ARTICLE Journal Name Please do not adjust margins Please do not adjust margins Please do not adjust margins Please do not adjust margins Received 00th January 20xx, Accepted 00th January 20xx DOI: 10.1039/x0xx00000x Impact of Fluorine atoms on triphenylamine-based dopant free hole selective layer for perovskite solar cells Abolfazl Ghaderian, a Meenakshi Pegu, a Naveen Harindu Hemasiri, a Peng Huang, a Shahzada Ahmad, a,b* Samrana Kazim a,b* For industrial endeavors, perovskite solar cells (PSCs) demand long-term stability and a cost-effective hole-transporting layer (HTL). The PSC stability can be substantially improved by the rational design of dopant-free HTL that possesses inherent electrical merits. Further, through molecular engineering by placing a fluorinated arm on an established triphenylamine core, superior stability can be achieved, while using cost-effective precursors and easy synthesis routes. Here we developed fluorinated triphenylamine-based HTL, and probed it for structural, electro-optical, and demonstrated the practical utility of HTL in PSCs in its pristine form. The designed fluorinated HTL called tri(3-fluoro-4-methoxy-N-(4-methoxyphenyl)aniline) triphenylamine (FOMePh), gave higher power conversion efficiency (PCE) of 17.08% which supersede with doped Spiro- OMeTAD (16.9%) while consuming 2.3 times lesser materials as of Spiro-OMeTAD for PSCs fabrication. We made the synthetic cost analysis and FOMePh was calculated to be 80.19 €/g which is four-time lower than the cost of Spiro-OMeTAD. To investigate the impact of fluorine atoms, we synthesize molecules without fluorine atoms (OMePh). The FOMePh and OMePh owned hole mobility of 5.9 × 10 -4 and 3.59 × 10 -5 cm 2 V -1 s -1 , which is on par with doped Spiro-OMeTAD. The photovoltaics parameters suggest the performance of OMePh is dropped due to poor film formation ability as compared to FOMePh, and this has a bearing on the performance and reliability of PSCs. 1. Introduction Perovskite solar cells (PSCs) have received remarkable attention owing to their outstanding power conversion efficiency (PCE) 1-6 which can save solar energy in the chemical bands by different ways such as water splitting with the production of Hydrogen gas (H2) and molecular oxygen (O2) as the clean by-product. 7, 8 PSCs are fabricated following mainly two different configurations which rely on whether the hole transport layer (HTL) or electron transport layer (ETL) is deposited on transparent conducting oxide (FTO) respectively. This former is called “inverted architecture” (positive-intrinsic-negative, p-i-n), while the one is termed as “standard architecture” (negative-intrinsic-positive, n-i-p). 9 The effect of HTLs on hole extraction and stability is fundamental. 10-12 However, in n-i-p based PSCs HTLs suffer from low electrical conductivity and hole mobility of p-type organic semiconductors, which is being addressed by the use of dopants. One of the most studied HTL is Spiro-OMeTAD in which the poor electrical properties and high cost limit its widespread application. 13, 14 Moreover, in the case of Spiro- OMeTAD, it shows absorbance near to 400 nm and competes with the perovskite light absorbance, which can decrease the PCE since in p-i-n based PSCs light passes from the HTL layer first. 15 Arguably, doping can increase the charge extraction to get collected at the contact surface of the HTL and perovskite which triggers high fill factors (FF) and open-circuit voltage (Voc). This doping is being employed in the case of Spiro- OMeTAD and many other HTLs such as PEDOT: PSS 16 , PTAA 17 , and P3HT 18 to increase the conductivity and hole mobility by using Li-based dopants such as LiTFSI and 4-tert-butyl pyridine (t-BP) as an additive. Nevertheless, Li-based dopant harms the stability of PSCs due to their high hygroscopic properties. 19, 20 To decrease this problem, Hua et al. investigated the influence of fluorine atoms on the hydrophobicity of Li-dopant. The result showed that higher fluorine atoms (from 2 to 10 atoms) improved charge-carrier transfer and photovoltaic performances in PSCs. 21 The design and validation of an innovative cost-effective, dopant-free HTL, 22, 23 with good electrical properties and high stability are paramount for scalability. 24 Fluorinated-based molecular semiconductors have high hydrophobicity, and rational molecular packing to trigger higher hole mobility and conductivity with compatible energy levels to perovskite as HTLs. 25 Recently, doped fluorinated Spiro-OMeTAD with PCE of 24.8% is reported. This PCE is correlated to lowering energy levels in fluorinated compared to pristine one and enhancing molecular packing in PSC. 6 To fabricate dopant-free PSCs, pyrene-based HTL was synthesized in multi-steps with triphenylamine substituents and device performance was investigated. The result showed fluorinated HTL has a better PCE compared with pristine HTL (5.9% vs 5.0%), and was ascribed to the quality of the film. 26 In a similar fashion central fluorinated phenyl core with pendant aryl amines-based PSCs achieved a stabilized PCE of 6% without the addition of ionic additives. 27 Hao et al. synthesized a new HTL with benzo di-thiophene core and di- fluorobenzene and 4,4′-di-methoxydiphenylamine as the branches called BDTOFMeDPA. The optimized PSCs with fluorinated HTL afford a decent PCE of 14.5%, while the non- a. BCMaterials, Basque Center for Materials, Applications and Nanostructures, Bld. Martina Casiano, UPV/EHU Science Park, Barrio Sarriena s/n, 48940 Leioa, Spain. b. IKERBASQUE, Basque Foundation for Science, Bilbao 48009, Spain. samrana.kazim@bcmaterials.net ; shahzada.ahmad@bcmaterials.net