High efficiency CdTe solar cells by low temperature deposition with MgZnO HRT layer

CdTe solar cells have shown high efficiency and the technology is scalable. As a result thin film CdTe modules are competitive with crystalline silicon modules. Thin film CdTe devices with efficiency above 22% have been reported using high substrate temperatures during the deposition process. It is known that high substrate temperatures result in large grain size with a reduced number of grain boundaries and this is believed to contribute to the high efficiency. However, use of high temperature requires robust substrates and excludes the use of most flexible substrate materials. It also involves higher energy consumption and more complicated machinery. In this work we present a process for high efficiency solar cells with an improved front contact, by introducing magnesium-doped zinc oxide high resistance transparent layer. By optimizing the fabrication process we have achieved a conversion efficiency exceeding 16%, which is one of the highest reported for substrate temperatures below 500°C

Magnesium-doped zinc oxide as a high resistance transparent layer for thin film CdS/CdTe solar cells

Magnesium-doped Zinc Oxide (MZO) was used as an alternative high resistance transparent layer for CdS/CdTe thin film solar cells. Thin films of MZO were deposited by RF magnetron sputtering and deposited on an Indium Tin Oxide contact (ITO). Thin film CdTe devices including a MZO high resistance transparent layer deposited at above 300◦C yielded a mean efficiency exceeding 10.5 %. This compares with an efficiency of 8.2 % without the MZO layer. The improvement in efficiency was due to a higher open circuit voltage and fill factor. Lowering the deposition temperature of MZO reduced the performance of the devices

CdTe-based thin film photovoltaics: recent advances, current challenges and future prospects

Cadmium telluride (CdTe)-based cells have emerged as the leading commercialized thin film photovoltaic technology and has intrinsically better temperature coefficients, energy yield, and degradation rates than Si technologies. More than 30 GW peak (GWp) of CdTe-based modules are installed worldwide, multiple companies are in production, modules are shipping at up to 18.6% efficiency, and lab cell efficiency is above 22%. We review developments in the science and technology that have occurred over approximately the past decade. These achievements were enabled by manufacturing innovations and scaling module production, as well as maximizing photocurrent through window layer optimization and alloyed CdSexTe1-x (CST) absorbers. Improved chlorine passivation processes, film microstructure, and serendipitous Se defect passivation significantly increased minority carrier lifetime. Efficiencies >22% have been realized for both Cu and As doped CST-based cells. The path to further efficiency gains hinges primarily on increasing open circuit voltage (Voc) and fill factor (FF) through innovations in materials, fabrication methods, and device stacks. Replacing the longstanding Cu doping with As doping is resulting in better module stability and is being translated to large-scale production. To realize 25% efficiency and >1 V Voc, research and development is needed to increase the minority carrier lifetime beyond 100 ns, reduce grain boundary and interface recombination, and tailor band diagrams at the front and back interfaces. Many of these goals have been realized separately however combining them together using scalable manufacturing approaches has been elusive to date. We review these achievements and outstanding opportunities for this remarkable photovoltaic technology.</p