Alkali treatments of Cu(In,Ga)Se<sub>2</sub> thin‐film absorbers and their impact on transport barriers

Werner, Florian; Wolter, Max Hilaire; Siebentritt, Susanne; Sozzi, Giovanna; Napoli, Simone Di; Menozzi, Roberto; Jackson, Philip; Witte, Wolfram; Carron, Romain; Avancini, Enrico; Weiss, Thomas Paul; Buecheler, Stephan

doi:10.1002/pip.3032

Cited by 56 publications

(75 citation statements)

References 46 publications

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“…(B1) and, thus, the absolute conductance, might differ by up to 2 orders of magnitude between different devices. Furthermore, these values are likely specific to the buffer layers deposited in our lab, since, for example, in a recent study we reported a thermally activated behavior for devices fabricated at different institutes [20]. For the temperature-dependent conductance of the p-n junction also shown in Fig.…”

Section: Appendix B: Temperature-dependent Buffer Conductancementioning

confidence: 72%

“…Primarily, it has been attributed to a defect, although conflicting evidence exists concerning where these defects are located within the device [9,11,12]. This standard interpretation was recently challenged by an increasing number of publications which suggest alternative explanations for the N1 level, mostly linked to the transport characteristics of the solar-cell absorber [13,14] or to a transport barrier [7,[15][16][17][18][19][20][21] within the device.…”

Section: Introductionmentioning

confidence: 99%

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Buffer Layers, Defects, and the Capacitance Step in the Admittance Spectrum of a Thin-Film Solar Cell

Werner

Siebentritt

2018

Phys. Rev. Applied

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Defects in complex multilayered thin-film solar cells are often analyzed by capacitance-based techniques, which originally were developed for simple homojunctions in single-crystal bulk semiconductors. We discuss the impact of a capacitive and conductive buffer layer on the impedance and capacitance spectra of thin-film solar cells. While the resulting capacitance spectra are indistinguishable from those caused by a deep defect level, the buffer layer and p-n junction can clearly be distinguished in the experimental impedance spectra. Exploiting bias voltage and illumination as additional experimental parameters allows us to test a given hypothesis-deep defect or buffer layer-to explain characteristic capacitance steps in thermal admittance spectroscopy of thin-film solar cells. We address the controversial origin of the N1 signature commonly observed in admittance spectroscopy of CuðIn; GaÞSe 2 solar cells. The circuit element dominantly defining the main capacitance step in our devices is unaffected by applied bias voltage, and its conductivity increases linearly with illumination intensity. We conclude that the main capacitance step in our devices is most plausibly explained by the presence of a buffer layer connected in series to the p-n junction of the device and is not related to any deep defects or mobility freeze-out.

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Section: Appendix B: Temperature-dependent Buffer Conductancementioning

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Buffer Layers, Defects, and the Capacitance Step in the Admittance Spectrum of a Thin-Film Solar Cell

Werner

Siebentritt

2018

Phys. Rev. Applied

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“…[27] To extract the drop in capacitance and the activation energy of the capacitance step, the fitting method proposed by Weiss et al is applied to the capacitance spectra. [28] The activation energies of the main capacitance step show a good correlation to the incorporated Rb amount as depicted in Figure 7a. Consequently, a good correlation to the low-temperature activation energy from the differential resistance is obtained as represented in Figure 7b.…”

Section: Injection Barrier Formationmentioning

confidence: 75%

Injection Current Barrier Formation for RbF Postdeposition‐Treated Cu(In,Ga)Se₂‐Based Solar Cells

Weiss

Nishiwaki

Bissig

et al. 2017

Adv Materials Inter

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Among the thin‐film solar cell technologies, Cu(In,Ga)Se2‐based solar cells demonstrate the highest efficiencies, where the recent boost in efficiency is triggered by a KF postdeposition treatment (PDT). In this contribution, Cu(In,Ga)Se2‐based solar cells are fabricated using RbF PDTs after absorber layer growth with varying substrate and RbF source temperature. The electronic charge transport properties of the solar cell devices are investigated using temperature‐dependent current–voltage analysis and admittance spectroscopy. To investigate the observed transport barriers, a novel concept based on the differential series resistance is proposed. This approach is supported by simulations of current–voltage curves, which reproduce qualitatively experimental data. Experimentally, two parallel conduction paths are found, which act as barriers with different activation energies and impede the charge carrier transport. Both the thickness and height of these barriers increase with an increasing amount of incorporated Rb and can lead to losses in the fill factor and power conversion efficiency at room temperature. Etching in HCl prior to CdS buffer layer deposition reduces the barrier width and can recover these losses.

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“…The forward‐bias dark current densities were found to follow a simple diode model without signatures for interface barriers for all 3 devices. This indicates that the main admittance step is not related to a barrier but to shallow defects. Based on the activation energies of step 2, it can be observed that the activation energy of the main capacitance step decreases from 135 to 115 to 90 meV with the addition of Ga.…”

Section: Performance and Defect Analysismentioning

confidence: 95%

“…For CIS_0.95, a double step could be observed with activation energies of 40 and 135 meV. To confirm whether this capacitance step is indeed related to a defect signature or a barrier, the extracted activation energies were compared to the temperature dependences of series resistance and dark diode current from IVT measurements …”

Section: Performance and Defect Analysismentioning

confidence: 99%

High‐performance low bandgap thin film solar cells for tandem applications

Elanzeery

Babbe

Melchiorre

et al. 2018

Progress in Photovoltaics

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Thin film tandem solar cells provide a promising approach to achieve high efficiencies. | INTRODUCTIONCurrently, there is an increasing demand to provide cheap high-efficiency solar cells that can exceed state-of-the-art single-junction solar cell technologies. One approach to achieve this is through using tandem solar cells. Tandem or multijunction solar cells have the potential to achieve efficiencies of more than 30%. set the full illumination intensity for the IVT measurements. A mechanical shutter was used to allow dark and illuminated measurements within the same experiment. Admittance measurements were performed in the dark, after keeping the sample mounted in the dark at room temperature for 1 night, with an LCR meter using the same cryostat setup. All characterizations were performed after adding the ARC layer. For the extraction of the quasi-Fermi-level splitting (qFLS), photoluminescence (PL) spectra were recorded on CdS-covered absorbers in a home-built calibrated setup at room temperature under continuous monochromatic illumination with 660-nm wavelength. 27,28The spectral and absolute corrected PL spectra are converted into energy space. In a semilogarithmic plot, the high-energy wing of the PL peak is fitted linearly and is evaluated by means of the simplified Planck's generalized law, 29 providing the qFLS as well as the temperature. Figure 1A. Figure 1 A also presents the electrical behavior under light for CIS_0.95 measured in-house. Table 1 as a function of absorber bandgap are shown in Figure 2. All IV measurements were performed after adding an ARC layer.In Figure 1A, it is observed that V OC increases and J summarized in Table 1, it can be concluded that the cells lose more in recombination than in incomplete absorption (η el < η op ). Moreover, the

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Alkali treatments of Cu(In,Ga)Se₂ thin‐film absorbers and their impact on transport barriers

Cited by 56 publications

References 46 publications

Buffer Layers, Defects, and the Capacitance Step in the Admittance Spectrum of a Thin-Film Solar Cell

Buffer Layers, Defects, and the Capacitance Step in the Admittance Spectrum of a Thin-Film Solar Cell

Injection Current Barrier Formation for RbF Postdeposition‐Treated Cu(In,Ga)Se₂‐Based Solar Cells

High‐performance low bandgap thin film solar cells for tandem applications

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Alkali treatments of Cu(In,Ga)Se2 thin‐film absorbers and their impact on transport barriers

Cited by 56 publications

References 46 publications

Buffer Layers, Defects, and the Capacitance Step in the Admittance Spectrum of a Thin-Film Solar Cell

Buffer Layers, Defects, and the Capacitance Step in the Admittance Spectrum of a Thin-Film Solar Cell

Injection Current Barrier Formation for RbF Postdeposition‐Treated Cu(In,Ga)Se2‐Based Solar Cells

High‐performance low bandgap thin film solar cells for tandem applications

Contact Info

Product

Resources

About

Alkali treatments of Cu(In,Ga)Se₂ thin‐film absorbers and their impact on transport barriers

Injection Current Barrier Formation for RbF Postdeposition‐Treated Cu(In,Ga)Se₂‐Based Solar Cells