The power conversion efficiencies (PCEs) of bulk heterojunction organic photovoltaic (OPV) devices have been reported more than 10%. Recently, in our group, we have achieved a PCE of greater than 11% with an inverted device geometry (device area 0.1 cm2) using a ternary blend comprising, an organic donor polymer, small molecule, and PC71BM, as an active layer. However, the device performance of OSC suffers significant drop with the device area scaling up due to sheet resistance of transparent electrode. In this work, we have used a thin layer of metal grid on top of transparent electrode to reduce the sheet resistance. Using this strategy, we fabricated inverted organic photovoltaic devices with an active layer composed of a ternary blend of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b] thiophene-2-carboxylate] (PTB7-Th) and small molecule (BTR)1 as the donors and PC71BM as the acceptor and we have achieved the PCE of greater than 8% for square centimetre active area devices. We also studied the role of metal grid thickness as well as geometry and annealing of active layer on the performance of OSCs.
1. K. Sun, Z. Xiao, S. Lu, W. Zajaczkowski, W. Pisula, E. Hanssen, J. M. White, R. M. Williamson, J. Subbiah, J. Ouyang, A. B. Holmes, W. W. H. Wong, D. J. Jones, Nat. Commun. 2015. (DOI: 10.1038/ncomms7013).
Polymer solar cells (PSCs) have attracted increasing attention due to their inexpensive, flexible, light weight
and large area device fabrication. However, the efficiency of PSCs is still not yet sufficient for large scale
implementation. Many approaches have been proposed to enhance the efficiency of PSCs. In addition to using new
materials and new device structure, the performance of polymer solar cells can also be improved using efficient interface
layer between the electrode and active layer. Here, we studied the effect of MoO3 as an anode interlayer on both small
molecule and polymer photovoltaic cells. Significant improvement has been observed in the performance of PSCs and
the power conversion efficiency (PCE) of the cell with a MoO<sub>3</sub> interlayer can be enhanced by ~15% comparing to the
cells with a PEDOT:PSS interlayer. This improved device performance is attributed to the combined effect of efficient
charge extraction and the reduction in series resistance of device.