Is photosynthesis highly efficient?

One should be careful about comparing apples and oranges!

There is a helpful and interesting article in Science Comparing Photosynthetic and Photovoltaic Efficiencies and Recognizing the Potential for Improvement
written by an Aussie Rules football team (18 co-authors!).

It points out that quantifying the efficiency of photosynthesis is not completely straightforward. It is sometimes claimed that it has evolved to have an optimum efficiency and that it has a quantum efficiency of 100% because every photon that is absorbed produces a desired chemical product. The authors state:

For comparison with PV electrolysis over an annual cycle, the energy efficiency of photosynthesis is a more useful parameter and is defined as the energy content (heat of combustion of glucose to CO₂ and liquid H₂O at STP) of the biomass that can be harvested annually divided by the annual solar irradiance over the same area. Using this definition, solar energy conversion efficiencies for crop plants in both temperate and tropical zones typically do not exceed 1%, a value that falls far below the benchmark for PV-driven electrolysis.

The authors note that the main evolutionary pressure on photosynthetic organisms is that they survive not that they have the optimum thermodynamic efficiency!

If one wants to compare photosynthesis to photovoltaics one should not consider the efficiency of the latter to produce electrical energy but rather chemical energy. The authors suggest an appropriate measure is the efficiency of photovoltaics to produce hydrogen gas from the water splitting reaction.