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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]

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]

In recent years, the power conversion efficiency (PCE) up to 20% was obtained based on CdTe solar cells consisting of Glass/SnO 2 : F/SnO 2 /CdS/CdTe/ZnTe: Cu/Au. The underlying carrier transport and collection mechanisms of this architecture become complicated while quantum efficiency with external direct current bias is tremendously informative. Quantum efficiency measurement under forward voltage changes dramatically and it is defined as apparent quantum efficiency (AQE). It is accessible to give insight to the impact of the high resistant transparent buffer layer and CdS window layer on the carrier collection mechanism and photocurrent loss. Herein, five simpler structures were fabricated and tested together with the structure mentioned above for both direct current (DC) and alternating current (AC) modes of quantum efficiency under forward bias and four types (470 nm, 525 nm, 780 nm, 850 nm) of monochromatic light to achieve a pair of I-V curves under different light intensities. Comparing the AQE acquired via applying various forward bias with different device structures along with their collection efficiency of different wavelength, it is available to establish the connection between AQE effects and device structures. The consistent tendency of the AQE response under DC mode at forward bias for different structures of CdTe devices indicates a same current direction without phase shift. While the introduction of SnO 2 buffer layer is prone to generate a large phase angle in the shortwave AQE response, resulting in AQE > 1. When there is no photoconductive CdS layer, the device photocurrent under forward bias changes slightly and uniformly in the measured spectra, avoiding intricate band diagram in the CdS region. [ABSTRACT FROM AUTHOR]