Up to date, perovskite solar cells (PSCs) have attracted lots of attention from the research community in the world because its power conversion efficiency (PCE) increased quickly from 3.8% to 23.3% within last seven years.^[1-2] In spite of achieving the world record PCE rapidly, the commercialization of PSCs still remains challenging due to its high production cost and less stability. The main reason is the intensive use of 2,2’,7,7’-tetrakis(N,N’-di-pmethoxyphenylamino)-9,9’-spirbiuorene (Spiro-OMeTAD) as standard hole transporting material (HTM). Although Spiro-OMeTAD based devices achieved a remarkable performance of 21.1%,^[3] there are still some main shortcomings of Spiro-OMeTAD, including high cost and multistep synthesis.^[4-5] Extraordinarily, Spiro-OMeTAD requires additives, which enhance the performance of the device, however, at the cost of stability stability.^[6-7] These bottlenecks can hamper the progress of low cost and large area flexible PSCs.

Recently, the use of inexpensive organic dyes as hole transporting materials (HTMs)as an alternative to Spiro-OMeTAD for perovskite solar cells (PSCs) has paid attention because it paves way for the development of cost-effective and printable solar cells. Currently, the design of HTMs based on anthanthrone (ANT),^[8-9] carbazole (CAZ),^[10-12] diketopyrrolopyrrole (DPP),^[13-14] and isoindigo (IS)^[15] dyes exhibited promising power conversion energy (PCE) in perovskite devices. Among a few dopant-free these dyes-based HTMs, there are several dyes-based HTMs required the additives to enhance the device performance. Though the PCE is enhanced, the presence of these salt dopants leads to the decrease in the stability of the devices and the increase in the cost production. Therefore, the exploration of novel dopant-free organic dyes-based HTMs has been developed.

In this work, we report three novel simple cost efficient solution processable small molecular HTMs based on quinacridone (QA) dye, denoted as ACE-QA-ACE, TPA-QA-TPA, and DPA-QA-DPA. In this design, acenaphthylene (ACE), triphenylamine (TPA) and diphenylamine (DPA) are selected as end-capping groups whereas QA plays a role of the central core. These HTMs were fabricated in mesoscopic TiO₂/CH₃NH₃PbI₃/HTM solid-state PSCs without additives. Under 1 sun condition, the devices achieve the maximum efficiency of 17% for ACE-QA-ACE, 6% for TPA-QA-TPA, and 12% for DPA-QA-DPA. First time, we have used QA dye for making such non-doped HTMs for high-performance Perovskite solar cells. Meanwhile, the reference device with doped Spiro-OMeTAD as HTM showed a PCE of 18%. Most importantly, the unencapsulated devices based on these novel pristine HTMs show impressive stability in comparison with the reference devices. These linear symmetrical HTMs pave the way for new classes of the organic hole transporting materials for cost-efficient and large area applications of printed perovskite solar cells.