In 1905, his so-called Wonder Year, Albert Einstein presented a theory of the photoelectric effect. The new idea came in just two lines. However I boldly claim that Einstein’s theory of the photoelectric effect, although crucially correct, was also crucially wrong.
I claim that Einstein talked too much. His intuition was not careful enough, and too tied up with old fashion particles. Quantum Mechanics, one of the inventors Einstein was, questioned the very nature of elementary particles. Einstein imposed, at the outset, a solution, which, I claim, was erroneous.
What Einstein ought to have said is that electromagnetic energy was absorbed in packets of energy hf (h was Planck’s Constant, f the frequency of the light). That explained immediately the photoelectric effect. It was just enough to explain the photoelectric effect.