The research team found that sodium, contrary to common belief, does not decrease per se indium and gallium interdiffusion, while instead hindering intergrain diffusion by segregating at grain boundaries.
A research group from the University of Luxembourg has conducted a study that is said to change 20-year old assumptions on the chemical processes of solar cell manufacturing.
According to the scientists, the addition of sodium to the light absorbing layer of the cell, which according to common belief is responsible for inhibiting the mixing of gallium and indium, may be realized through a different approach, and a “more demanding fabrication strategy.”
Under the current traditional concept of cell manufacturing, the addition of sodium is made after the growth process of the light absorbing layer is concluded.
The Luxembourg researchers, instead, believe that if the absorber is made of only one grain, the addition of sodium can be made during the growth process. This, according to them, has the advantage of helping to homogenize the distribution of the elements.
“Instead, it is suggested that sodium promotes indium and gallium intragrain diffusion, while it hinders intergrain diffusion by segregating at grain boundaries,” the research team stated. “The deeper understanding of dopant-mediated atomic diffusion mechanisms should lead to more effective chemical and electrical passivation strategies, and more efficient solar cells,” it went on to say.
The authors of the report have concluded that the addition of sodium has the dual effect of homogenising the elements inside each grain and of slowing down homogenisation in the interplay between grains. “This gives us the opportunity to rethink how we produce solar cells. In the future, these insights might lead to improvements in the manufacturing process,” said the research coordinator, Philip Dale.