Multi-Material Front Contact for 19% Thin Film Solar Cells

Here we present a comprehensive investigation of TiO 2 -Cu 2 O hetero-junction solar cells with different back contacts (Au, ITO, Cu or Ag). Combinatorial hetero-junction libraries consisting of a linear TiO 2 thickness gradient produced by spray pyrolysis and a bell shaped Cu 2 O profile synthesized by pulsed laser deposition were chosen to investigate the impact of the two metal oxide layer thicknesses. The back contacts were deposited as round patches onto a grid of 13 Â 13 points, 169 contacts for each contact material, forming a library containing 4 Â 13 Â 13 = 676 back contacts. Each back contact represented a solar cell with an individual TiO 2 and Cu 2 O thickness. I-V measurements show that all four materials provide an ohmic contact and that the open circuit voltage of B300 mV is rather independent of both layer thicknesses and contact material. The size of the Cu 2 O crystals drastically decreases with distance from the center of deposition, which leads to a drastic increase of series resistance when the crystal size is o50 nm.

Applied Sciences, 2022

In the competition of solar cell efficiency, besides top-performance multijunction cells, tandem cells based on perovskites are also breaking efficiency records to enter into the 30% range. Their design takes advantage of the rapid development of perovskite cells, and the good sharing of the available spectrum between the perovskite, absorbing at short wavelengths, and the c-Si or similar lower band gap material, working at longer wavelengths. In this paper, we present a novel tandem solar cell that combines crystalline silicon (c-Si) and perovskites cells. We analyzed the device with computational electromagnetism based on the finite element method. Our design arranges the perovskite solar cell as a multilayer 1D grating, which is terminated with a gold thin film (top metallic contact). This multilayer nanostructure is placed on top of the c-Si cell and a thin protective dielectric layer of aluminum nitride covers the whole device. The short-circuit current of the perovskite cell i...

Solar Energy Materials and Solar Cells, 2016

Resistive oxide materials play an important role in the front contact of CdTe solar cells. The highresistance transparent (HRT) or "buffer" layer has been used extensively in CdTe thin-film photovoltaics to enable a reduction in CdS thickness while maintaining near-maximum device voltage and fill factor. SnO 2and ZnO-based alloys were tested as HRT layers on a fluorine-doped tin oxide transparent conducting oxide. SnO 2-based alloy HRT layers were deposited via atmospheric pressure chemical vapor deposition (APCVD). Alloying ZnO with MgO to create Mg x Zn 1−x O (MZO) via radio-frequency sputter deposition was explored as a way to reduce the electron affinity of ZnO HRT layers. To fully understand the behavior of these materials, many devices were fabricated with either no CdS layer, a sublimated CdS layer, or a sputtered, oxygenated CdS layer. MZO layers resulted in high open-circuit voltage and device efficiency even with the complete elimination of the CdS layer. In both HRT systems, controlling electron affinity to optimize front contact band alignment is an important consideration. Band measurements using photoelectron spectroscopy and synchrotron techniques correlate band alignment measurements with efficiency parameters in the design of HRT and CdS layers.

Energies

It is well known that PV thin films can be deposited by an extensive range of more or less expensive and complicated techniques (such as sputtering, chemical vapor deposition (CVD), physical vapor deposition (PVD), pulsed laser deposition, atomic layer deposition (ALD)). The present paper focuses on TCO layers applied by chosen techniques, including mainly the ALD and CVD methods. Thin layers of transparent conductive oxides constitute a well-known group of materials with unique properties. Oxides such as ZnO, SnO2, and In2O3 are the most significant materials of this type; some of them are discussed in the paper. From the application point of view in the photovoltaic industry, the goal is to apply a method that will provide the highest value of electric charge conductivity while maintaining the minimum value of absorption in the layer and a reduced value of the reflection coefficient. The implementation of significant achievements in the coming decade is for developing guidelines f...

2019

Many different solar cell technologies have been developed over the last years, all aiming to improve efficiency in energy conversion, while reducing material expense and cost of production, which is difficult task to fulfil. In order to gain this goal, the SiTaSol project explores to increase the efficiency of inexpensive c-Si solar cells up to 30% by integrating III-V semiconductors as top absorbers. The aim of this thesis is to investigate the metallization of front contact solar cells by low cost deposition methods like inkjet and spin-coating. The copper nanoparticles ink was printed on different substrate such as glass, GaAs and Si. Afterwards were examined the sintering of printed copper nanoparticles ink by using a laser as a high speeds sintering technique. The resistivity of sintered structures was measured and plotted to determine the sheet resistance and contact resistance in the GaAs and Si substrate. Therefore, this work presents experimental investigation of the sinte...

Solar Energy Materials and Solar Cells, 2010

Cadmium telluride (CdTe) thin film solar cell has long been recognized as a leading photovoltaic candidate for its high efficiency and low cost. A numerical simulation has been performed using AMPS-1D simulator to explore the possibility of higher efficiency and stable CdS/CdTe cell among several cell structures with indium tin oxide (ITO) and cadmium stannate (Cd 2 SnO 4) as front contact material, tin oxide (SnO 2), zinc oxide (ZnO) and zinc stannate (Zn 2 SnO 4) as buffer layer, and silver (Ag) or antimony telluride (Sb 2 Te 3) with molybdenum (Mo) or zinc telluride (ZnTe) with aluminium (Al) as back contact material. The cell structure ITO/i-ZnO/CdS/CdS x Te 1 À x /CdTe/Ag has shown the best conversion efficiency of 16.9% (Voc ¼0.9 V, Jsc ¼ 26.35 mA/cm 2 , FF¼0.783). This analysis has shown that ITO as front contact material, ZnO as buffer layer and ZnTe or Sb 2 Te 3 back surface reflector (BSR) are suitable material system for high efficiency (4 15%) and stable CdS/CdTe cells. The cell normalized efficiency linearly decreased at a temperature gradient of À 0.25%/1C for ZnTe based cells, and at À 0.40%/1C for other cells.

Organic halide perovskites have been gained importance as a new class of propitious semiconductor material for photovoltaics with excellent light harvesting properties and remarkably high power conversion efficiency. Due to different working mechanisms, the model for perovskite solar cells differs from that of silicon solar cells and Dye Sensitized Solar Cells. A thorough understanding of the role of each component in solar cells and their effects as a whole is still required for further improvement in photovoltaic conversion efficiency. This paper focuses the effect of different transparent conducting oxides (TCO) like FTO, ATO and ITO as front contact on performance of TiO2-based perovskite solar cell. Efficient collection of the charge carriers depends upon the work function of front contact. With the program wx-AMPS, the planar heterojunction-based perovskite solar cells are simulated in this work. From the simulation result, it is found that TCO with lower work function is desirable. Strikingly, efficiency over 27% is obtained from perovskite solar cell with FTO contact under the moderate simulation conditions.

2021

CdTe thin film (TF) solar cells are most promising in commercial stage photovoltaic (PV) technologies. Cell contacts and interface defects related opto-electrical losses are still vital to limit its further technological benefit. Thin film PV cells voltage and fill factor loss lessening purpose carrier selective back contact selection with band matching interface layers are essential. Beside that buffer and active layer thickness selection is vital for field assisted selective carrier collection. The suitable emitter or buffer layer thickness and band gap matching to the active layer is potential to lessen parasitic absorption and shallow recombination loss. In this purpose SCAPS software based ZnO and SnO2 TCO as well as CdS and CdSe buffer impact are numerically analyzed. The TCO, emitter, back surface field layer and metal contacts effects on electrical performance is studied. In the model, TCO and back contact barrier thickness is shown significant to progress electrical perform...

IEEE Journal of Photovoltaics

In this study, Cu(In, Ga)Se 2 solar cells with a high bandgap (1.31 eV) and a flat Ga profile ([Ga]/([Ga]+[In]) 0.60) were examined. For absorber layer thicknesses varying from 0.60 to 1.45 µm, the Mo rear contact of one set of samples was passivated with an ultrathin (27 nm) Al 2 O 3 layer with point contact openings, and compared with reference samples where the rear contact remained unpassivated. For the passivated samples, mainly large gains in the short-circuit current led to an up to 21% (relative) higher power conversion efficiency compared with unpassivated cells. The differences in temperature-dependent current voltage behavior between the passivated and the unpassivated samples and the thin and the thick samples can be explained by an oppositely poled secondary photodiode at the rear contact.

Advanced Materials Interfaces, 2017

Thin film solar cells based in Cu(In,Ga)Se2 (CIGS) are among the most efficient polycrystalline solar cells, surpassing CdTe and even polycrystalline silicon solar cells. For further developments, the CIGS technology has to start incorporating different solar cell architectures and strategies that allow for very low interface recombination. In this work, we study and characterize 350 nm CIGS solar cells with a rear interface passivation strategy. The rear passivation was achieved using an Al2O3 nanopatterned point structure. Using the cell results, photoluminescence measurements and detailed optical simulations based on the experimental results, we show that by including the nanopatterned point contact structure, the interface defect concentration lowers, which ultimately leads to an increase of solar cell electrical performance mostly by increase of the open circuit voltage. Gains to the short circuit current are distributed between an increased rear optical reflection and also due to electrical effects. Our approach of mixing several techniques allowed us to make a discussion considering the different passivation gains which has not been done in detail previous works. A solar cell with a nanopatterned rear contact and a 350 nm thick CIGS absorber provided an average power conversion efficiency close to 10%.

Optical Materials Express, 2019

This paper presents a novel design for the top contact of thin film photovoltaic (PV) solar cells. The new top contact is formed by fabricating a 20nm thin honeycomb shaped silver mesh on top of an ultra-thin 13nm of indium tin oxide. The new top contact offers the potential to reduce the series resistance of the cell while increasing the light current via plasmonic resonance. Using the nano-bead lithography technique the honeycomb top contact was fabricated and electrically characterized. The experimental results verified the new contact reduces the sheet resistance by about 40%. Numerical simulations were then used to analyze the potential performance enhancement in the cell. The results suggest the proposed top contact integrated with a typical thin film hydrogenated amorphous silicon PV device would lead to more than an 8% improvement in the overall efficiency of the cell.

Beilstein journal of nanotechnology, 2018

Molybdenum (Mo) is the most commonly used material as back contact in thin-film solar cells. Adhesion of Mo film to soda-lime glass (SLG) substrate is crucial to the performance of solar cells. In this study, an optimized bilayer structure made of a thin layer of Mo on an ultra-thin chromium (Cr) adhesion layer is used as the back contact for a copper zinc tin sulfide (CZTS) thin-film solar cell on a SLG substrate. DC magnetron sputtering is used for deposition of Mo and Cr films. The conductivity of Mo/Cr bilayer films, their microstructure and surface morphology are studied at different deposition powers and working pressures. Good adhesion to the SLG substrate has been achieved by means of an ultra-thin Cr layer under the Mo layer. By optimizing the deposition conditions we achieved low surface roughness, high optical reflectance and low sheet resistivity while we could decrease the back contact thickness to 600 nm. That is two thirds to half of the thickness that is currently be...

Progress in Photovoltaics: Research and Applications, 2020

We fabricate and characterize methylammonium lead halide perovskite film as a novel back contact to CdTe thin film solar cells. We apply 0.75 µm perovskite film at the interface of CdCl 2 activated and Cu doped CdTe surface and complete the device with Au back contact. We use Cu/Au back contact as a reference to compare results with novel back contact. Our investigation shows that incorporation of thin layer of perovskite film, before the back contact metal reduces back contact barrier effect and improves FF and V OC of the solar cells. Our low temperature JV resultsprove that thin film perovskite is very necessary component in CdTe solar cells to reduce back contact barrier, to minimize interface or surface recombination, to improve collection efficiencies, and to increase the efficiency of solar cells. Our best device shows 7% increase in V OC to 0.875 V and 7% increase in FF with the highest FF of 81% and solar cell's efficiency finally increases by 10% with the use of MAPb(I 1-x Br x) 3 as an interface layer. 1 | INTRODUCTION With a bandgap of 1.45 eV and high absorption coefficient (>10 4 cm-1) near the band edge, CdTe is an excellent material for photovoltaic technology. 1 However, the laboratory scale best CdTe solar cell's efficiency is still 25% less than that of its detailed-balance limit. 2-3 The back contact on CdTe thin film solar cells has great importance for both scientific and industrial interests as it influences the efficiency and long term stability of the solar cells. The development of an efficient back contact on p-CdTe is a difficult task because of high electron affinity and band gap of CdTe. As the work function of commonly available metals is smaller than the work function of CdTe, Schottky junction is formed at the CdTe/back contact metal interface. 4 The diode formed at the CdTe/metal interface has direction opposite to the p-n junction diode formed at CdS/CdTe hetero-interface and lowers the overall built-in potential and open circuit voltage (V OC) of the solar cells.The CdTe solar cell's efficiency is mostly affected by excessive nonradiative recombination loss due to the high contact resistance and the difficulty in increasing the This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Solar Energy Materials and Solar Cells, 2005

Device performance of thin film CdTe/CdS solar cells having different methods for fabricating the primary back contact are presented. Wet and dry methods for forming the primary contact (Cu 2 Te) were evaluated with Cu layers from 0 to 15 nm. Extensive analysis of J-V curves is presented, including effects of temperature, intensity and accelerated stress. A procedure for recontacting stress-degraded cells allowed separation of contact and junction degradation modes. The junction recombination is shown to be a Shockley-Read-Hall mechanism. Stress increases the recombination current density J 0 by 2-3 orders of magnitude, resulting in a loss in V oc of 100-200 mV which is not restored with recontacting. Rollover is eliminated by recontacting the device while fill factor is partially restored with recontacting. For devices with a Cu layer, no significant differences in illuminated solar cell performance between the wet and dry process were observed before or after stress, but there were large differences in the dark J-V related to a blocking contact. To first order, unstressed devices without Cu contact layers behave similar to stressed devices with Cu; lower V oc , higher resistance, and appearance of a blocking contact. r

IEEE Journal of Photovoltaics, 2017

The choice of back contact plays a key role in the fabrication of a CdTe thin film solar cell. Material with low electric resistivity, relatively high work function, and thermal stability is needed to form a low barrier contact on a CdTe absorber film. In this work, thin CuO layer was employed as a buffer layer between p-type CdTe and metal electrode. Quantitative band alignment measurement demonstrated that a relatively low energy barrier (∼0.44 eV) was formed at the CuO/CdTe interface. CdTe solar cell stability was significantly enhanced when a CuO buffer layer and less Cu were employed in the back contact.