[kazinator]

Efficiency isn't everything. If you want to transfer solar energy directly to a mobile motor, such as one which moves a car, the solar cells to do that have to be mounted on that car, oops! How big is that?

Using non-mobile solar cells to produce an energy-dense fuel which is portable makes sense, even if there is an efficiency hit.

Cars themselves are not efficient no matter how they are powered, because utmost efficiency in a car means lying on your back in a narrow, feather-weight, fragile aerodynamic tube with wheels, going about 25 mph max, and taking minutes to get to that speed. Forget niceties like air conditioning.