Effects of carrier mobilities and active layer thicknesses on performance of P3HT: PCBM bi-layer heterostructure organic solar cells

In the designing of organic solar cells, higher mobility of active materials is not necessary for higher power conversion efficiency (PCE) because it simultaneously control recombination rate and concentration of excess charge carriers in active region. In the Shockley equation the effects of charge accumulation due to low carrier mobility is not included. In this work, 1-dimension drift-diffusion numerical analysis with appropriate models has been done and analyzes the effects of charge carrier mobility and device dimension on the J-V characteristics and performance of bilayer heterojunction solar cells. Optimum mobility found for chosen parameters is in the order of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>-10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup>cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/V-s and about 75 nm device thickness with 50 nm junction depth shows highest PCE on assuming constant exciton generation in the donor layer.