The Effects of ZnTe:Cu Back Contact on the Performance of CdTe Nanocrystal Solar Cells with Inverted Structure

Abstract

CdTe nanocrystal (NC) solar cells have received much attention in recent years due to their low cost and environmentally friendly fabrication process. Nowadays, the back contact is still the key issue for further improving device performance. It is well known that, in the case of CdTe thin-film solar cells prepared with the close-spaced sublimation (CSS) method, Cu-doped CdTe can drastically decrease the series resistance of CdTe solar cells and result in high device performance. However, there are still few reports on solution-processed CdTe NC solar cells with Cu-doped back contact. In this work, ZnTe:Cu or Cu:Au back contact layer (buffer layer) was deposited on the CdTe NC thin film by thermal evaporation and devices with inverted structure of ITO/ZnO/CdSe/CdTe/ZnTe:Cu (or Cu)/Au were fabricated and investigated. It was found that, comparing to an Au or Cu:Au device, the incorporation of ZnTe:Cu as a back contact layer can improve the open circuit voltage (Voc) and fill factor (FF) due to an optimized band alignment, which results in enhanced power conversion efficiency (PCE). By carefully optimizing the treatment of the ZnTe:Cu film (altering the film thickness and annealing temperature), an excellent PCE of 6.38% was obtained, which showed a 21.06% improvement compared with a device without ZnTe:Cu layer (with a device structure of ITO/ZnO/CdSe/CdTe/Au).

An overview on the role of ZnTe as an efficient interface in CdTe thin film solar cells: a review

“…16(a) together with the energy band diagram using a 20 nm ZnTe:Cu back contact annealed at 200 1C, and the device yielded a PCE of 6.38%. 215 Given that a low resistive back contact is needed to fabricate high-efficiency devices, to well match the interfacial properties of ZnTe, a heavily doped p-type Cu 1.4 Te, ZnTe/Cu 1.4 Te alloyed bilayer was synthesized for application in a device with the architecture of glass/FTO/SnO 2 /CdS/CdTe/ZnTe/Cu 1.4 Te/Au, as shown in Fig. 17 with its energy band diagram.…”

“…16(a) together with the energy band diagram using a 20 nm ZnTe:Cu back contact annealed at 200 °C, and the device yielded a PCE of 6.38%. 215…”

Back contacts materials used in thin film CdTe solar cells—A review

“…Amin et al (2002) 76 tried ZnTe and Cd 0.5 Zn 0.5 Te:N back contacts to thin (1 µm CdTe) solar cells obtaining 8.3% PCE (low FF of 49%) for ZnTe/C:Cu/Ag contacted devices. Chen et al (2019) 77 studied ZnTe:Cu back contacts to CdTe using a CdSe buffer layer (ITO/ZnO/CdSe/CdTe/ZnTe:Cu/Au structure). Although an improvement over the Au only back contact was observed, the maximum PCE was 6.38%.…”

Hole Transfer Layer Engineering for CdTe Nanocrystal Photovoltaics with Improved Efficiency

“…It is well known that Cu-doped interface layer has been applied successfully to CdTe thin film solar cells prepared by close-space sublimation (CSS) method [ 11 , 12 ]. Unfortunately, fabricating a homogeneous Cu-doped layer on CdTe NC thin films remains a challenge, since Cu may diffuse quickly along the crystal boundaries of NCs and restrict further device performance improvement [ 13 ]. Yang et al [ 14 ] investigated the application of commercially available poly-[3-(potassium-6-hexanoate)thiophene-2, 5-diy] (P3KT) as a HTL for aqueous processed CdTe NC solar cells with the configuration of ITO/SnO 2 /CdS/CdTe/P3KT/MoOx/Au and found that the insertion of P3KT optimized bandgap alignment and enhanced carrier collection efficiency.…”