An inverted polymer photovoltaic cell with increased air stability obtained by employing novel hole/electron collecting layers

In this work, an inverted device was fabricated using titania (TiO2) as the electron collecting layer (ECL) and sulfonated poly(diphenylamine) (SPDPA) as the hole collecting layer (HCL). Smooth TiO2 film with good electron collecting ability was easily formed using the spin-coating process. The power conversion efficiency (PCE) was 3.91%, the same as that of a conventional device. This inverted device is ascertained to maintain 2.82% PCE after 400 h of air-storage. Because of the appropriate work functions of ECL and HCL, the interfaces at the active layer have the ohmic contacts those approach the ideal value of open circuit voltage. SPDPA helps improve the interfacial dipole effect between the active layer and the metal, as verified by in-situ ultraviolet photoelectron spectroscopic data.