Anode Engineering with pH-neutral Conjugated Polyelectrolyte Enabling over 19% Efficiency in Organic Solar Cells

The lack of effective hole-transporting layers (HTLs) materials has become a significant bottleneck in the advancement of organic solar cells (OSCs). Particularly, to obtain sufficient doping property, most HTLs have to be used by mixing with substantial amounts of acid, which causes serious corrosion problems. Herein, by optimizing molecular conformation, we designed and synthesized two conjugated polyelectrolytes (CPEs) that exhibited superior hole-transporting capability without involving the addition of acid. The PEP-BT features a planar conjugated backbone constructed from non-fused segment, which leads to an enhanced doping effect, highly ordered molecular arrangement and reduced π-π stacking from 4.13 Å to 3.85 Å. These contributed to the outstanding hole collection performance of polyoxometalate-doped PEP-BT:POM while maintaining a neutral pH. The binary OSC showed a photovoltaic efficiency of 19.16%, demonstrating an unprecedented example that a CPE-based HTL can provide a photovoltaic efficiency exceeding 19% in OSCs. Moreover, as an another evidence of high-performance HTL, the organic light-emitting diode by incorporating PEP-BT:POM exhibited a superior luminous efficiency to the reference device, along with a decrease of 0.4 V for turn-on voltage. The results from this work demonstrates the great potential of CPEs as high-performance HTL materials.