As with any energy conversion process, there is a physical limit for the photovoltaic conversion process. The theoretical maximum efficiency for a crystalline silicon solar cell – a commonly used type of solar cell – is about 29 percent. The theoretical maximum is the best case scenario under perfect conditions. To date, crystalline silicon cells have only reached about 25 percent efficiency in the laboratory, and 22 percent in commercialized panels.
Higher theoretical (and real-world efficiencies) can be attained by concentrating light or stacking multiple photovoltaic materials on top of one another to capture more energy across the light spectrum. The latter approach results in what are called multijuction cells. According to some estimates, two junctions cells have a maximum efficiency of 43 percent; three junction cells at 49 percent, and an infinite number of junctions could theoretically reach 68 percent efficiency at normal light concentrations. If the light were concentrated, a cell with infinite junctions could attain 87 percent efficiency theoretically. To date, a four junction multijunction cell with concentrated light has reached about 45 percent efficiency in the laboratory.
Thin film cells, multicrystalline silicon, and emerging solar cell types currently have lower efficiencies in the laboratory, though some of these emerging cells (e.g. perovskite, organic, and quantum dot cells) have seen great increases in efficiencies over just a short period of time.