A research group led by Professor Wu Zhaoxin of Xi'an Jiaotong University (XJTU) has designed an alkali metal fluoride sandwich structure to utilize high-efficiency inverse perovskite solar energy to power indoor photovoltaic devices.

In recent years, organic-inorganic metal halide perovskite solar cells have attracted widespread attention at home and abroad, and high efficiency and high stability are the main pursuit goals.

At present, with the continuous improvement of thin film and device preparation processes, photoelectric conversion efficiency has been rapidly improved and interface problems have increasingly become a key source of limitation of device efficiency.

In particular, the energy level mismatch at the interface between the perovskite and the charge transport layer and the appearance of non-radiative recombination at the interface hinder the effective transfer of charges and also limit improvement in long-term stability of the device.

In response to the above-mentioned problems in perovskite solar devices, Wu designed an "alkali metal fluoride sandwich structure" to modify the upper and lower interfaces between the perovskite and the charge transport layer to achieve dual improvement in efficiency and stability.

Combined with DFT theoretical calculations, "alkali metal fluoride-perovskite" chelation improves the formation energy barrier of VI on the surface of perovskite, effectively inhibits interface non-radiative recombination, and significantly increases the open circuit voltage of the device.

At the same time, the alkali metal fluoride interface modification subtly regulates the surface energy level of the upper and lower interfaces of the perovskite, ensuring effective charge transfer and inhibiting the reverse recombination of electrons and holes.

In addition, through femtosecond Secondary Ion Mass Spectrometry and XPS tests, it was confirmed that an ultra-thin and dense alkali metal fluoride layer effectively achieves bidirectional ion migration inhibition as a physical barrier, which is the basic guarantee for high stability.

The adoption of the "alkali metal fluoride sandwich structure" finally achieved an efficiency of 22.02 percent of the inverted device (certified efficiency of 20.4 percent), as well as an indoor photoelectric conversion efficiency of 35.7 percent (with 1000 lux white LED light).

This work opens up a new way for the design of high-efficiency and stable perovskite solar devices for interface regulation, and provides a new strategy for the future design of high-efficiency and high-stability perovskite solar and indoor photovoltaic devices. 

The research work titled "Impermeable inorganic 'walls' sandwiching perovskite layer toward inverted and indoor photovoltaic devices" was recently published in the international journal Nano Energy.

The first authors are doctors Xu Jie and Xi Jun. In addition to Wu, Associate Professor Dong Hua, distinguished researcher Li Jingrui and Doctor Xi Jun are corresponding authors. XJTU is the first author unit and the only corresponding author unit.

Link to the paper: https://doi.org/10.1016/j.nanoen.2021.106286

Homepage of Wu: http://zhaoxinwu.gr.xjtu.edu.cn