Researchers at NREL have developed a perovskite absorber composition with improved performance at higher bandgaps. Here, the optical absorber is a mixed triple-cation perovskite structure with the novel incorporation of dimethylammonium ((CH3)2NH, or “DMA”) into the fractional ‘A’ site, with an overall composition DMAxFAyCs1-x-yPbIzBr3-z, where 0 < x < 0.2, 0 < y < 1, and 0 < z < 3. The device has electrical contacts on either side of the optical absorber/emitter with at least one electrical contact allowing for partial transmission of light and that may be comprised of transparent conducting oxides, conductive polymers, small molecule organics, or metals.
The incorporation of DMA into the films allows for the formulation of higher bandgap compositions (>1.71 eV) and, in contrast to other high-bandgap formulations, removes the necessity for high fractional percentages of Bromine in the ‘X’ site. The reduction in Bromine is advantageous in that, at higher levels of Bromine incorporation (i.e. >20%) phase segregation within the film is quickly observed, leading to significant deterioration in performance. This innovation brings stability to the solar cell device while at the same time achieving high performance in the wide-bandgap range 1.7-1.9 EV, which may be useful in tandem photovoltaic device applications. The DMA-containing perovskite yields a very high photovoltaic efficiency at very low costs, and when encapsulated with an alumina layer, exhibits yet more long-term stability in air as compared to those films without DMA. Furthermore, it is highly effective in fabrication of stable tandem solar cells.
This technology is within the Perovskite Film Stability and Perovskite Chemistry groups of NREL’s perovskite portfolio. For further information regarding NREL's broader perovskite portfolio, please visit NREL's Perovskite Patent Portfolio website or contact Bill Hadley at:.