Interface Engineering of Perovskite/Hole Transport Layer Using Nano‐Network Formation in Small Molecule–Polymer Blend for Efficient Inverted Perovskite Solar Cells

Abstract

Inserting the interfacial layer adjusts the energy levels between the electrode and the semiconductor, reduces the recombination of charges at the interfaces, and facilitates charge carrier transport. [14-18] Organic conjugated semiconducting materials have been considered promising interfacial materials owing to their ability to control optoelectronic properties through molecular engineering, the possibility of their application in flexible devices, and low-temperature processes generally below 150 °C. [16,19] Small-molecule semiconducting materials have been studied as one of the interface materials based on their advantages of having a well-defined molecular structure and molecular weight, simple purification, and reproducibility between batches compared with organic polymers. [20-22] In particular, metal phthalocyanines and their derivatives have received considerable attention for increasing the efficiency and stability of optoelectronic devices, owing to their high hole mobility, excellent thermal and chemical stabilities, and low cost. [20,23-25] Despite their advantages, unsubstituted phthalocyanines exhibit low solubility; thus, their film formation methods are limited to processes such as thermal evaporation, [26-29] or they require additional synthesis for solution processing. [30-33] Metal-phthalocyanine tetrasulfonic acids (TS-MPc; M = Cu, Ni etc.) are introduced with sulfonate ion groups that induce their high water solubility for solution processing. However, most soluble small molecules, such as TS-MPc, exhibit poor film formation due to their strong molecular interactions in solution. [34] To overcome the problem of poor film formation, one useful technology is the blending of small molecules with other conjugated polymers, which can improve both film uniformity and charge transfer properties through advanced molecular packing. [35-39] Recently, some research groups reported hole transporting layer (HTL) of PSCs with increased the efficiency and stability of the devices by doping TS-MPc into poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS). The main material in the HTL in their devices was PEDOT:PSS using TS-MPc as a good dopant. [38,39] Herein, we are the first to report the nano-mesh structure formation in a TS

Phthalocyanines, porphyrins and other porphyrinoids as components of perovskite solar cells

“…Self-stability was tested storing the unencapsulated devices in ambient air for 336 h. Unlike TS-CuPc and TS-NiPc , which retained about 70% of the initial PCEs, PEDOT:PSS rapidly degraded. 64…”