Optimization of processing solvent and film morphology to achieve efficient non-fullerene polymer solar cells processed in air†
Polymer solar cells (PSCs) with remarkable power conversion efficiency and processability have been widely reported; however, most devices are processed using halogenated solvents under an inert atmosphere and require post-treatment to achieve optimal film morphology. In this manuscript, we developed efficient PSCs by combining a wide-bandgap conjugated polymer P2F-EHp and non-fullerene acceptors of IT-4F and IT-4Cl, which can be processed with non-chlorinated toluene:o-xylene co-solvent. It is interesting to note that a device based on IT-4Cl presented impressive photovoltaic performance with a power conversion efficiency of about 12%, which does not require post-treatment of solvent vapor annealing. The detailed investigation of film morphology by grazing incidence X-ray scattering and resonant soft X-ray scattering demonstrated that the co-solvent appeared to assist the manipulation of crystal coherent lengths and effectively decrease the phase separation of the corresponding blend films. Of particular importance is that this material system is compatible with the low-cost blade-coating technique using toluene:o-xylene co-solvent and can be processed under ambient conditions without post-treatment. A remarkable power conversion efficiency of 10.1% was achieved by blade-coating the P2F-EHp:IT-4F:IT-4Cl in air, which is slightly higher than that of 9.94% obtained from the spin-coating device processed in nitrogen. The results indicated that this material system is a promising candidate for constructing efficient PSCs toward practical applications.