People have been using the sun as an energy source for hundreds of years, but the history of the modern solar cells trace back to the late 1800s. Back in 1839, a then-19-year-old Alexandre-Edmond Becquerel, a French physicist known for his work in light-based fields, discovered the photovoltaic effect. Becquerel found that when he placed silver chloride into an acidic solution, it was able to produce an electric current and voltage when exposed to light. The result was weak, but instrumental to the technology we see today.
In 1883, the first photovoltaic cell was built by Charles Frittz. It was impressive, but still could only able to convert ~1% of absorbed sunlight into power. The field of solar cells would slowly, slowly improve over the coming decades: Russell Ohl, an American engineer, patented the first photovoltaic cell in 1946 and Bell Laboratories made first silicon cells less than a decade later in 1954. Unlike any previous cells, the ones made by Bell Laboratories had a whopping 6% efficiency rating when it came to converting sunlight into power. By the early 60s, silicon cells could boast up to a 14% efficiency rating, but no more.
This invention helped boost the popularity of solar cells, but cost was a major hinderence. Cells made in the 50s and 60s cost almost $300 per watt and so were regulated to two opposite extremes: very small cells for toys and much larger cells for major projects (usually military or space).
From there, solar technology continued to develop, though still at a slow pace. Even with all its progress, most solar cells still cost $100 per watt. Not too appealing without more power behind it. In 1985, rigid solar cells are able to convert 20% of absorbed sunlight into power, while thin film cells hover at about half that efficiency. Solar cells would experience another boost in efficiency in the early 90s, with thin film cells converting at ~16% efficiency and ridgid cells breaking into the 30% range. As the technology improved further, the idea of "$1 per watt" became the new level to strive for.