Lattice-Matched III–V Dual-Junction Solar Cells for Concentrations Around 1000 Suns

Concentration photovoltaic (PV) based on III–V solar cells is one of the most promising technologies for dramatically reducing the cost of PV electricity. In order to reduce costs, a high efficiency is usually pursued. This is the main reason for the huge development of multijunction cells (MJCs) which are able to achieve very high efficiencies thanks to their more efficient use of the solar spectrum. In the first stage, our approach to reduce the cost of photovoltaic electricity consists of a further development of the lattice matched $GaInP∕GaAs$ dual junction solar cell in order to achieve efficiencies of over 30% at 1000 suns (AM1.5D low aerosol optical depth (AOD)). In the second stage, this approach will allow us to develop lattice matched $GaInP∕Ga(In)As∕Ge$ triple junction solar cells with higher efficiency and lower cost. In this technical brief, we have set out the philosophy, including a brief incursion into economics, and our first results of dual-junction solar cells for high concentrator applications. Our best result is an efficiency of 27.6% at 180 suns while at 1000 suns the efficiency is 26% (AM1.5D low AOD). The price of a PV installation based on our best solar cell to date (efficiency of 26% operating at 1000 suns) would be $3.6$∕Wp$⁠. For solar cells with efficiencies of 30% at 1000 suns, the price after a cumulated production of $10MWp$ of a PV installation would be $3.3$∕Wp$⁠. The efficiencies attained $(∼26%)$ at 1000 suns although still far from our objective of 30%, establish a reasonable starting point for future developments. It is evident that the conservative design implemented has much room for improvement which is now under development in our lab.