Tetra and octa substituted Zn(II) and Cu(II) phthalocyanines: Synthesis, characterization and investigation as hole-transporting materials for inverted type-perovskite solar cells

Abstract

Metallophthalocyanines (MPcs) are used as cost-effective and thermally stable hole-transporting materials (HTMs) in the production of perovskite solar cells (PSCs). Unlike the mostly used n-i-p type PSCs, there are a few studies based on p-i-n type PSC with pthalocyanine HTMs. Here, for the first time, both tetra and octa substituted zinc and copper phthalocyanines have been studied as hole transporting materials in the inverted-type (p-i-n) PSCs without using any dopant material. The developed tetra substituted ZnPc and CuPc possess four dichlorophenylthio groups, and the octa-substituted Pcs have eight dichlorophenylthio groups in their peripheral position which enhance their solubility in perovskite-friendly solvent and improved thin film quality. In the inverted solar cell (ITO/HTM/CH(3)NH(3)Pbl(3)/PCBM/Al), methylammonium lead iodide (MAPI) was used as the active layer and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as the electron transport material. Devices based on tetra substituted zinc and copper Pcs, as dopant-free HTMs, indicated significant efficiency enhancement and cell stability compared to similar octa substituted Pcs. While the open-circuit voltage (V-oc) for the reference PEDOT:PSS was measured 0.77 V, for tetra substituted CuPc was found to be 0.83 V. Due to higher Voc value, tetra substituted CuPc is an appropriate candidate that can replace expensive and unstable HTMs that are currently used in PSCs.