A simple search of the 'net will answer the question far better than this attack on Shellenberger. It will show that rare earth minerals can be used in PV panels as doping elements. Interestingly enough it is especially Perovskite PV cells which seem to benefit from the use of these additives [1,2]:
(1) Recently, use of rare earth (RE) ions doped nanomaterials in PSCs, has been identified as an effective means to address the aforementioned issues by expanding the range of absorption spectra minimizing the non-absorption loss of solar photons, enhancing light scattering and improving operational stability.
(2) Rare earth ion doped nanomaterials can be used in perovskite solar cell to expand the range of absorption spectra and improve the stability due to its up conversion and down conversion effect. This article reviews recently progress in using rare earth ion doped nanomaterials in mesoporous electrodes, perovskite active layers, and as an external function layer of perovskite solar cell.
That's just in the lab. If you buy PV modules right now the cells will not be doped with rare earth elements. And almost everything demonstrated in the lab doesn't progress beyond there (which is fine; that's how technology R&D works.)
I think the closest one could come to making the "REE in solar" claim make sense would be decoloring agents for the glass. Cerium could be used for this, but I think manganese is cheaper.
(1) Recently, use of rare earth (RE) ions doped nanomaterials in PSCs, has been identified as an effective means to address the aforementioned issues by expanding the range of absorption spectra minimizing the non-absorption loss of solar photons, enhancing light scattering and improving operational stability.
(2) Rare earth ion doped nanomaterials can be used in perovskite solar cell to expand the range of absorption spectra and improve the stability due to its up conversion and down conversion effect. This article reviews recently progress in using rare earth ion doped nanomaterials in mesoporous electrodes, perovskite active layers, and as an external function layer of perovskite solar cell.
[1] https://www.sciencedirect.com/science/article/abs/pii/S10020...
[2] https://www.sciencedirect.com/science/article/abs/pii/S13877...