Conjugated oxazole-based interfacial materials for efficient and stable inverted polymer solar cell with an efficiency of 16.52%

Organic solar cells (OSCs) using non-fullerene acceptors have delivered the highest efficiencies in the overall reported literatures. In order to improve the efficiency and stability of OSCs, great efforts are being made in designing and synthesizing new materials. Inverted OSCs were fabricated using three commercially available and inexpensive materials, 5-methylbenzoxazole (E1), 2-(4-biphenyl)-5-phenyloxazole (E2), and 4-bis(5-phenyl-2-oxazolyl)benzene (E3), as an interlayer between zinc oxide and the active layer. The new interlayer materials enhance the carrier injection/extraction properties and thus, the polymer solar cells (PSCs) exhibited an improved J_SC and power conversion efficiency (PCE). PSCs showed an improved J_SC of 27.18 from 24.88 mA/cm² with the introduction of E3. The new interlayer, E3 in particular, forms well-aligned cascading energy levels between the PM6:Y6 active layer and zinc oxide layer. These cascading energy levels reduce the energy barrier for electron injection and collection at the interface. Thus, the PCE of devices reached a remarkable 16.52% using interlayer at the ZnO/active layer interface. The devices also exhibited improved device stability under continuous illumination, annealing, and high humidity.