Enhanced power-conversion efficiency in polymer solar cells using an inverted device structure

Polymer-fullerene bulk heterojunction solar cells (PSCs) are currently attracting a great deal of attention and gaining increasing importance, having already shown great promise as renewable, lightweight and low-cost energy sources(1-4). Recently, the power-conversion efficiency of state-of-the-art PSCs has exceeded 8% in the scientific literature(5). However, to find viable applications for this emerging photovoltaic technology, further enhancements in the efficiency towards 10% (the threshold for commercial applications) are urgently required(6). Here, we demonstrate highly efficient PSCs with a certified efficiency of 9.2% using an inverted structure, which simultaneously offers ohmic contact for photogenerated charge-carrier collection and allows optimum photon harvest in the device. Because of the ease of use and drastic boost in efficiency provided by this device structure, this discovery could find use in fully exploiting the potential of various material systems, and also open up new opportunities to improve PSCs with a view to achieving an efficiency of 10%.