Design of charge transporting grids for efficient ITO-free flexible up-scaled organic photovoltaics
Successfully transferring the device efficiency of small area organic solar cells (SA-OSCs) to a large scale area is a tough challenge. The charge collecting and transporting grids are demonstrated to be effective at addressing this issue, and are widely used in commercial silicon solar cells. However, appreciable shadow loss (5–10%) can be caused with these grids. Thus, a rational design of the grid structure to reduce this significant shadow loss is highly desired. Here, we show that the significant energy loss on scaling up the OSC area stems from the accumulated current density along the charge transport direction. Accordingly, a rational pattern of shorter and triangular Ag grids is designed to accommodate the accumulated current density, leading to a high efficiency of 6.93% for up-scaled OSCs of 4 cm2.