Phase-homogeneous mixed halide perovskites for stable tandem photovoltaics
New perovskite technology boosts solar energy efficiency.
1The Problem in Perovskite Tandem Cells
Mixed-halide wide-bandgap (WBG) perovskites, developed for use in tandem photovoltaics, face phase segregation issues even during initial film formation. This problem stems from the asymmetric nucleation of I-rich and Br-rich phases. Current homogenization strategies focus on adjusting Pb2+ coordination strength, but this method applies uniformly to all Pb2+ centers and does not solve the faster nucleation of PbBrx compared to PbIx.
2New Coordination Principle
Researchers developed a selective coordination principle: by tuning the local Lewis-base hardness at the donor atom through a molecular dipole, they constrained the polarizability of the O-donor's outermost electrons. The harder O-donor preferentially coordinates the harder Pb2+ of PbBrx, selectively slowing Br-rich nucleation and synchronizing it with PbIx. This approach enabled the formation of compositionally homogeneous WBG films.
3Improved Performance
The WBG films produced with this method were used in solar cells with bandgaps of 1.62 eV, 1.68 eV, and 1.88 eV. Each cell demonstrated enhanced power conversion efficiency (PCE) and long-term stability (1500 hours, ≥ T90, 1 sun and 65°C). These results show that the new perovskite technology can be used in practical applications.
4Tandem Cell Efficiency
Perovskite/organic tandem cells fabricated with these WBG films and an infrared-active organic cell achieved a certified efficiency of 27.0% (steady-state 26.4%). Additionally, under ISOS-L2 test conditions at 65°C, the T91 value was measured at 1000 hours. These results support the use of tandem cells in commercial applications.
5Research Team and Institutions
The study was conducted by researchers from Northwestern University, Georgia Institute of Technology, and the University of Colorado Boulder. The team combined expertise in chemistry, materials science, and electrical engineering to develop this innovative technology. The project is seen as a significant step forward in energy efficiency and sustainable energy solutions.
6Potential Impact of the Technology
This new perovskite technology could contribute to the widespread adoption of renewable energy by improving solar energy efficiency. Solving the stability and efficiency issues of tandem cells could lower the costs of photovoltaic systems, making them accessible to a broader audience. Additionally, this technology could be used in other optoelectronic applications.
7Future Research
Researchers continue to work on facilitating the industrial-scale production of this technology. They aim to optimize film formation processes to reduce production costs. Additionally, they plan to work with perovskite materials of different bandgaps to further improve efficiency.
8Conclusion and Significance
This study significantly improved the performance of tandem photovoltaics by solving the phase segregation issue in mixed-halide perovskites. The new coordination principle opens new research avenues not only for solar cells but also for other optoelectronic devices. This breakthrough holds promise for the future of clean energy technologies.