Optimization of photocurrent in bulk heterojunction organic solar cells using optical admittance analysis method

The optimized thicknesses of the active individual layers in organic thin film solar cells are obtained using optical admittance analysis method (OAAM). We have used OAAM to simulate the optical properties of two bulk-heterojunction (BHJ) organic solar cells (OSCs) of structures: (1) ITO/PEDOT:PSS/P3HT:PCBM/Lif/Al and (2) ITO/PTB7:PCBM/Lif/Ag. The optimal thicknesses of 75 nm and 115 nm of P3HT:PCBM and PTB7:PCBM blend layers, respectively, are obtained by maximising the absorbance in these layers through this simulation, which agree very well with the experimental results. The simulated short-circuit current density J_SC is plotted as a function of the active layer thickness for a few selected thicknesses of the Al cathode in these two OSCs and it is found that J_SC becomes maximum when the thickness of Al cathode is 40 nm. Using these optimised thicknesses of the active layers in these two cells the short-circuit current density is found to increase in ITO/PEDOT:PSS/P3HT:PCBM/Lif/Al BHJ OSC by 4.8% and in ITO/PTB7:PCBM/Lif/Ag by 13.3%.