Why do solar cells need an inventor?

In 1839 Alexandre Edmond Becquerel discovered the photovoltaic effect which explains how electricity can be generated from sunlight. He claimed that “shining light on an electrode submerged in a conductive solution would create an electric current.” However, even after much research and development subsequent to the  discovery, photovoltaic power continued to be very inefficient. People mainly used solar cells for the purpose of measuring light.

Over 100 years later, in 1941, Russell Ohl invented the solar cell, shortly after the invention of the transistor.

where's the diagram?

he would use the colour black