Hydrophobic 4-(isopropylbenzyl)oxy-substituted metallophthalocyanines as a dopant-free hole selective material for high-performance and moisture-stable perovskite solar cells

Abstract

Dopant-free hole-transporting materials (HTMs) are necessary to overcome the instability for perovskite solar cells (PSCs) originating from conventional HTMs such as spiro-OMeTAD requiring hygroscopic dopants for future commercialization. Herein, a series of dopant-free HTMs based on peripherally 4-(isopropylbenzyl)oxy-substituted phthalocyanines with different core metals (EG-pZn1, EG-pCu1, and EG-pNi1) are designed and introduced as a hole-transport layer in PSCs for the first time. The introduction of hydrophobic bulky 4-(isopropylbenzyl)oxy moieties to the phthalocyanine structure favors excellent moisture-resistant effect, and good solubility, as well as suppression of charge recombination in PSCs. Three HTMs-based cells afford an impressive efficiency of 17.60% (EG-pNi1), 16.45% (EG-pCu1), and 15.83% (EG-pZn1) with the character of hysteresis-free. More importantly, while EG-pNi1 and EG-pCu1 HTL-based devices can effectively protect perovskite film from moisture which degraded to only 10% of its initial efficiency under humidity level (60–65%) after a period of 20 days, unexpectedly, ∼30% loss of initial efficiency has been observed in EG-pZn1 HTM based devices under the same conditions. Furthermore, EG-pNi1-based devices also show excellent thermal stability, maintaining 95% initial efficiency after aging for 20 days at 85 °C. These results demonstrate the role of peripherally substituted hydrophobic 4-(isopropylbenzyl)oxy group in HTMs on photovoltaic performance and moisture-/thermal-stability of PSCs and its potential in reasonable and effective ways of industrial commercialization of PSCs.