Effects of PCBM loading and thermal annealing on nanomorphology of blend of polymer/fullerene thin films solar cells: Impact on charge carrier mobility and efficiency.

Blend of P3HT/Fullerene thin films solar cell with two different percentage ratio of PCBM loading is investigated. Optical absorption spectroscopy is employed to elucidate the nature of PCBM cluster formation upon thermal annealing. Sandwich structures comprising of ITO/Cs2CO3/P3HT: PCBM/LiF/Al (electron only device), and ITO/PEDOT:PSS/P3HT: PCBM/Au (hole only device) are fabricated using spin coating for the investigations concerning electron and hole mobilities. The impact of charge carrier mobilities on bimolecular recombination and ultimately the power conversion efficiency for two different PCBM loading is also investigated. A direct correlation between Langevin recombination rate and short circuit current density as a function of thermal annealing is realized. The maximum power conversion efficiency is measured at 150C for P3HT: PCBM (1:1) solar cell.