Low cost and solution-processable zinc phthalocyanine as alternative hole transport material for perovskite solar cells†
Metal phthalocyanines (MPcs) as an important class of organic semiconductors or hole transport materials (HTMs) have been extensively used in organic solar cells. Nevertheless, most of them are highly insoluble and need to be processed through a strict high-vacuum deposition process. Herein, a solution-processable tert-butyl substituted zinc phthalocyanine (hereafter referred to as ZnPc(tBu)4) with relatively high hole mobility and favorable HOMO and LUMO levels has been synthesized and employed as dopant-free HTM layer in methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs), and the corresponding ZnPc(tBu)4-based PSCs after optimizing the ZnPc(tBu)4 concentration achieved a power conversion efficiency (PCE) of 5.16% and 7.98% measured under forward and reverse voltage scanning, respectively. The unsatisfactory photovoltaic performance of ZnPc(tBu)4-based PSCs compared to the classical spiro-OMeTAD-based ones can be mainly due to the very low fill factor and severe hysteresis, which would be eliminated by further optimizing the device fabrication procedure and the interfacial contacts between the mesoporous TiO2 film and MAPbI3 overlayer, and thus the present solution-processable and dopant-free ZnPc(tBu)4 would be a potential substitute for the expensive HTMs containing multifold additives used in the current PSCs.