Increasing Stability of SnO2-Based Perovskite Solar Cells by Introducing an Anionic Conjugated Polyelectrolyte for Interfacial Adjustment.

Despite the fact that power conversion efficiency (PCE) has been greatly improved in recent years, perovskite solar cells (PSCs) need to overcome some challenges, like stability, for the commercial application. Herein, an anionic conjugated polyelectrolyte, sulfonic-containing polyfluorene (abbreviated to SPF), has been developed to modify the interface between the electron-transporting layer (ETL) SnO2 and the optoelectronic active layer MAPbI3 in the n-i-p cells. After 40 days of storage in atmospheric environment in the dark with exposure to a controlled humidity of about 10%, PCE of the SPF-modified cells with the structure of ITO/SnO2/SPF/MAPbI3/spiro-OMeTAD/Au still remained 94% of the initial value. In contrast, the control cell without SPF only remained 31.1% of its initial efficiency after 29 days. The main reason for the stability enhancement is the adjustment of interfacial energy level, the crystallinity enhancement, and the removal of the interfacial defect of the perovskite layer by introducing the hydrophobic and smooth SPF interfacial layer. Deep electrical study on the PSCs discloses that the cell has low carrier transfer resistance, low leakage current density, and minor interfacial charge accumulation. What's more, the short-circuit current density is improved, and PCE of 20.47% is achieved.

1,8-Substituted Pyrene Derivatives for High-Performance Organic Field-Effect Transistors.

There have been many reports on the application of pyrene derivatives as organic semiconductors, but 1,8-subsituted pyrene semiconductors are less well-developed. Two p-type 1,8-substituted pyrene derivatives were synthesized that were composed of a pyrene core, thiophene or bithiophene arms, and end-capped octyl chains. These structures were not completely symmetrical and the dihedral angles between the pyrene core and the adjacent thiophene units had a difference of approximately two degrees. The field-effect performance of these materials was tested on a variety of dielectric surfaces. The performance of both materials with a spin-coated polystyrene layer on SiO2 (PS-treated SiO2 ) was better than that with an octadecyltrichlorosilane self-assembled monolayer on SiO2 (OTS-treated SiO2 ), which was mainly attributed to the presence of large grains on the low-leakage and high-capacitance PS films. The thiophene-contained compound presented a hole mobility of up to 0.18 cm2 V-1 s-1 on PS-treated SiO2 , which was 45 times that of the bithiophene-contained compound, owing to less steric hindrance, high crystallinity, and large grain size.