Caesium makes perovskite solar cells more stable
Oxford team increases thermal and photostability while maintaining high efficiency
Adding caesium to perovskite solar cells significantly increases their thermal and photostability, while maintaining high efficiency, a new study demonstrates.
Metal halide perovskite photovoltaic cells are appealing because they have the potential to boost the efficiency of commercial silicon photovoltaic cells by 20 to 30 percent, when placed on top as a second layer.
This boost occurs because perovskite cells can absorb a wider range of light, including higher-energy blue light; however, perovskite cells that reach the preferable optical band gap of ~1.75 electron volts (eV) include materials that have poor photostability and thermal stability.
David McMeekin and colleagues at the University of Oxford have reported improving the stability of these cells by partially substituting the traditional formamidinium cations with caesium cations.
Whereas conventional perovskite cells undergo unstable phases, the addition of caesium created a single crystalline phase within the cell, making it much more stable.
With an optical band gap of 1.74 eV, the caesium cell demonstrated 17 percent efficiency on its own. Layered upon silicon photovoltaics, the modified perovskite cell was able to boost the silicon cell efficiency by 7.3 percent.
This boost, in theory, means it's feasible to achieve greater than 25 percent efficiency in perovskite/Si tandem cells, the authors say.
Also since perovskites are 'tunable' to a spectrum of light, more stable perovskites hold important implications for light-emitting applications.
'A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells' by David P. McMeekin et al; Science 8 January 2016: Vol. 351 no. 6269