In the recent years, thin film solar cell manufacturers have suffered from the abrupt decrease of silicon module price. Irrespective of the current efficiency of Cu(In, Ga) Se2 thin film solar cells being very near to the already established silicon-based photovoltaic technology, the low availability of gallium and indium in the Earth’s crust will result in their high cost, and this will definitely limit their future role in terawatt range photovoltaic applications. Therefore, researchers have shifted their attention to low cost materials based on earth abundant elements.
Fortunately, there is an attractive alternative for the preparation of indium and gallium free terawatt-scale chalcogenides. These alternatives depend on I2-II-IV-VI4 species, which include copper zin tin sulfide, copper zinc tin selenide and the related sulphur-selenium alloy. Copper manganese tin sulfide, a p-type semiconductor based fully on earth abundant as well as low cost elements, is another member of this group of materials . In view of the fact that manganese is cheaper than zinc, copper manganese tin sulfide can provide Wp cost lower as compared to copper zinc tin sulfide.
Copper manganese tin sulfide that crystalizes into a stannite structure exhibits direct band gap and high absorption coefficient all of which are necessary for photovoltaic applications. Several studies on copper manganese tin sulfide have been mainly based on single crystals and nanocrystals. However, recent studies have been reported on copper manganese tin sulfide thin films for photovoltaic applications.
Alessia Le Donne, Maurizio Acciarri and Simona Binetti at University of Milano-Bicocca in collaboration with Stefano Marchionna and Federico Cernuschi at RSE SpA grew copper manganese tin sulfide thin films through a two-step vacuum process. They grew metal precursor stacks through thermal evaporation and then heat treated them in elemental sulfur vapors. Their research work is published in Solar Energy.
The authors settled for Cu-poor/Mn-rich copper manganese tin sulfide films with Mn/Sn ratio of 1 in a bid to avoid the development of insulating and highly conductive secondary phases. The researchers tested the proposed copper manganese tin sulfide thin films by photoluminescence, Raman, Scanning Electron Microscopy and Energy Dispersive Spectroscopy.
The research team were able to obtain Cu-poor/Mn-rich copper manganese tin sulfide specimens with an acceptable homogeneity of the metal compositional ratios through a stringent control of the manganese evaporation rate. Solar cells manufactured from the films indicated good performance as opposed to a previous study. In view of the advantages of low temperature post-deposition annealing in inert and air atmosphere reported in the literature, the authors investigated the impact of thermal treatments they did between 200 and 275 °C on the copper manganese tin sulfide solar cell efficiency. The analysis encompassed both modification of material attributes and electrical performance.
The best annealing at 225 °C in air for about 40 minutes allowed for significant enhancement of their performance, open circuit voltage 354 mV, short circuit current density 5.8 mA/cm2, 40% fill factor and efficiency of 0.83%. This therefore increased the efficiency of this promising material.
A. Le Donne, S. Marchionna, M. Acciarri, F. Cernuschi, S. Binetti. Relevant efficiency enhancement of emerging Cu2MnSnS4 thin film solar cells by low temperature annealing. Solar Energy, volume 149 (2017), pages 125–131.
Go To Solar Energy