It is possible to tailor the band gap of the strain-balanced quantum well solar cell to match the local solar spectral
conditions by altering the quantum well depth. This has led to a recent single-junction world-record efficiency of 28.3%,
as well as giving advantages for current matching in multi-junction solar cells. Radiative recombination is the dominant
loss mechanism for the strain-balanced quantum well solar cell, so practical improvements focus on techniques for light
management in the cell, such as enhancing the optical path length with epitaxial mirrors. Furthermore, the compressive
strain in the quantum wells suppresses emission into TM-propagating modes, reducing the overall optical loss and
increasing the cell efficiency. As biaxial strain can only be engineered into a cell on the nanoscale, quantum well solar
cells are seen to have a fundamental efficiency advantage over bulk semiconductor cells.
Incorporating quantum wells into multi-junction III-V solar cells provides a means of adjusting the absorption
edge of the component junctions. Further, by using alternating compressive and tensile materials, a strain-balanced
stack of quantum well and barrier layers can be grown, defect free, providing absorption-edge / lattice
parameter combinations that are inaccessible using bulk materials. Incomplete absorption in the quantum wells
has been addressed using a distributed Bragg reflector, extending the optical path length through the cell and
enabling photon recycling to take place. State of the art single-junction quantum well solar cells have now
reached an efficiency of 27.3% under 500X solar concentration and are projected to reach 34% in a double
Luminescent concentrator (LC) plates with different dyes were combined with standard multicrystalline silicon solar cells. External quantum efficiency measurements were performed, showing an increase in electrical current of the silicon cell (under AM1.5, 1 sun conditions, at normal incidence) compared to a bare cell. The influence of dye concentration and plate dimensions are addressed. The best results show a 1.7 times increase in the current from the LC/silicon cell compared to the silicon cell alone. To broaden the absorption spectrum of the LC, a second dye was incorporated in the LC plates. This results in a relative increase in current of 5-8% with respect to the one dye LC, giving. Using a ray-tracing model, transmission, reflection and external quantum efficiency spectra were simulated and compared with the measured spectra. The simulations deliver the luminescent quantum efficiencies of the two dyes as well as the background absorption by the polymer host. It is found that the luminescent quantum efficiency of the red emitting dye is 87%, which is one of the major loss factors in the measured LC. Using ray-tracing simulations it is predicted that increasing the luminescent quantum efficiency to 98% would substantially reduce this loss, resulting in an increase in overall power conversion efficiency of the LC from 1.8 to 2.6%.