Optimization of Thermalisation Loss in the Quantum Dot Solar Cells using a Finite Element Method

As thermalisation loss is the dominant loss process in the quantum dot intermediate band solar cells (QD-IBSCs), it has been investigated and calculated for a QD-IBSC, where IB is created by embedding a stack of InAs(1-x) Nx QDs with a square pyramid shape in the intrinsic layer of the AlPySb(1-y) p-i-n structure. IB, which is an optically coupled but electrically isolated mini-band, divides the total band gap of AlPySb(1-y) into two sub-band gaps. To obtain the thermalisation loss of AlPySb(1-y)/InAs(1-x)Nx QD-IBSCs, the position and width of IB in the band gap of AlPySb(1-y) should be calculated. The position of IB, which is equal to the first eigen-energy of a unit cell of QD, is obtained by solving the 3D Schrödinger equation with a finite-element method and the width of IB is obtained by the absorption characteristics. Then, with the investigation of the effect of nitrogen and phosphorous molar fraction, QDs size and the  distance between the QDs on the thermalisation loss, the minimized loss for the optimized structure of AlPySb(1-y)/InAs(1-x)Nx QD-IBSCs is obtained