Xun Li, Fei Zhang

Corresponding author: Tao Xu, Kai Zhu

Communications Unit: Northern Illinois University, NREL

Perovskite solar cells, as a new photovoltaic technology with high efficiency and low cost, face many obstacles in the process of commercialization. The stability of devices has been substantially improved, but the problem of lead waste and the toxicity of lead leaking from devices has not been substantially resolved. How much lead is there? Will there be a leak? What happens after the leak? These are the problems that must be understood when perovskite cells are put into practice.

It is reported that the lead content in commercial coatings is generally 0.007g M-2, while in typical lead-based perovskite solar cells, the lead thickness is about 550 nm and the Pb concentration per unit area is about 0.75 GM -2, which is two orders of magnitude higher than the current lead paint concentration. When perovskite solar cells are used in integrated photovoltaic cells in buildings, the potential hazard of lead leakage can be considered as an environmental and public health hazard.

With this in mind, Tao Xu of Northern Illinois University and Kai Zhu of NREL et al have come up with a chemical method to ensure that more than 96% of lead leaks are isolated in case the lead-based perovskite battery components are seriously damaged.

Figure 1. Schematic diagram of device

The researchers coated the front and back of the device with an organic coating of DMDP, a lead-absorbing material that can be coated by a common solution coating method because DMDP is soluble in some polar organic solvents, such as ethanol.

DMDP coatings are highly transparent to the thickness of 0.7 to 6.89 m, and DMDP membranes are insoluble in water but have good permeability. Thus, when water infiltrates into the device, the two phosphonic acid groups in each DMDP molecule can firmly bind to Pb2+ ions (binding energy is 295.6kj mol-1), effectively absorbing Pb2+ in water.

Figure 2. Lead containment test

On the glass side of the front-facing transparent conducting electrode, a transparent lead-absorbing molecular film containing phosphonic acid groups firmly bound to lead is used to absorb the leaking lead.

On the back (metal) electrode side, a polymer film doped with a lead chelator is placed between the metal electrode and the standard PHOTOVOLTAIC packaging film. The lead-absorbing films on both sides swell when immersed in water to absorb lead rather than dissolve it, thus maintaining structural integrity and making it easy to collect lead if the device breaks down.

Figure 3. Device performance

In short, this work provides a more practical thinking and reference for the practical application of perovskite cells, and it can be felt that large-scale commercial use is not far off.

References:

Li, X., Zhang, F., He, H. et al. On-device lead sequestration for perovskite solar cells. Nature 2020.

DOI: 10.1038 / s41586-020-2001 - x.

https://doi.org/10.1038/s41586-020-2001-x