Roll-to-Roll Printing—A High-Throughput Digital Research Platform for Organic Photovoltaics

Organic Photovoltaics (OPV) are yet to reach market readiness due to their relatively low power conversion efficiencies (PCE). However, the emergence of high-performance non-fullerene acceptors (NFA) has enabled a rapid increase in the PCE of state-of-the-art devices, with the record PCE of over 18 %, which is comparable to that of inorganic counterparts, bringing about a renaissance in OPV technologies. The key advantage of NFA over fullerene-based counterparts is their tunable opto-electronic properties. Energy levels can be tailored for minimum voltage loss and the absorption spectrum can be tuned to be complementary to that of donor materials so the integrated absorption covers a broad range of the solar spectrum. The latter approach can be further expanded by introducing multiple acceptors in so-called ternary or quaternary blend systems. Such an approach provides an opportunity to raise the PCE beyond 20 %, however, it also creates a new challenge in exploring numerous possible material combinations, together with thickness variations, thermal annealing conditions and processing additives. Once a market competitive PCE has been achieved on a laboratory scale, the next step would be translating the technology for commercial manufacturing.<br/>One of the key advantages of OPV is the potential for low-cost manufacturing by industrial roll-to-roll (R2R) printing. However, rapid progress has been driven by material innovations and high PCEs have been demonstrated mostly by laboratory processes on glass substrates using R2R incompatible techniques. The PCEs of R2R OPV devices have been lagging far behind those of laboratory ones. An ideal solution to this problem is to explore the enormous parameter space using a new research method that can quickly screen a large number of parameters using industrial R2R printing methods.<br/>Therefore, an automated R2R research platform has been developed to accelerate OPV research toward commercialization. A programmable<i> in situ </i>formulation system with slot die coating, a lossless deposition method, enabled the fabrication of over 10,000 unique OPV cells in a day with about 150 mg of materials (i.e. 15 µg of donor + acceptor per cell). A R2R testing system, with a matched capacity of over 10,000 tests per day, has also been developed and used to characterize R2R processed OPV devices. This research platform has enabled rapid progress of R2R-printed OPV and the demonstration of 10 % PCE fully-R2R-printed OPV. Despite the progress of OPV with vacuum-deposited metal electrodes, the efficiency of R2R OPV with printed back electrodes have been only up to 7 % and the result represents significant progress from previously reported results. The fabrication parameters and testing results have been digitalized to utilize digital technologies, i.e. artificial intelligence (AI) and machine learning (ML), to analyse such a huge experimental dataset. The research platform is being used to further optimize the formulation and processing parameters. The recent progress of the R2R printed OPV cells, as demonstrated by the fabrication of large-area OPV modules using the digitally optimised manufacturing parameters, will also be presented in the presentation.