Though just about every solar cell you see today utilizes silicon, the photoelectric effect is present and strong in many materials. Some of these materials offer advantages to silicon, such as being cheaper to produce and responsive to a greater amount of light. One class of materials, quantum dots, has particularly peaked researchers', including those at MIT who have recently developed a better cell using them.
Quantum dots are specially designed semiconductor crystals which can be made to react to any frequency of light; a powerful property for any solar cell. Unfortunately a quantum do solar cell, like all solar cells, need to strike a careful balance between thickness and conductivity. Thicker solar cells are able to convert more light into electricity, but the thickness of the material means less of the electrical current escapes to do anything useful. The researchers have found a way overcome this though by growing a forest of nanowires, with quantum dots interspersed within. As the dots created an electric current, it was easily able to jump to a nearby nanowire and be of use.
This design allowed the thickness and conductivity of the solar cell to be decoupled, ultimately enabling it to reach 5% efficiency. That may not seem high, especially as 10% is considered the minimum for a commercially viable cell, but it is a record for this specific kind of cell, and with optimizations, it could be pushed much higher.