A solar cell is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect. The term solar cell is reserved for devices designed specifically to capture energy from sunlight while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar modules, also known as solar panels. The energy generated this from solar modules, referred to as solar power, is an example of solar energy. Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight.
High-efficiency solar cells are a class of solar cell that can generate more electricity per incident solar power unit (watt/watt). Much of the industry is focused on the most cost efficient technologies in terms of cost per generated power. The two main strategies to bring down the cost of photovoltaic electricity are increasing the efficiency of the cells and decreasing their cost per unit area. However, increasing the efficiency of a solar cell without decreasing the total cost per kilowatt-hour is not more economical, since sunlight is free. Thus, whether or not "efficiency" matters depends on whether "cost" is defined as cost per unit of sunlight falling on the cell, per unit area, per unit weight of the cell, or per unit energy produced by the cell. In situations where much of the cost of a solar system scales with its area (so that one is effectively "paying" for sunlight), the challenge of increasing the photovoltaic efficiency is thus of great interest, both from the academic and economic points of view. Many groups have published papers claiming possibility of high efficiencies after conducting optical measurements under many hypothetical conditions. The efficiency should be measured under real conditions and the basic parameters that need to be evaluated are the short circuit current, open circuit voltage.