text: Flexible organic solar cells (OSCs) based on a blend of low-bandgap polymer donor PTB7-TH and nonfullerene
  small molecule acceptor IEIC were fabricated via a roll-coating process under ambient
  atmosphere. Both an indium tin oxide (ITO)-free substrate and a flexible ITO substrate were employed in
  these inverted OSCs. OSCs with flexible ITO and ITO-free substrates exhibited power conversion
  efficiencies (PCEs) up to 2.26% and 1.79%, respectively, which were comparable to those of the
  reference devices based on fullerene acceptors under the same conditions. This is the first example for
  all roll-coating fabrication procedures for flexible OSCs based on non-fullerene acceptors with the PCE
  exceeding 2%. The fullerene-free OSCs exhibited better dark storage stability than the fullerene-based
  control devices.