Solution-Processable Crystalline Platinum-Acetylide Oligomers with Broadband Absorption for Photovoltaic Cells

A series of solution-processable and crystalline platinum-acetylide oligomers containing a thienyl benzothiadiazole thienyl core and oligothiophene alkynyl ligands are synthesized and characterized. X-ray crystallography analysis indicates a two-dimensional arrangement of oligomers through CH-pi interactions in single crystals. These oligomers show two intense and broad absorption bands in the visible spectral region, with the short-wavelength absorption band being strongly dependent on the olieothiophene length. In neat films, all the oligomers form large crystalline domains of several hundred nanometers in size upon thermal treatment and exhibit space-charge limited current (SCLC) mobilities on the order of 10(-5)-10(-4) cm(2) V-1 s(-1). The photovoltaic properties of these oligomers were evaluated by fabricating bulk heterojunction devices with fullerene derivatives (PC61BM and PC71BM) and some of these devices showed high-power conversion efficiencies (PCEs) of up to 3% and a peak external quantum efficiency (EQE) to 50% under AM 1.5 simulated solar illumination. The present work suggests that well-defined platinum oligomers with desirable light-absorbing and self-assembly properties have potential for solution-processed organic photovoltaics.