Toxic Solvent- and Additive-Free Efficient All-Polymer Solar Cells via a Simple Random Sequence Strategy in Both Donor and Acceptor Copolymer Backbones

It is extremely important to develop nontoxic solvent and additive-processed high-performance all-polymer solar cells (all-PSCs) that are suitable for printing preparation of large-scale devices. Herein, it is demonstrates that a simple random copolymerization of two acceptor monomers (benzo[1,2-c:4,5-c ']dithiophene-4,8-dione (BDD) and 5,6-difluoro-2H-benzo[d][1,2,3]triazole (FTAZ)), alternating with Si atom-containing benzo[1,2-b:4,5-b ']dithiophene donor comonomer, forms a successful approach by which to synthesize donor copolymers with excellent solubility/processability for nontoxic-solvent-processed all-PSCs. The incorporation of a higher degree of BDD in the backbone lowers the frontier energy levels, as well as redshifts, with higher absorption coefficients; however, it adversely affects solubility in a 2-methyltetrahydrofuran (MeTHF). An impressive power conversion efficiency, of about 8.0%, is achieved from PJ25 (25 mol% BDD)-based all-PSC when paired with N2200-F30 acceptor random copolymer by using MeTHF as the processing solvent without any additive. Another interesting point is that the air stability of the all-PSCs increases with increasing FTAZ content due to strong noncovalent interaction and resistance to humidity and oxidation caused by the F-atoms in FTAZ units. Not only does this study establish a structure-property-performance relationship through a series of structural, morphological, and electrical characterization techniques, but it also provides a promising and easy way to develop nontoxic-solvent-processed high-performance all-PSCs.