They seem to be using two different percentages which is confusing. More details can be found in "Highly efficient bifacial single-junction perovskite solar cells"[0]

Of the new panels; the front is 23% efficient and the back side is 20% efficient (see also: "an efficiency of about 91-93% of the front") so overall you collect 43%, vastly more than 26% ("current solar cell technologies") or even 30% (silicon-perovskite solar cells in lab conditions) of the available power.

[0]: https://www.sciencedirect.com/science/article/abs/pii/S25424...