high Se partial pressure (PSe) with the precursor composed of a relatively high In content. The OVC phase formed with a columnar structure promotes Ga diffusion through Cu vacancies, resulting in Ga increase at the front side of CIGSe. However, high PSe also increases the thickness of MoSe2, significantly raising the series resistance. Thereby, a 5 nm TiN layer is deposited on top of Mo to suppress the formation of MoSe2. In addition, the extra Na‐contained precursor is added to increase the carrier concentration because the TiN layer also blocks the Na outdiffusion from the substrate. By controlling PSe, interlayer TiN thickness, and carrier concentration, a 16.04% record high efficiency of CIGSe solar cells (sulfur‐free) via elemental Se source is achieved.

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Challenges and opportunities for an efficiency boost of next generation Cu(In,Ga)Se₂ solar cells: prospects for a paradigm shift

Abstract: A perspective on some strategies to trigger new developments for the next generation of Cu(In,Ga)Se2 solar cells is presented.

Cited by 36 publications

References 55 publications

Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In,Ga)Se2 thin film solar cells

Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In,Ga)Se2 thin film solar cells

Charge Carrier Lifetime Fluctuations and Performance Evaluation of Cu(In,Ga)Se₂ Absorbers via Time‐Resolved‐Photoluminescence Microscopy

Tuning Ga Grading in Selenized Cu(In,Ga)Se₂ Solar Cells by Formation of Ordered Vacancy Compound

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Challenges and opportunities for an efficiency boost of next generation Cu(In,Ga)Se2 solar cells: prospects for a paradigm shift

Abstract: A perspective on some strategies to trigger new developments for the next generation of Cu(In,Ga)Se2 solar cells is presented.

Cited by 36 publications

References 55 publications

Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In,Ga)Se2 thin film solar cells

Influence of Ga back grading on voltage loss in low‐temperature co‐evaporated Cu(In,Ga)Se2 thin film solar cells

Charge Carrier Lifetime Fluctuations and Performance Evaluation of Cu(In,Ga)Se2 Absorbers via Time‐Resolved‐Photoluminescence Microscopy

Tuning Ga Grading in Selenized Cu(In,Ga)Se2 Solar Cells by Formation of Ordered Vacancy Compound

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Product

Resources

About

Challenges and opportunities for an efficiency boost of next generation Cu(In,Ga)Se₂ solar cells: prospects for a paradigm shift

Charge Carrier Lifetime Fluctuations and Performance Evaluation of Cu(In,Ga)Se₂ Absorbers via Time‐Resolved‐Photoluminescence Microscopy

Tuning Ga Grading in Selenized Cu(In,Ga)Se₂ Solar Cells by Formation of Ordered Vacancy Compound