A Novel pH Neutral Self-Doped Polymer for Anode Interfacial Layer in Efficient Polymer Solar Cells

Three pH neutral conjugated polymers based on thiophene and benzene derivatives, namely PCP-Na, PCF-Na, and PFS-Na, were designed and synthesized. In the three polymers, PCP-Na exhibited a self-doping effect in aqueous solution, and the thin film of PCP-Na demonstrated a high electrical conductivity of 1.66 × 10–3 S/cm and a deep HOMO level of −5.22 eV; these properties make it an ideal anode interfacial layer (AIL) material in polymer solar cells (PSCs). The single-junction PSC modified with PCP-Na AIL showed a PCE of 9.89%, which is comparable to that of the PEDOT:PSS-modified device (PCE = 9.53%). Notably, PCP-Na AIL exhibited excellent thickness insensitivity in fabricating PSC devices; i.e., the PSC devices with very thick PCP-Na interlayers over 300 nm still demonstrated a high fill factor over 70%, indicating the PCP-Na layer has excellent charge collection and transport properties. Furthermore, the homo-tandem PSC device was fabricated using a new connecting interlayer, which consists of PCP-Na as the hole collection layer and ZnO as the electron collection layer, and a PCE of 10.54% was achieved in the homo-tandem device.