Influences of buffer material and fabrication atmosphere on the electrical properties of CdTe solar cells

Abstract

The electrical properties such as interface energy barriers, defect energy levels, and densities dictate the performance of thin film solar cells. Here, we show that these properties can be quantified in cadmium telluride (CdTe) thin‐film solar cells using admittance spectroscopy‐based techniques. Our results reveal that the electrical properties in CdTe thin‐film solar cells depend on both buffer material and the fabrication atmosphere. We find that only a negligible front contact barrier exists at the CdS/CdTe front junction regardless of the fabrication atmospheres, while an obvious front barriers are observed at the ZnMgO (ZMO)/CdTe junctions. Both CdS/CdTe and ZMO/CdTe solar cells exhibit back contact barrier. The energy level of defects is shallower in CdS/CdTe cells than in ZMO/CdTe cells. The fabrication atmosphere influences the electrical properties, i.e., an oxygen‐free atmosphere reduces the front and back barrier heights and lowers the energy level of defects. The results provide critical insights for understanding and optimizing the performance of CdTe thin‐film solar cells.

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

“…In the literature, various approaches for wet treatment have been documented, namely dipping the substrate in the solution or dropping the solution on the substrate surface and annealing step can be performed at different temperatures for different periods and in various atmospheres (air, vacuum, pure O2, etc.). After the residual removal stage and before the back contact formation, devices can be smoothly etched in a bromine/methanol solution to remove the oxidization if full cell fabrication is targeted [12,13]. In general, CdCl 2 improves the short circuit current and open circuit voltage through enhancing the crystallite grain nucleation in CdTe, recrystallization, surface amendment, grain boundaries passivation, doping concentration modification, assisting inter-diffusion at the interface, defect density amending, and boosting lifetime of charge carriers in CdTe layer [14].…”

CuSCN as the Back Contact for Efficient ZMO/CdTe Solar Cells

“…Another reason is the reduced carrier recombination at the back interface between CdTe and the metal electrode, which can be confirmed by the absence of severe roll-over and cross-over effects in the J-V curves at high forward bias for the CdTe-CuSCN devices. The roll-over effect is commonly an indicator of insufficient copper doping on the rear side of CdTe film [34][35][36], and the cross-over effect is due to photoconductivity in the buffer layer which could be caused by the aggregation of copper in the buffer layer. [37] For this sake, the CdTe-Cu device delivers an efficiency of 9.49%, with V OC of 0.786 V, J SC of 24.8 mA/cm 2 , and FF of 48.7%.…”

Optical Properties of Magnesium-Zinc Oxide for Thin Film Photovoltaics

“…Over these last several years, it has been reported that resistive oxide materials can improve the open circuit voltage of the CdTe solar cell by reducing interfacial recombination at the semiconductor n - p junction [ 9 , 10 , 11 ]. In fact, it has been demonstrated that a high-quality junction can be achieved between a high resistivity transparent (HRT) layer and a p -type CdTe absorber layer even without the thin CdS or CdS:O layer, depending on the precise band alignment [ 12 ] and the front barrier height [ 13 ] at the HRT/(absorber layer) interface.…”

“…It was observed that when a MZO thin film is applied in a heterojunction with a p -type semiconductor, the conduction band minimum of the MZO shifts closer to the vacuum level with increasing Mg content x [ 19 , 21 ]. This shift can increase V OC in a heterojunction solar cell by reducing the conduction band offset [ 13 , 19 , 22 , 23 ]. In general, however, MZO thin films may exhibit poor stability due to the possible presence of multiple phases including metastable crystal structures [ 22 ].…”