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• A facile one-step chemical method was used for the synthesis of Cu@rGO composites. • A Cu@rGO/Au system as a back contact layer was developed for the CdTe solar cells. • rGO improves the hole collection ability, and supplies an active Cu diffusion source. • Significantly enhanced performance (e.g., E ff > 16%,Voc > 830 mV; FF > 73%) was achieved for CdTe solar cells. The copper/reduced graphene oxide (Cu@rGO) composites have been synthesized via a novel and facile chemical method and been characterized by a series of measuring techniques. Then the Cu@rGO as a primary back contact has been coated on the absorber in the CdTe solar cells. After optimizing the Cu@rGO back contact processing, significantly enhanced performance especially in efficiency, open-circuit voltage and fill factor has been achieved for CdTe solar cells. The Cu@rGO supplies an effective Cu diffusion source after annealing which achieves a considerable hole concentration, and the rGO is converted into p-type conducting with Au metallization, resulting in the decrease of the back barrier and improvement of the hole collection ability. The cells with Cu@rGO/Au exhibit more outstanding photovoltaic performance than those with Cu/Au or rGO/Au back contact. [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]

Composite materials based on reduced graphene oxide decorated with cuprous telluride nanoparticles (Cu 2 Te NPs@rGO) were fabricated using a facilitated two-step method. A back-contact layer was formed using a spin-coating method for cadmium telluride (CdTe) solar cells. This research is aimed to improve the photovoltaic performance of a device containing Cu 2 Te NPs@rGO/Au back contacts. Cu 2 Te NPs, as the active copper diffusion source, dope and passivate the interfaces and grain boundaries of CdTe to form the p+-layer, which can reduce the recombination centers and back-contact barrier height. Simultaneously, the reduced graphene oxide (rGO), as a buffer and carrier transport layer, prevents excessive copper diffusion during the annealing process and improves the hole collection capacity. The p-type layer formed by the rGO contact with the Au film enhances hole transport and facilitates a low-resistance contact formation, forming a quasi-ohmic contact, and increases the open-circuit voltage and short-circuit current density. Cu 2 Te NPs@rGO/Au back contacts significantly improved the photovoltaic performance (E ff : 16.5%, V oc : 830 mV, J sc : 27.13 mA/cm2, fill factor: 73.3%, area: 0.24 cm2). The composites retain properties of Cu 2 Te NPs and rGO. Their multifunctional properties reveal the potential of Cu 2 Te NPs@rGO as the back contact and broaden the application of graphene-based composites in photovoltaic devices. Additionaly, the preparation of graphene-based composites and their application as back contact is simple and convenient. • The Cu 2 Te NPs@rGO composites is synthesized by a facilitated two-step method. • The Cu 2 Te NPs@rGO composites is firstly used as the back contact for CdTe solar cells. • Cu 2 Te NPs can effectively dope the CdTe layer, and rGO/Au can reduce the barrier height. • A quasi-ohmic contact is formed by the Cu 2 Te NPs@rGO composites. • A significant enhanced performance (e.g., Eff: 16.5%, V oc : 830 mV, J sc : 27.13 mA/cm2, FF: 73.3%, area: 0.24 cm2) is achieved for CdTe solar cells. [ABSTRACT FROM AUTHOR]

Highly efficient CdTe solar cells were fabricated by introducing rGO@CuSCN as a composite back contact. The rGO@CuSCN was prepared by convenient solution-processed method. As a Cu-doping source and electron reflection layer, CuSCN could facilitate to dope CdTe and decrease the carrier recombination on the back surface of CdTe. The rGO, as a hole transport layer, could suppress unfavorable over-diffusion of Cu and improve hole collection and transport. The results show the obvious reduction of back barrier height and decrease of the dark current density in the devices with rGO@CuSCN back contact. Using facile coating method and optimal thermal annealing for the preparation of rGO@CuSCN composite back contact, CdTe solar cell presented greatly enhanced photovoltaic performance (E ff : 16.84%, V oc : 841 mV, J sc : 26.83 mA/cm2, FF: 74.6%). • Solution-processed CuSCN and rGO composite back contact was used in CdS/CdTe solar cells. • CuSCN provides Cu-source for CdTe doping and reflects electron as a carrier selective transport layer in CdTe solar cells. • rGO improves the transfer and collection of the carriers, and inhibits the excessive diffusion of copper. • rGO@CuSCN effectively decreases the back barrier and carrier recombination in CdTe solar cells. [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]