GSL, page-22

Efficiency isn't the issue, it's proving the ability to manufacture at scale with low costs, and stability/longevity. Of course efficiency is important, but perovskite is already close and rapidly improving.

https://c1cleantechnicacom-wpengine.netdna-ssl.com/files/2017/10/1-nvhVCf6nFhAYP6fM12sSng.jpeg

If efficiency was the issue, there would be no market for polycrystalline or CdTe panels, which have lower efficiency than monocrystalline cells (on a par with Pervskite as it happens), but lower cost of manufacture.

Solar cell efficiency tables (version 51)