During the last two years, the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) could be increased beyond 14% for single and 17.3% for tandem heterojunctions due to the discovery of novel non-fullerene acceptor (NFA) [1, 2]. In the field of NFAs, we have recently studied ternary blend approaches to increase open circuit voltage [3] as well the determination of charge transfer state energies from luminescence spectra in solar cells [4]. As now the performance of NFA based PSCs makes it highly promising as photovoltaic technology for a large number of niche markets, it is important to study aspects such as processing of PSCs with industrial relevant materials and printing techniques. Ink-jet or digital printing is one of the promising techniques. Indeed it allows to generate PSCs controlled in shape and size for niche markets demanding personalized engineering of solar cells. Recently ink jet printing was used to print PSC with high efficiencies [5] still ~5 % and tunability in shape [6]. Improvements in the efficiency can be expected by the usage of novel NFAs family of the ITIC based on indacenodithieno-[3, 2-b]-thiophene, (IDT), usually end-capped with 2-(3-oxo-2, 3-dihydroinden-1-ylidene)-malononitrile [7] in combination with more efficient printable interfacial layers and electrodes. We recently demonstrated that specific formulations of PEDOT:PSS allow to print highly efficient PSC using fullerene based acceptor with efficiency over 6.5% [S. Ben Dkhil, P. Pierron, O. Margeat, J. Ackermann,  patent application submitted 2018, paper in preparation] revealing the high potential of PEDOT:PSS for ink jet printing.

In order to go beyond this efficiency and to benefit from the unique properties of the new generation of non fullerene acceptors, we studied systems consisting of ITIC and ITIC-4F acceptors and PBDB-T and PBDB-T-SF donors towards stable fully solution processed high efficiency OSCs. First we optimized interfacial layers and ink formulation in O-xylene as a “green” solvent  for fully solution processing of PCSs based on NFAs resulting in the PCEs ~11% for the PBDB-T-SF/ITIC-4F system. We show that replacement of MoOx as HTL by PEDOT:PSS in an inverted structures introduce only performance losses from 9.4% for PBDB-T:ITIC to 7.7% making fully printed high efficiency PSCs possible. Finally, we present cells with printed active layers and fully ink jet printed ITIC-4F based solar cells processed in air and evaluate their stability under storage conditions and under illumination compared to devices that were processed by spin coating under Argon. The nanoscale morphology and quality of the ink-jet printed active layers are characterized by STEM and AFM techniques.