Making solar cells out of silicon is difficult. There’s plenty of manufacturing steps, many of them at very high temperatures, and you need a high vacuum and a clean room. However, perovskite solar cells–cells made with hybrid organic-inorganic materials in a perovskite crystal structure–are relatively easy to make using wet chemistry involving solvents or vapor deposition.
In theory, silicon solar cells could be 30% efficient, but in reality, 25% seems to be a practical limit with commercial cells typically topping out at 20%. Perovskite cells are nearly that high now, and could be higher by stacking thin layers, each sensitive to different wavelengths of light.
A recent development at the Lawrence Berkeley National Laboratory may lead to even more efficient perovskite cells. Researchers found that certain crystal structures had a much higher efficiency than other structures. The problem now is figuring out how to produce the crystals to increase the prevalence of that structure.