Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells

As-doped polycrystalline ZnTe layers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated as a back contact for CdTe solar cells. While undoped ZnTe films were essentially insulating, the doped layers showed significant rise in conductivity with increasing As concentration. High p-type carrier densities up 4.5 × 1018 cm−3 was measured by the Hall-effect in heavily doped ZnTe:As films, displaying electrical properties comparable to epitaxial ZnTe single crystalline thin films in the literature. Device incorporation with as-deposited ZnTe:As yielded lower photovoltaic (PV) performance compared to reference devices, due to losses in the open-circuit potential (VOC) and fill factor (FF) related to reducing p-type doping density (NA) in the absorber layer. Some minor recovery observed in absorber doping following a Cl-free post–ZnTe:As deposition anneal in hydrogen at 420 °C contributed to a slight improvement in VOC and NA, highlighting the significance of back contact activation. A mild CdCl2 activation process on the ZnTe:As back contact layer via a sacrificial CdS cap layer has been assessed to suppress Zn losses, which occur in the case of standard CdCl2 anneal treatments (CHT) via formation of volatile ZnCl2. The CdS sacrificial cap was effective in minimising the Zn loss. Compared to untreated and non-capped, mild CHT processed ZnTe:As back contacted devices, mild CHT with a CdS barrier showed the highest recovery in absorber doping and an ~10 mV gain in VOC, with the best cell efficiency approaching the baseline devices.

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17.8%-efficient Amorphous Silicon Heterojunction Solar Cells on p-type Silicon Wafers

MRS Proceedings ◽

10.1557/proc-0910-a26-05 ◽

2006 ◽

Vol 910 ◽

Cited By ~ 2

Author(s):

Qi Wang ◽

Matt P. Page ◽

Eugene Iwancizko ◽

Yueqin Xu ◽

Yanfa Yan ◽

...

Keyword(s):

Solar Cells ◽

Solar Cell ◽

Amorphous Silicon ◽

High Efficiency ◽

Short Circuit ◽

Open Circuit ◽

Layer Growth ◽

Surface Recombination Velocity ◽

Back Contact ◽

P Type

AbstractWe have achieved an independently-confirmed 17.8% conversion efficiency in a 1-cm2, p-type, float-zone silicon (FZ-Si) based heterojunction solar cell. Both the front emitter and back contact are hydrogenated amorphous silicon (a-Si:H) deposited by hot-wire chemical vapor deposition (HWCVD). This is the highest reported efficiency for a HWCVD silicon heterojunction (SHJ) solar cell. Two main improvements lead to our most recent increases in efficiency: 1) the use of textured Si wafers, and 2) the application of a-Si:H heterojunctions on both sides of the cell. Despite the use of textured c-Si to increase the short-circuit current, we were able to maintain the same 0.65 V open-circuit voltage as on flat c-Si. This is achieved by coating a-Si:H conformally on the c-Si surfaces, including covering the tips of the anisotropically-etched pyramids. A brief atomic H treatment before emitter deposition is not necessary on the textured wafers, though it was helpful in the flat wafers. It is essential to high efficiency SHJ solar cells that the emitter grows abruptly as amorphous silicon, instead of as microcrystalline or epitaxial Si. The contact on each side of the cell comprises a thin (< 5 nm) low substrate temperature (~100°C) intrinsic a-Si:H layer, followed by a doped layer. Our intrinsic layers are deposited at 0.3-1.2 nm/s. The doped emitter and back-contact layers were deposited at a higher temperature (>200°C) and grown from PH3/SiH4/H2 and B2H6/SiH4/H2 doping gas mixtures, respectively. This combination of low (intrinsic) and high (doped layer) growth temperatures was optimized by lifetime and surface recombination velocity measurements. Our rapid efficiency advance suggests that HWCVD may have advantages over plasma-enhanced (PE) CVD in fabrication of high-efficiency heterojunction c-Si cells; there is no need for process optimization to avoid plasma damage to the delicate, high-quality, Si wafers.

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Morphology of CdS thin films: Pinholes and their effect on open circuit voltage in CdS/CdTe solar cells

2011 37th IEEE Photovoltaic Specialists Conference ◽

10.1109/pvsc.2011.6186282 ◽

2011 ◽

Cited By ~ 5

Author(s):

M. A. Tashkandi ◽

W. S. Sampath

Keyword(s):

Thin Films ◽

Solar Cells ◽

Open Circuit Voltage ◽

Open Circuit ◽

Cdte Solar Cells ◽

Cds Thin Films

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Electrical properties of N-type CdS and P-type CdTe thin films in CdS/CdTe solar cells

Proceedings of the 20th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) ◽

10.1109/ipfa.2013.6599187 ◽

2013 ◽

Author(s):

Jingjin Wu ◽

Ferryanto Ang ◽

Cezhou Zhao ◽

Jeremy S Smith

Keyword(s):

Thin Films ◽

Solar Cells ◽

Electrical Properties ◽

Cdte Solar Cells ◽

Cdte Thin Films ◽

P Type

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Preparation of Cu2Te Thin Films and Back-Contact Formation of CdTe Solar Cells

Japanese Journal of Applied Physics ◽

10.1143/jjap.48.085501 ◽

2009 ◽

Vol 48 (8) ◽

pp. 085501 ◽

Cited By ~ 14

Author(s):

Bin Lv ◽

Xia Di ◽

Wei Li ◽

Lianghuan Feng ◽

Zhi Lei ◽

...

Keyword(s):

Thin Films ◽

Solar Cells ◽

Back Contact ◽

Contact Formation ◽

Cdte Solar Cells

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Chalcogenide glass-ceramic with self-organized heterojunctions: application to photovoltaic solar cells

EPJ Photovoltaics ◽

10.1051/epjpv/2018002 ◽

2018 ◽

Vol 9 ◽

pp. 3 ◽

Cited By ~ 2

Author(s):

Xianghua Zhang ◽

Ilia Korolkov ◽

Bo Fan ◽

Michel Cathelinaud ◽

Hongli Ma ◽

...

Keyword(s):

Thin Films ◽

Solar Cells ◽

Chalcogenide Glass ◽

Glass Ceramic ◽

Short Circuit ◽

Short Circuit Current ◽

Open Circuit ◽

Iodine Doping ◽

P Type ◽

Photovoltaic Solar Cells

In this work, we present for the first time the concept of chalcogenide glass-ceramic for photovoltaic applications with the GeSe2–Sb2Se3–CuI system. It has been demonstrated that thin films, deposited with the sputtering technique, are amorphous and can be crystallized with appropriate heat treatment. The thin film glass-ceramic behaves as a p-type semiconductor, even if it contains p-type Cu2GeSe3and n-type Sb2Se3. The conductivity of Sb2Se3has been greatly improved by appropriate iodine doping. The first photovoltaic solar cells based on the association of iodine-doped Sb2Se3and the glass-ceramic thin films give a short-circuit current density JSCof 10 mA/cm2and an open-circuit voltage VOCof 255 mV, with a power conversion efficiency of about 0.9%.

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Highly Arsenic Doped CdTe Layers for the Back Contacts of CdTe Solar Cells

MRS Proceedings ◽

10.1557/proc-1012-y12-08 ◽

2007 ◽

Vol 1012 ◽

Cited By ~ 18

Author(s):

Vincent Barrioz ◽

Yuri Y. Proskuryakov ◽

Eurig W. Jones ◽

Jon D. Major ◽

Stuart J.C. Irvine ◽

...

Keyword(s):

Solar Cells ◽

Series Resistance ◽

Chemical Vapour ◽

Cdte Layer ◽

Open Circuit ◽

Organic Chemical ◽

Back Contact ◽

Cdte Solar Cells ◽

Current Voltage ◽

Metal Organic

AbstractIn an effort to overcome the lack of a suitable metal as an ohmic back contact for CdTe solar cells, a study was carried out on the potential for using a highly arsenic (As) doped CdTe layer with metallization. The deposition of full CdTe/CdS devices, including the highly doped CdTe:As and the CdCl2 treatment, were carried out by metal organic chemical vapour deposition (MOCVD), in an all-in-one process with no etching being necessary. They were characterized and compared to control devices prepared using conventional bromine-methanol back contact etching. SIMS and C-V profiling results indicated that arsenic concentrations of up to 1.5 × 1019 at·cm-3 were incorporated in the CdTe. Current-voltage (J-V) characteristics showed strong improvements, particularly in the open-circuit voltage (Voc) and series resistance (Rs): With a 250 nm thick doped layer, the series resistance was reduced from 9.8 Ω·cm2 to 1.6 Ω·cm2 for a contact area of 0.25 cm2; the J-V curves displayed no rollover, while the Voc increased by up to 70 mV (~ 12 % rise). Preliminary XRD data show that there may be an As2Te3 layer at the CdTe surface which could be contributing to the low barrier height of this contact.

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Solution-processed Nanocrystal Based Thin Films as Hole Transport Materials in Cadmium Telluride Photovoltaics

MRS Advances ◽

10.1557/adv.2018.349 ◽

2018 ◽

Vol 3 (41) ◽

pp. 2441-2447 ◽

Cited By ~ 6

Author(s):

Ebin Bastola ◽

Kamala Khanal Subedi ◽

Khagendra P. Bhandari ◽

Randy J. Ellingson

Keyword(s):

Thin Films ◽

Solar Cells ◽

Cadmium Telluride ◽

Valence Band ◽

Hole Transport ◽

Transport Layer ◽

Back Contact ◽

Iron Pyrite ◽

Solution Processed ◽

Cdte Solar Cells

ABSTRACTThe cadmium telluride (CdTe) photovoltaic (PV) comprise an efficient and cost-effective technology for harvesting solar energy. However, device efficiency remains limited in part by low-open circuit voltage (VOC) and fill factor (FF) due to inefficient transport of photo-generated charge carriers. Given the deep valence band of CdTe, the use of copper/gold (Cu/Au) as a back contact serves primarily to narrow the width of the inherent Schottky junction evident in CdTe solar cells (in our laboratory, Cu/Au has been used as a standard back contact). For efficient transport of carriers to and into the back contact, a hole transport layer (HTL) is desired with valence band edge comparable to that of CdTe (∼ -5.9 eV). Here, we report solution-processed nanocrystal (NCs) based thin films as HTLs in CdTe solar cells. The earth abundant materials we discuss include iron pyrite (FeS2), nickel-alloyed iron pyrite (NixFe1-xS2), zinc copper sulfide (ZnxCu1-xS) nanocomposites, and perovskite-based films. The FeS2 and NixFe1-xS2 NCs are synthesized by a hot-injection route, and thin films are fabricated by drop-casting, and spin-coating techniques using colloidal NCs. ZnxCu1-xS thin films are fabricated by chemical bath deposition. These NC-based thin films are applied and studied as the HTLs in CdTe devices. On using these materials, the device performance can be increased up to 10% compared to the standard Cu/Au back contact. Here, we discuss the benefits, challenges, and opportunities for these back contact materials in CdTe photovoltaics.

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First-principles Study of Back Contact Effects on CdTe Thin Film Solar Cells

MRS Proceedings ◽

10.1557/proc-1268-ee02-04 ◽

2010 ◽

Vol 1268 ◽

Author(s):

Mao-Hua Du

Keyword(s):

Thin Film ◽

Solar Cells ◽

First Principles ◽

Cell Performance ◽

Thin Film Solar Cells ◽

Back Contact ◽

Cdte Thin Film ◽

Solar Cell Performance ◽

Cdte Solar Cells ◽

P Type

AbstractForming a chemically stable low-resistance back contact for CdTe thin film solar cells is critically important to the cell performance. This paper reports theoretical study of the effects of the back contact material, Sb2Te3, on the performance of the CdTe solar cells. First-principles calculations show that Sb impurities in p-type CdTe are donors and can diffuse with low diffusion barrier. There properties are clearly detrimental to the solar cell performance. The Sb segregation into the grain boundaries may be required to explain the good efficiencies for the CdTe solar cells with Sb2Te3 back contacts.

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Importance of electron current in p-type CdTe in CdS/CdTe thin film solar cells at forward bias

MRS Proceedings ◽

10.1557/proc-668-h9.5 ◽

2001 ◽

Vol 668 ◽

Cited By ~ 7

Author(s):

Jutta Beier ◽

Marc Köntges ◽

Peter Nollet ◽

Stefaan Degrave ◽

Marc Burgelman

Keyword(s):

Thin Film ◽

Solar Cells ◽

Minority Carrier ◽

Voltage Dependence ◽

Forward Bias ◽

Back Contact ◽

Cdte Solar Cells ◽

Dependent Behavior ◽

Measurement Results ◽

P Type

ABSTRACTIn previous work [1,2], we modeled the cross-over of the I-V curves of thin film CdS/CdTe solar cells in terms of an electron (minority carrier) current in the vicinity of the back contact. In this work, we focus on the necessary extension of this analytical model based on a series of measurement results. Especially the wavelength and voltage dependence of the current at forward bias is illustrated in these measurements. The various possible causes for this kind of behavior are discussed and modeled. The extensions to the previous model, needed to describe the voltage and wavelength dependent behavior of I-V curves of real CdTe/CdS solar cells, are proposed.

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