Recombination Dynamics as a Key Determinant of Open Circuit Voltage in Organic Bulk Heterojunction Solar Cells: A Comparison of Four Different Donor Polymers - Maurano,A; Hamilton,R; Shuttle,CG; Ballantyne,AM; Nelson,J; O'Regan,B; Zhang,W; McCulloch,I; Azimi,H; Morana,M; Brabec,CJ; Durrant,JR (ADVANCED MATERIALS, 2010)