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

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/CH₃NH₃Pbl₃/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 V_oc value, tetra substituted CuPc is an appropriate candidate that can replace expensive and unstable HTMs that are currently used in PSCs.