Solar energy is a promising alternative for reducing the overdependence on fossil fuels. In the last decades, solar energy has been extensively researched to improve its efficiency and applications. Among the materials used in the fabrication of solar cells, perovskite has attracted significant research attention. However, pure perovskite cannot guarantee high-performance perovskite films due to its high susceptibility to environmental factors. Therefore, it is necessary to improve the efficiency and stability of perovskite solar cells by enhancing the crystal structure through ion doping. Hybrid perovskite cells exhibit higher performance, stability, and better career charge transfer owing to their remarkable photoelectric properties, suitable band gap width, and smaller hysteresis than pure (FA/MA) PbI3 cells. Recently, multi-component mixed cation (FA/MA) Pb(I/Br) perovskite cells have demonstrated great market value in the development of photovoltaic technology.
To date, different perovskite solar cell structures have been reported. The synthesis of perovskite solar cells comprising of four component cations (RbCsFAMA) have provided more opportunities for enhancing the performance and applications of perovskite solar cells. The recent findings also revealed that various cation doping methods could be used to suppress the phase separation induced by the bromine and iodine ions enrichment, as indicated by the high stability of the devices. Additionally, the device resistance and recombination of carriers are reduced by doping three component cations with Rb +, which leads to high stability and efficiency.
Nevertheless, despite the extensive research, the mechanism of mixed ions remains underexplored with several controversies that need to be clarified. This can be attributed to the limited studies on the hysteresis and stability of mixed ions perovskite. To this end, Professor Bowen Gao and Dr. Jing Meng from Taishan University studied the effects of Rb+ and Cs+ doping on the on the crystallization process of the mixed perovskite films. In particular, RbCs(MAFA)PbI3 perovskite solar cell was proposed based on precise ions cascade regulation. The mixture of the Cs+ and Rb+ ions was embedded in the ion cascade of (MA0.5FA0.5) PbI3 to form the gradient potential. The authors aimed at improving the morphology of the perovskite film by controlling the doping ratio of the ions in the precursor solution. Their work is currently published in the journal, Applied Surface Science.
The authors observed an improvement in the morphology of the perovskite films accompanied by the transformation of the non-perovskite and PbI2 phases to the perovskite phase. This was attributed to the inhibition of the transformation of the impurity phase. The addition of the Cs+ and Rb+ ions reduced the non-radiative recombination and trap position in the RbXCsXMA(1-2X)/2FA(11-2X)/2) PbI3 film, leading to the smaller surface roughness and larger grains in the perovskite films. This improved the contact between the transport layer and the perovskite film, leading to short circuit current density and increased open-circuit voltage. At a doping concentration of 20%, the Rb0.2Cs0.2(MA0.3FA0.3)PbI3 device reported a filing factor, open-circuit voltage, short circuit current density, and filling factor of 77%, 1.25V, and 23.70 mA/cm2, respectively.
In summary, the authors reported using precise ions cascade regulation to fabricate RbCs(MAFA)PbI3 perovskite solar cells with improved efficiency. Its performance, an efficiency improvement of up to 22.81%, was superior to that of the undoped (MA0.5FA0.5) PbI3 perovskite solar cells. Moreover, this is the highest efficiency ever reported for four-component RbXCsXMA(1-2X)/2FA(11-2X)/2) PbI3 perovskite solar cells. In a statement to Advances in Engineering, the authors stated that the study advance the way for the commercialization and large-scale production of perovskite solar cells.
Gao, B., & Meng, J. (2020). RbCs(MAFA)PbI3 perovskite solar cell with 22.81% efficiency using the precise ions cascade regulation. Applied Surface Science, 530, 147240.