Small molecular material as an interfacial layer in hybrid inverted structure perovskite solar cells

Hybrid halide perovskites are becoming increasingly popular due to their immense potential to be used as a low cost and easily processable solar cell technology. Interfacial engineering is believed to be one of the crucial ways to improve the device performance. In this work, we report the introduction of a small molecular interfacial layer 4,4'-(naphthalene-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (TPA-NAP-TPA) between the traditional hole transporting layer poly (3,4-ethylenedioxythiophene:polystyrene sulfonate) (PEDOT:PSS) and perovskite (Cs(0.15)FA(0.85)PbI(3)) active layer. Systematic investigations indicate that the incorporation of the small molecular interfacial layer improves the inverted device efficiency by 7% relative. The crystallinity and morphology of the perovskite formed on top of the PEDOT:PSS/TPA-NAP-TPA is favourable compared to the perovskite formed on top of pristine PEDOT:PSS layer. The improvement in the PCE is attributed to increased photocurrent generation. The devices containing the interfacial layer has also depicted improved quantum yield which is in line with the maximised average JSC. Furthermore, the devices with PEDOT:PSS/TPA-NAP-TPA interfacial layer retained 60% of their initial efficiency after 30 days, which is 30% higher than the devices with pristine PEDOT:PSS layer. Including interfacial layers such as TPA-NAP-TPA could be a viable technique in order to enhance the performance and stability of inverted structure perovskite solar cells.