The aim of this investigation is to apply advanced microstructural characterization techniques to study the effect of cadmium chloride treatment on the physical properties of cadmium telluride (CdTe) solar cells deposited via close-spaced sublimation and relate these to cell performance. A range of techniques have been used to observe the microstructural changes as well as the chemical changes before and after the cadmium chloride treatment. Electrical measurements that link the device performance with the microstructural properties of the cells have also been undertaken. Transmission electron microscopy (TEM) has revealed high densities of stacking faults in the as-grown CdTe samples. Further, it has been observed that these stacking faults are removed during the cadmium chloride treatment. These observations show that the presence of chlorine plays an important role in the removal of these defects and the subsequent production of high efficiency thin-film CdTe solar cells. Elemental analysis in the TEM indicates chlorine-rich regions appearing at the CdTe/CdS interface as well as at grain boundaries after the treatment.

The market for photovoltaic modules is expanding rapidly, with more than 500 GW installed capacity. Consequently, there is an urgent need to prepare for the comprehensive recycling of end-of-life solar modules. Crystalline silicon remains the primary photovoltaic technology, with CdTe and CIGS taking up much of the remaining market. Modules can be separated by crushing or cutting, or by thermal or solvent-based delamination. Separation and extraction of semiconductor materials can be achieved through manual, mechanical, wet or dry chemical means, or a combination. Crystalline silicon modules are currently recycled through crushing and mechanical separation, but procedures do exist for extraction and processing of intact wafers or wafer pieces. Use of these processes could lead to the recovery of higher grades of silicon. CdTe panels are mostly recycled using a chemical leaching process, with the metals recovered from the leachate. CIGS can be recycled through oxidative removal of selenium and thermochemical recovery of the metals, or by electrochemical or hydrometallurgical means. A remaining area of concern is recycling of the polymeric encapsulant and backsheet materials. There is a move away from the use of fluorinated backsheet polymers which may allow for improved recycling, but further research is required to identify materials which can be recycled readily whilst also being able to withstand outdoor environments for multi-decadal timespans.

This is an Open Access Article. It is published by Elsevier under the Creative Commons Attribution 4.0 Licence (CC BY). Full details of this licence are available at http://creativecommons.org/licenses/by/4.0/Cadmium telluride (CdTe) is high-efficiency commercialised thin film photovoltaic technology. However, developing a stable low-resistivity back contact to the CdTe solar cells is still an issue. High work function and low level of doping of this material don't allow to create an ohmic contact with metals directly. Copper is commonly used to lower the back contact barrier in CdTe solar cells, but an excessive amount of copper diffusing through the cell is harmful for the device performance and stability. In this work a copper-doped ZnTe (ZnTe:Cu) buffer layer was incorporated in between CdTe and gold metal contact by high-rate pulsed DC magnetron sputtering. The back contact was then activated by rapid thermal processing (RTP) resulting in spectacular improvement in key device performance indicators, open circuit voltage (VOC) and fill factor (FF)

This is an open access article under the CC BY license\ud (http://creativecommons.org/licenses/by/4.0/). The data used in this paper can be obtained from the Loughborough University data repository https://dx.doi.org/10.17028/rd.lboro.4012833.v1In photovoltaics, ZnO is widely used both as an n-type window and buffer layer and as the basis for a range of transparent conducting oxide (TCO) top contact materials. Whilst there are reports of p-type doping, there have been no successful attempts to create a p-type ZnO-based TCO. Synthesis of an effective p-type TCO could be of significant benefit, enabling further development of technologies such as bifacial and multijunction devices. This study investigates the effects of combining ZnO with CuO, an intrinsically p-type narrow band-gap metal oxide, with the aim of synthesising a range of mid to wide band-gap p-type alloys. Alloying ZnO with CuO gave a range of p-type films with varying electrical, optical and structural characteristics. XRD patterns show that as copper content was increased above 24.5% of the total metal content, crystal structure changed from a typical ZnO wurtzite structure to a CuO tenorite structure. A second change occured at 35% copper with the emergence of two further tenorite peaks. These structural changes correlate to significant local increases in band-gap, visible and infrared transmission, and resistivity. These dramatic changes correspond to relatively minor compositional variations. Through careful control of the alloy composition it is therefore theoretically possible to tailor the material properties to suit a wide range of applications, both in photovoltaics and in other fields