Modelling hole transport in conjugated polymers and blends for solar cell applications

We present Monte Carlo simulations of time-of-flight hole photocurrent transients and of the field and temperature dependence of hole mobility in blends of MDMO-PPV with PCBM and PCBM with polystyrene (PS). Hopping transport is modelled as small polaron tunneling between nearest neighbours in an energetically disordered medium. Hole transport in pristine MDMO-PPV is reproduced quantitatively using a density of states with an exponential tail of trap states. This leads to strong field and temperature dependence. Observed hole transport in PCBM:PS is reproduced with a Gaussian density of states. Finally we investigate whether hole transport in the PCBM fraction of MDMO-PPV:PCBM blends can explain the unexpectedly high hole mobility at PCBM weight fractions over 50%.