||III-V multi-junction solar cells (MJSC), which consist of different energy bandgap materials to match the solar spectrum, have been used in high concentrated photovoltaic (HCPV) to achieve high solar power conversion efficiency (η). Self-assembled InGaAs quantum dots (QDs) structure is expected to be a good candidate for solar cells capable of absorbing light near 1.0 eV. Furthermore, the energy bandgaps for the QDs can be tuned by changing the material compositions and the dot size. By stacking these QD layers of different energy bandgaps, the optical absorption in the infrared region can be enhanced.|
First, we discuss difference of AMQD and AM+Dwell structure. After Photoluminescence (PL), Electroluminescence (EL) and Photovoltaic characteristics measurement, in asymmetric quantum dots-in-a-well solar cell, the strain effect of self-assembled quantum dots is relieved by form of quantum well. The asymmetric quantum dots-in-a-well solar cell has obtained an conversion efficiency Voc =0.65V, Jsc =17.9 mA/cm2, FF=70.5% and η=8.2%.
The conversion efficiency optimization of AM+Dwell（2×1017 cm-3）is using different solutions such as coating a layer of 100nm SiO2, 100nm ZnO, a double layers of (50nm)Si3N4/(30nm)ZnO, and thinning. The highest conversion efficiency performance of optimizing is Voc = 0.73 V，Jsc = 27.4 mA/cm2，FF=75 %，η=15.0 %。
For the Dwell structure, p-type doping concentration is changed by doping Be for 2×1016 cm-3, 2×1017 cm-3, 2×1018 cm-3 respectively. After comparison of photoelectrical properties and solar cell performance ,the dopant concentration of 2×1017 cm-3 has shown the optimal characteristics with a Voc = 0.73 V, Jsc = 27.4 mA/cm2, FF=75 % and η=15.0 %.
Finally, the optimized result of various methods is examined using concentration I-V measurement under simulated solar light of 10 to 100 suns. While increasing concentration suns, the photo-generate current enhances along with the number of photons increases, thus, the open-circuit voltage and the current coefficient is proportional to the light. At concentration of 80 suns, Voc = 0.88 V，Jsc = 2000.7 mA/cm2，FF=81 %，η=17.83 %, with conversion efficiency improvement of 59% compare to former.