Theoretical possibilities of InxGa1-xN tandem PV structures

• Published in: Solar energy materials and solar cells Vol. 87; no. 1-4; pp. 595 - 603
• Main Authors: HAMZAOUI, Hasna, BOUAZZI, Ahmed S, REZIG, Bahri
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Amsterdam Elsevier 01.05.2005
• Subjects: Applied sciences; Energy; Equipments, installations and applications; Exact sciences and technology; Natural energy; Photovoltaic conversion; Solar cells. Photoelectrochemical cells; Solar energy; Short circuit currents; Output power; Photovoltaic system; Solar spectrum; p n junction; Layer thickness; Modeling; Open circuit voltage; Solar cell; Energy gap; Simulation; InGaN; Nickel; Current density; Peak power
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2004.08.020

We designed a model of InxGa1-xN tandem structure made of N successive p-n junctions going from two junctions for the less sophisticated structure to six junctions for the most sophisticated. We simulated the photocurrent density and the open-circuit voltage of each structure under AM 1.5 illumination in goal to optimize the number of successive junctions forming one structure. For each value of N, we assumed that each junction absorbs the photons that are not absorbed by the preceding one. From the repartition of photons in the solar spectrum and starting from the energy gap of GaN, we fixed the gap of each junction that gives the same amount of photocurrent density in the structure. Then we calculated the current density accurately and optimized the thicknesses of p and n layers of each junction to make it give the same output current density. The evaluation of ni: the intrinsic concentration permitted to calculate the saturation current density and the open-circuit voltage of each junction. Assuming an overall fill factor of 80%, we divided the output peak power by the incident solar power and obtained the efficiency of each structure. The numerical values for InxGa1-xN were taken from the relevant literature. The calculated efficiency goes from 27.49% for the two-junction tandem structure to 40.35% for a six-junction structure. The six-junction InxGa1-xN tandem structure has an open-circuit voltage of about 5.34V and a short circuit current density of 9.1mA/cm2.