Characterization of sputtered MoOx thin films with different oxygen content and their application as back contact in 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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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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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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