In particular, the incorporation of either InAs or GaSb quantum dots (QDs) into the GaAs region of a triple junction cell extends the absorption of the device out into the near infra red and consequently enables more efficient capture of the solar spectrum by the creation of new energy states. The wealth of optical and electrical properties of III-Vs coupled with the atomic layer by atomic layer synthesis of the materials using molecular beam epitaxy (MBE) opens the way for further improvements in cell efficiency and cost reductions. In recent years GaAs-based multi-junction cells have demonstrated impressive efficiencies breaking the 40% barrier. The use of anti-reflective coating as well as transparent contacts and its effect on the EQE will be discussed.Ībstract = "Solar cells based on III-V compound semiconductor materials are excellent candidates for renewable, clean electricity generation. The doped 8x1010 /cm2 samples showed the highest efficiency of ~10 %, which is an excellent value for this simple structures. The QD device efficiencies were calculated and are shown in Table 1. The presented Voc value is suitable for solar cell efficiency improvement. The I-V characteristics under light were obtained using a 100mW/cm2 power light showing that the Voc of the n-doped material was extended up to the value of 0.8 volts but at the expense of a reduction of the short-circuit current (Isc), which was reduced to 15.6 from ~20mA/cm2. The doped samples exhibited lower EQE compared to the undoped one, which had a maximum EQE of 40%. The external quantum efficiency (EQE) of the devices were measured under arrange of conditions. Simple cylindrical diodes without any anti-reflection coating or attempts at reducing shadow effects from the contacts were fabricated and tested for both undoped and n-doped structures. The different structures were characterized by Double Crystal X-Ray Diffraction and showed high quality materials, while C-V measurements revealed no noticeable deep traps. Photoluminescence studies show that due to insertion of QDs into the host lattice (x20) two more energy states (1.37 and 1.2 eV) were generated in addition to the 1.4 eV (GaAs bandgap) energy state. In this work several GaAs/InAs quantum dots (QDs) structures were grown on GaAs substrate using Molecular Beam Epitaxy and having different doping profiles (0, 8x1010 and 16x1010 /cm2 in between the dots). The key challenge, thus, is the growth of QDs based materials with expanded absorption spectrum and high open circuit voltage (Voc). The doping of such structures has also proved to enhance the open-circuit voltage which in turn increase the device efficiency. Solar cells based on III-V compound semiconductor materials are excellent candidates for renewable, clean electricity generation.
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