Top-illuminated organic photovoltaic cells with slot die coating of functional layers processed in ambient conditions

Abstract Printed organic photovoltaic (OPV) devices are well-suited for high-throughput manufacturing, enabling large volume and low-cost production. The printing processes that are typically available are for OPV device stacks built on transparent substrates, where the devices are illuminated from the substrate (bottom) side. These device stacks, however, will not be suitable for building OPV on opaque substrates, because for opaque substrates the devices need to be illuminated from the top (away from the substrate) side. Moreover, many opaque substrates, which are rough, will need to be first coated with a smoothening layer before OPV devices can be fabricated on them. In this work, a predominantly slot die coated (SDC) device stack that would be needed for a rough opaque substrate, such as commercially available paper, is developed. The total stack consisting of a polyvinyl formal (PVF) smoothening layer; silver (Ag) bottom electrode; zinc oxide (ZnO) electron transport layer; a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) as the photoactive layer; and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the top hole transport layer cum transparent conducting anode layer has been developed on top of glass substrates. The PVF layer is doctor blade coated; Ag is vacuum thermal deposited; and the other primary layers in the stack are all coated with slot die. The SDC devices showed a best power conversion efficiency of 2.35% under AM1.5 G, 1 sun, and 5.25% under indoor 10 000 lux cool-white LED illumination. These values are in the ballpark of the performance of similar devices fabricated by spin coating of the primary layers for ‘top-illuminated’ P3HT:PCBM control devices. The process developed here should facilitate SDC-based fabrication of OPV on substrates such as commercial paper or steel.