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[Display omitted] • CH 3 NH 3 Pb(I 1-x Br x) 3 perovskite thin films are successfully applied as copper-free back contact layers for CdTe solar cells. • The facile deposition process of back contact layers. • The uniformity of CdTe solar cell is improved after applying CH 3 NH 3 Pb(I 1-x Br x) 3 back contact layers. • CdTe solar cell with a CH 3 NH 3 Pb(I 1-x Br x) 3 back contact layer exhibits good stability. In this study, bromide-iodide lead perovskite (CH 3 NH 3 Pb(I 1−x Br x) 3) thin films were fabricated and applied as copper-free back contact layers for CdTe solar cells. The results reveal that the open-circuit voltage (V oc) and fill factor (FF) of the CdTe solar cells are greatly enhanced by the utilization of perovskite back contact layers. This is mainly due to the evidently reduced charge transportation barrier at the back contact, which is verified by temperature-dependent current–voltage (J-V-T) and apparent quantum efficiency (AQE) measurements. Specifically, after the application of perovskite back contact layer, the best-performing device shows 15.80% improvement in efficiency (from 10.82 to 12.53%), with V oc and FF increasing by 3.94% and 6.91%, respectively. Besides, the overall uniformity of the solar cells is also improved by the perovskite back contact, suggested by laser beam induced current (LBIC) results. Further simulation results confirm the experimental results and clarify the optimized cell performance by perovskite back contact layer in terms of both energy band alignment and charge carriers' recombination. In addition, in the simulation section, we have also investigated the effect of the bandgap, thickness and doping level of perovskite and the doping level of CdTe on the cell performances. The experiments and the numerical simulation reported in this work suggest perovskite a potential copper-free back contact layer for the fabrication of efficient CdTe solar cells. [ABSTRACT FROM AUTHOR]

Developing a good back contact material is important for high efficiency CdTe solar cells. In this work, the graphite oxide (GO) was prepared by the Hummers method through liquid oxidization, and the Bi-doping reduced graphene oxides (Bi@RGO) with different concentrations were synthesized by a chemical reduction of GO and BiCl 3 aqueous solution using hydrazine hydrate. The doping concentration of bismuth was varied by controlling the mass ratio of GO/BiCl 3 . The peaks of bismuth and RGO can be easily observed in the X-ray diffraction patterns. Both Raman spectra analysis and infrared spectra analysis also show that RGO is reduced successfully. Transmission electron microscopy shows Bi nanoparticles are entrapped inside the flake-like RGO. Furthermore, Bi-containing RGO/Au system was used as a back contact to CdTe thin film solar cells. The devices with Bi-containing RGO layers were fabricated and their photovoltaic characteristics such as short circuit current density, open circuit voltage, fill factor and efficiency were obtained. The results illustrate that Bi@RGO improves the hole collection ability, and supplies an active Bi diffusion source for the absorption layer, thereby enhancing CdTe solar cell performance. [ABSTRACT FROM AUTHOR]

The short-wavelength response for traditional CdS/CdTe thin film solar cells was dramatically restricted by the CdS window layer. In order to increase short-wavelength light collection, we tried to replace CdS with Mg x Zn 1−x O (MZO). The short-wavelength quantum efficiency ( QE ) response was obviously increased to more than 80% at 400 nm, while fill factor (FF) and open circuit voltage ( V oc ) for CdTe solar cells were decreased. This decrease was mainly caused by the weak build-in potential formed by the MZO/CdTe heterojunction, which resulted in insufficient driving force to repel the photo-generated carriers. Hence, the thin CdS buffer layer was introduced between MZO and CdTe to improve the built-in potential. It efficiently increased the build-in potential from 0.369 to 0.579 V with an obvious improvement of FF and V oc . But this interlayer caused QE losses to some degree in the short-wavelength region. To avoid these losses, a composite CdS/CdSe buffer layer was incorporated in the CdTe solar cells. CdSe acted as a protective layer to avoid the excessive CdS consumption during the high temperature deposition processing of the CdTe absorption layer. Meanwhile the formation of CdSe x Te 1−x by inter-diffusion extended the long-wavelength response. Thus, cell performance was enhanced with a relatively high build-in potential 0.517 V and a substantial improvement of the QE response. [ABSTRACT FROM AUTHOR]

Copper doping in polycrystalline CdTe thin films and optimal band alignment at the CdTe/back-contact interface are critical for obtaining high performance devices. A CuCl 2 solution treatment was used in this work to enhance the p-doping of CdTe. The carrier density of CdTe was increased from 4.72 × 10 13 to 1.11 × 10 14 cm −3 and the open circuit voltage of the device was obviously improved more than ~50 mV from 728 to 783 mV. In order to further improve device performance, Te/Cu bilayer using rapid thermal processing was implemented to reduce barrier at the back contact. The short time-high temperature process efficiently activated the Te/Cu bilayer back contact and precisely controlled the Cu diffusion. The proper dose of Cu diffusion can further increase the p-doping of CdTe (~2.22 × 10 14 cm −3 ), resulting in the apparent increase in response from the CdS spectral region. The chemical reaction occurred between Te and Cu after rapid thermal processing treatments causing the formation of the Cu x Te phases, which can form a barrier in the conduction band to reflect electrons and reduce recombination at the back contact. With the increase of the temperature, the open circuit voltage of the device increased. However, the device with excessive Cu contacted at higher temperature showed the reduction in response in the long-wavelength region and decrease in fill factor due to the formation of much more Cu-related recombination states. Finally, open circuit voltage of > 820 mV, and fill factor of > 72% for CdTe solar cells with an area of 0.24 cm 2 were achieved. [ABSTRACT FROM AUTHOR]

Phase control is important to obtain high-performance CdTe solar cells when copper telluride is used as a back-contact for CdTe solar cells. In this paper single-phase CuTe was mainly controlled by the Cu/Te ratio via a co-evaporation method in combination with rapid thermal processing treatments. The alloy thin films as-deposited were mainly amorphous. After thermal treatments, the films experienced the phase transformation from mixed phases of CuTe and Cu 1.4 Te to single phase CuTe and then to coexisting phases. Single phase CuTe thin films were p-type semiconductor compounds and had a high carrier concentration, ∼10 21 cm −3 . With the copper telluride buffer layer, device performance than those without the buffer layer has been obtained. Moreover, single-phase orthorhombic CuTe contact buffer layer obviously improved diode characteristics and enhanced the device performance. [ABSTRACT FROM AUTHOR]

Ohmic back contact is one of the keys to fabricate high efficient CdTe solar cells, as it can improve fill factor FF and open-circuit voltage V oc. In this work, antimony-containing reduced graphene oxide (RGO) was prepared and used as a back contact for CdTe thin film solar cells, in which antimony is an effective dopant for CdTe and RGO acts as a hole transport layer and diffusion barrier of antimony in the solar cells. Post deposition annealing was performed to activate the back contact layer and passivate the interface defect states. Electrical performance and apparent quantum efficiency characterization were performed to investigate device performance of CdTe solar cells with antimony-containing RGO back contacts. The results indicate that, the introduction of extrinsic doping near the CdTe back surface serves to reduce the back contact depletion width and enhance the built-in potential to enable the tunnelling of majority carrier holes through the barrier, and the RGO is beneficial for the formation of Ohmic back contact on CdTe. [ABSTRACT FROM AUTHOR]