Preparation and characterization of pulsed laser deposited a novel CdS/CdSe composite window layer for CdTe thin film solar cell

Abstract

A novel CdS/CdSe composite window structure was designed and then the corresponding films were prepared by pulsed laser deposition as an improved window layer for CdTe-based solar cells. Two types of this composite window structure with 5 cycles and 10 cycles CdS/CdSe respectively both combined with CdS layers were prepared at 200 compared with pure CdS window layer and finally were applied into CdTe thin film solar cells. The cross section and surface morphology of the two composite window layers were monitored by using scanning electron microscopy and the result shows that the pulsed laser deposited composite window layers with good crystallinity are stacking together as the design. The devices based on CdS/CdSe composite window layers have demonstrated the enhanced photocurrent collection from both short and long wavelength regions compared to CdS/CdTe solar cell. The efficiency of the best reference CdS/CdTe solar cell was10.72%. And the device with 5 cycles CdS/CdSe composite window showed efficiency of 12.61% with V OC of 772.92 mV, J SC of 25.11 mA/cm 2 and FF of 64.95%. In addition, there are some differences which exists within the optical transmittance spectra and QE curves between the two CdS/CdSe composite window samples, indicating that the volume proportion of CdSe may influence the performance of CdTe thin film solar cell.

Structural and compositional dependence of the CdTexSe1−x alloy layer photoactivity in CdTe-based solar cells

“…In addition, Yang et al . 5 6 have shown that using CdS/CdSe window layer stacks in CdTe solar cells increases the PCE compared with traditional CdS window layers. A detailed microscopic understanding in the growth, formation and photoactivity of the CdTe x Se 1− x alloy layer formed when CdTe is deposited on CdSe is necessary to optimize the fabrication of Se-induced bandgap-graded CdTe solar cells and further increase solar property parameters, such as the open-circuit voltage ( V oc ), fill factor (FF) and the overall PCE of CdTe solar cells using Se diffusion.…”

“…The solubility of Se into CdTe is much higher than S, and, therefore, can easily diffuse from the CdSe layer into the CdTe during the CdTe growth and post-processing treatments 5 6 7 8 9 10 . The Se diffusion is expected to form a graded CdTe x Se 1− x layer that reduces the bandgap of CdTe due to bowing effects, which explains the increased photo-response for long-wavelength photons.…”

Rationally Controlled Synthesis of CdSexTe1−x Alloy Nanocrystals and Their Application in Efficient Graded Bandgap Solar Cells

“…Conversely, as Se into CdTe outstrips S in miscibility, a graded CdSe x Te 1−x layer can be formed easily when growing and post-treating the CdTe layer in the case of CdTe solar cells using CdSe as the window layer [ 22 , 23 ]. Under the “light bowing” effects, the CdSe x Te 1−x alloys exhibit a narrower bandgap than that of CdTe, elevating the external quantum efficiency (EQE) response to a longer wavelength [ 24 , 25 , 26 ]. Furthermore, CdSe is more completely consumed than other window layers, thus reducing the parasitic absorption and prolonging the short wavelength response of the device.…”

Building Solar Cells from Nanocrystal Inks

“…However, as the diffusion of Se into Te occurs more easily than S into Te, a CdSe x Te 1−x alloy layer can be easily formed when growing and post-treating the CdTe/CdSe thin film [39,40]. Due to the "light bowing" effects, CdSe x Te 1−x shows a narrower bandgap than that of CdTe, which will extend the spectrum response to a longer wavelength [41,42], and a higher J sc is expected in this case. The CdTe/CdSe solar cells prepared through magnetron sputtering techniques show a high efficiency of 15.2% coupled with a high J sc of 26.3 mA/cm 2 [43].…”