Terpolymer acceptors based on an organic ligand or corresponding cyclometalated Pt complex for all polymer solar cells

Two series of terpolymers were synthesized by embedding certain amount (1, 5 or 10 mol%) of cyclometalated PyTPAPt(acac) complex or the corresponding organic PyTPA ligand into famous copolymer PNDIT2 backbone. Comparable optical and electrochemical properties were obtained for terpolymers compared with copolymer PNDIT2. When fabricated in all polymer solar cells (all-PSCs) with PTB7-Th donor, the control PNDIT2 copolymer acceptor exhibited a maximum power conversion efficiency (PCE) of 2.58%. Interestingly, the PCE variation demonstrated unexpectedly distinguished trends in terpolymers with or without Pt center. Gradually increased PCE from 2.55 to 2.89 and 3.26% was attained by employing Pt-containing terpolymer PPyTPAPt1, 5 and 10 as acceptor. In contrast, gradiently decreased maximum PCE from 2.52 to 2.31 and 1.88% were obtained for terpolymer acceptor of PPyTPA1, 5 and 10. Through a combination of photoelectric measurements, enhanced exciton dissociation rate, suppressed charge recombination, higher carriers mobilities and more efficient charge transfer were observed in Pt-based devices. Notably, no triplet absorption behavior was detected in Pt complex-containing devices from transient absorption spectra. And the variations on the photovoltaic properties were illustrated by the fine-tuned polymer crystalline behaviors through grazing-incident wide-angle X-ray scattering (GIWAXs) measurements. Compared with the control copolymer PNDIT2 blends, Pt-containing terpolymers induced a reduced crystalline feature with weaker π-π and lamellar stacking, while tepolymers without Pt-center demonstrated over-strong crystallization.