Green solvent-processed organic solar cells based on a small-molecule Ir(iii) complex as electron donor materials

Small-molecule octahedral cyclometalated Ir(iii) complexes as photoactive materials have attracted specific attention in organic solar cells (OSCs) due to the potential utilization of triplet excitons. Different from previous work on the design of new Ir complexes, herein, we developed an effective device optimization strategy through the synergistic involvement of environmentally friendly solvents and high-temperature spin-coating process, thus a record-high power conversion efficiency (PCE) of over 12% for small-molecule Ir(iii) complex based OSCs was achieved. Processing solvents with different boiling points (BP), namely halogenated chloroform (CF), 1,2-dichlorobenzene (DCB), and non-halogenated o-xylene (XY), were selected for OSCs based on the TBz3Ir donor and PY-IT polymer acceptor. Both film morphologies and photovoltaic performances were nearly insensitive to the processing temperatures when low BP CF was used, with average PCE maintained at ∼8.5%. Differently, the aggregation behavior could be suppressed for the TBz3Ir:PY-IT blended films when processed using high BP XY and DCB at higher temperatures. Therefore, enhanced PCE from 5.25 to 12.04% for XY and 5.22 to 7.82% for DCB processed devices were achieved by increasing the spin-coating temperature from 25 °C to 90 °C. The best performance for XY at 90 °C processed devices came from the improved active layer film morphology with proper phase-separated bicontinuous interpenetrated networks for improved exciton dissociation, reduced charge recombination, and improved charge transport.