That’s not very correct the new ISS solar panels for example have a 12% efficiency they are optimized for longevity and weight.
The relatively high efficiency figures often touted for some spacecraft panels especially in low earth orbit don’t compare apples to apples as they include the additional 70-80% solar radiation that isn’t absorbed, reflected or scattered by the atmosphere.
There are some spacecraft that do use multi-junction cells with very high efficiency however those are ones which are sent far into the outer solar system like Dawn and Juno.
The relatively high efficiency figures often touted for some spacecraft panels especially in low earth orbit don’t compare apples to apples as they include the additional 70-80% solar radiation that isn’t absorbed, reflected or scattered by the atmosphere.
There are some spacecraft that do use multi-junction cells with very high efficiency however those are ones which are sent far into the outer solar system like Dawn and Juno.