We demonstrate the conjugated polyelectrolytes (CPEs) as efficient hole transport layer (HTL) of polymer solar cells. Replacing poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) with a CPEs with narrow bandgap results in both improvements in device efficiency and stability. In spite of their narrow bandgap, thin CPE films (thickness of similar to 30 nm) enable sufficient light absorption within the active layer. Enhancement of device efficiency is attributed to low surface roughness, high transmittance in visible region, and reduced charge transfer resistance. Compared to the device with PEDOT:PSS, pH neutral nature of CPEs may enhance device stability under ambient condition. (C) 2018 Elsevier Inc. All rights reserved.