Wet treatment based interface engineering for high ef®ciency Cu(In,Ga)Se 2 solar cells (original) (raw)
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The chemical effects of oxygenation of Cu(In,Ga)Se 2 (CIGS) interfaces are analyzed and are shown to involve passivation of Se de®ciencies and Cu removal. The former effect is bene®cial at grain boundaries, but detrimental at the CdS/CIGS interface. The latter effect is purely detrimental. Na and chemical bath deposition (CBD) treatments are shown to isolate thègood' oxygenation effect from thèbad' ones. Na is shown to promote oxygenation already before the deposition of the buffer and window layers, which allows a maximization of the bene®ts of Se de®ciency passivation and a minimization of Cu removal. Next, the CBD of the CdS buffer layer restores the interface charge, due to creation of Cd Cu interface donors and possibly a removal of O Se interface acceptors. This highlights the crucial role that interface redox engineering plays in optimizing the performance of CIGS-based solar cells. q 2000 Elsevier Science S.A. All rights reserved.
Thin Solid Films, 2000
The chemical effects of oxygenation of Cu(In,Ga)Se 2 (CIGS) interfaces are analyzed and are shown to involve passivation of Se de®ciencies and Cu removal. The former effect is bene®cial at grain boundaries, but detrimental at the CdS/CIGS interface. The latter effect is purely detrimental. Na and chemical bath deposition (CBD) treatments are shown to isolate the`good' oxygenation effect from thè bad' ones. Na is shown to promote oxygenation already before the deposition of the buffer and window layers, which allows a maximization of the bene®ts of Se de®ciency passivation and a minimization of Cu removal. Next, the CBD of the CdS buffer layer restores the interface charge, due to creation of Cd Cu interface donors and possibly a removal of O Se interface acceptors. This highlights the crucial role that interface redox engineering plays in optimizing the performance of CIGS-based solar cells. q 2000 Elsevier Science S.A. All rights reserved.
ACS applied materials & interfaces, 2015
We selected a sputtered-Zn(O,S) film as a buffer material and fabricated a Cu(In,Ga)Se2 (CIGS) solar cell for use in monolithic tandem solar cells. A thermally stable buffer layer was required because it should withstand heat treatment during processing of top cell. Post-annealing treatment was performed on a CIGS solar cell in vacuum at temperatures from 300 to 500 °C, to examine its thermal stability. Serious device degradation particularly in VOC was observed, which was due to the diffusion of thermally activated constituent elements. The elements In and Ga tend to out-diffuse to the top surface of the CIGS, while Zn diffuses into the interface of Zn(O,S)/CIGS. Such rearrangement of atomic fractions modifies the local energy band gap and band alignment at the interface. The notch-shape induced at the interface after post-annealing could function as an electrical trap during electron transport, which would result in the reduction of solar cell efficiency.
Wet Processing in State-of-the-Art Cu(In,Ga)(S,Se)2 Thin Film Solar Cells
Solid State Phenomena, 2018
Interface quality plays a key role in solar cell applications. Interface recombination at the front and rear surfaces, which determine this quality, have significant effects on open circuit voltage and fill factor values. In this work, several surface treatments were applied on Cu(In,Ga)Se2 (CIGS) surfaces to improve the interface quality. Besides, the passivation layer implementation was investigated to reduce interface recombination between the buffer and absorber layers.
Surface engineering in Cu(In,Ga)Se2 solar cells
Progress in Photovoltaics: Research and Applications, 2011
Surface modifications of 3-stage co-evaporated Cu(In,Ga)Se 2 (CIGS) thin films are investigated by finishing the evaporation with gallium-free (CuInSe 2 , CIS) stages of various lengths. Secondary-ion mass spectrometry shows substantial interdiffusion of indium and gallium, smearing out the Ga/(Ga+In) profile so that the addition of a CIS layer merely lowers the gallium content at the surface. For the thinnest top layer, equivalent to 20 nm of pure CIS, X-ray photoelectron spectroscopy does not detect any compositional difference compared to the reference device. The modifications are evaluated electrical both by temperaturedependent characterisation of actual solar-cell devices and by modelling, using the latest version of SCAPS-1D. The best solar-cell device from this series is obtained for the 20 nm top layer, with an efficiency of 16.6 % after antireflective coating. However, we observe a trend of decreasing open-circuit voltage for increasingly thick top layers, and we do not find direct evidence that the lowering of the gallium concentration at the CIGS surface should generally be expected to improve the device performance. A simulated device with reduced bulk and interface defect levels achieves nearly 20 % efficiency, but the trends concerning the CIS top layer remain the same.
Dependence of Cu(In,Ga)Se2 Solar Cell Performance on Cd Solution Treatment Conditions
Molecular Crystals and Liquid Crystals, 2011
In the current study, chemical bath deposition (CBD) was used to grow CdS thin films on a Cu(In,Ga)Se2 (CIGS) absorption layer, in order to examine the effects of CdS deposition conditions on the properties of CIGS solar cell devices. The dip time leading up to the start of CdS synthesis is thought to be an important process variable determining the concentration of Cd ions diffused into the CIGS as well as the condition of the CIGS surface. Accordingly, the behavior of the CIGS solar cell efficiency variation was observed while different dip times were applied, at 4, 15 and 30 minutes, respectively. When the dip time was extended, the series resistance (Rs) of the device fell by a substantial margin, leading to improved photoelectric conversion efficiency and enhanced uniformity in device properties. This can be attributed to the effect of CIGS surface cleaning by the NH 4 OH contained in the reaction solution.
Dielectric-Based Rear Surface Passivation Approaches for Cu(In,Ga)Se2 Solar Cells—A Review
Applied Sciences
This review summarizes all studies which used dielectric-based materials as a passivation layer at the rear surface of copper indium gallium (di)selenide, Cu(In,Ga)Se2, (CIGS)-based thin film solar cells, up to 2019. The results regarding the kind of dielectric materials, the deposition techniques, contacting approaches, the existence of additional treatments, and current–voltage characteristics (J–V) of passivated devices are emphasized by a detailed table. The techniques used to implement the passivation layer, the contacting approach for the realization of the current flow between rear contact and absorber layer, additional light management techniques if applicable, the solar simulator results, and further characterization techniques, i.e., external quantum efficiency (EQE) and photoluminescence (PL), are shared and discussed. Three graphs show the difference between the reference and passivated devices in terms of open-circuit voltage (Voc), short-circuit current (Jsc), and effi...
Thin Solid Films, 2007
The role of additionally textured front transparent conductive oxide − TCO (ZnO:Al) and flat TCO/metal contact on optical improvements in thin Cu(In,Ga)Se 2 (CIGS) solar cells are investigated by means of numerical simulations. A de-coupled analysis of two effects related to additional texturing of front surface of ZnO:Al TCO − (i) enhancement of light scattering and (ii) decreased total reflectance (antireflective effect) − reveals that the improvements in quantum efficiency, QE, and short-circuit current, J SC , of the solar cell originate from an antireflective effect only. In order to improve optical properties of the back contact the introduction of a TCO layer (undoped ZnO) between CIGS and back metal contact is investigated from the optical point of view. In addition to ZnO/Mo, a highly reflective ZnO/Ag contact (ZnO is also assumed to work as a protection layer for Ag) is also included in simulations. Results show significant increase in reflectance related to introduced ZnO in front of Mo. Drastically increased reflectance is obtained if ZnO/Mo is substituted with ZnO/Ag. The improvements in QE and J SC of a thin CIGS solar cell, related to ZnO/metal contacts are presented.
Fast chemical bath deposition of Zn(O,S) buffer layers for Cu(In,Ga)Se 2 solar cells
Thin Solid Films, 2011
In order to decrease the deposition time of chemical bath deposited (CBD) Zn(O,S) buffer layers in CIGSe solar cell, the alternative CBD route using H 2 O 2 as additional oxygen source has been investigated. The morphology and the optical properties of the Zn(O,S) thin films grown with and without additive have been compared through scanning electron microscopy (SEM) observations and UV-visible transmission T(λ) and reflectivity R(λ) measurements, respectively. It is observed that deposition time shorter than 5 min is sufficient to achieve films with similar properties to those deposited following the standard recipe in 15 min. The characteristics of CIGSe/Zn(O,S) structures for which the Zn(O,S) growth has been interrupted after different bath immersion durations have been investigated by XPS measurements. The evolution of the In3d and Zn2p 3/2 signals reveals that after 2 min of deposition, the Zn(O,S) layer grown by the alternative process completely covers the CIGSe and suggests that the increase of the Zn(O,S) growth rate is most probably due to the acceleration of cluster mechanism growth. A comparative study of devices buffered with the so-called fast and standard Zn(O,S) shows similar efficiencies in either case after light soaking.