Application of the AMPS computer program to organic bulk heterojunction solar cells

Numerical modeling of organic bulk heterojunction (BHJ) solar cells has been undertaken using the AMPS computer code and material parameters representative of the P3HT/PCBM cell. These simulations show that the V_OC and thus the efficiency of these BHJs is currently controlled by interface recombination. These results show V_OC tracks with the HOMO (D) - LUMO (A) difference with a relationship of the form V_OC = V_I + m[HOMO (D) - LUMO (A)], as is seen experimentally. The AMPS simulations show that the built-in potential and the contact barrier heights surprisingly do not affect V_OC in these cells. These do, however, affect the cell fill factor FF and efficiency. If interface recombination is suppressed, then V_OC values larger than HOMO (D) - LUMO(A) difference are possible since band bending must occur at the heterojunction to sustain the bulk and contact recombination that balances generation at open circuit. With interface recombination suppressed and contacts chosen for optimum FF, this modeling shows BHJs are capable of power conversion efficiencies of about 10% using material parameters corresponding to a P3HT/PCBM cell.