Mandelic Acid as an Interfacial Modifier for High Performance NiOx-based Inverted Perovskite Solar Cells

Graphical Small molecule mandelic acid was introduced for the first time as a modification layer in NiO x and perovskite layers in inverted perovskite solar cells. The MAD modified layer can not only reduce the roughness of the NiOx hole transport layer but also interact with the unreacted PbI 2 in the perovskite layer. As a result, MAD enhanced the crystallinity of the perovskite and thus the photovoltaic performance of the device was improved Nickel oxide (NiO x ) inverted perovskite solar cells have been witnessed as promising solar cells because of the low cast, easy fabrication and negligible hysteresis. However, the inferior interface feature of the link NiO x and perovskite layer often causes poor device property and repeatability. Here, Mandelic acid (MAD) is introduced to form a modified layer, which could improve the poor interface properties between perovskite layer and NiO x layer. The contact angel images revels MAD could increase the hydrophobicity and facilitate the growth of perovskite crystal. The X-ray diffraction pattern and Fourier transform infrared spectroscopy have confirmed that the MAD small molecule could interact with residual PbI 2 crystal, leading to better interface contact and high crystallinity. This is further demonstrated by the scanning electron microscopy test of NiO x /MAD/MAPbI 3 film that average grain size is increased from 201.85 nm to 315.17 nm. The space-charge limited current measurement proves the introduction of MAD molecule that result in the decreased trap state density from 3.58×10 15 cm −3 to 2.7210 15 cm −3 . As a consequence, The power conversion efficiency is significantly improved from 14.9% to 18.42% of MAPbI 3 -based devices that retained nearly 80% initial PCE after 50 days in N 2 without encapsulation.