Efficiency of Organic Conjugated Polymer/C$_{60}$ Bulk Heterojunction Photovoltaic Devices

We investigate the influence of thin-film morphology on the efficiency of organic conjugated polymer/C$_{60}$ bulk heterojunction polymer photovoltaic devices. Blends of soluble derivatives of fullerenes (PCBM- C$_{60}$) as electron acceptors and MEH-PPV or [MEH-PPV]-biphenylene-vinylene copolymer as donors are used in the fabrication the ITO/PEDOT:PSS/Polymer Blend/LiF/Al photocells. Thermal annealing effects on the phase segregation within the active layer are probed by scanning electron and atomic force microscopies. The micro/nano-structure morphologies are systematically correlated with the electrical and optical properties of the devices by current-voltage, capacitance- voltage, photocurrent, and electroabsorption spectroscopies. The implications of these results on the optimization of the open-circuit voltage, short-circuit current, and efficiency of the polymer photovoltaic devices will be explored.