Materials engineering is key to improving the stability and photovoltaic parameters of inverted perovskite solar cells (PSCs). This work presents the effect of two different fluorinated additives on the performance of PSCs containing the archetypal three‐dimensional perovskite, methylammonium lead triiodide (MAPbI3). 3‐(2,3,4,5,6‐Pentafluorophenyl)propylammonium iodide (FPAI) is added to the anode modifying layer and (2,3,4,5,6‐pentafluorophenyl)methylammonium bromide (FMABr) is blended into the perovskite layer. The inverted devices containing FPAI in the anode modifying layer and 0.32 mol% of FMABr from the perovskite precursor solution had hysteresis‐free current density‐voltage characteristics and a maximum power conversion efficiency of 22.3%, which is an absolute increase of 1.7% compared to the MAPbI3 device (20.6%) of the same architecture but without the additives.

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An attempt has been made to synthesize (Ca 0.4 Sr 0. 6)Bi 4 Ti 4 O 15 (CSBT) thin film using pulsed laser deposition (PLD) and successfully optimized the deposition conditions. A good quality film with the desired phase is obtained at a substrate temperature of 650 o C based on phase, composition and morphology studies. Highly c-axis oriented films with average thickness 330-400 nm and an average grain size 40-65 nm has been found. Piezoresponse force microscopy (PFM) showed a complete domain reversal using switching spectroscopy. A comparatively high effective d 33 * value as ~120 pm/V has been achived. The results suggest that CSBT has a great potential in electromechanical applications. 2 1.Introduction Bismuth layer-structured ferroelectrics (BLSFs) have drawn much interest of the researchers due to their application in thin film memory devices, high-temperature electromechanical devices owing to their high Curie temperature (T C ), good ferroelectric properties, good fatigue resistance andafter all their lead-free nature [1]. Sensors, actuators, and transducers operating at elevated temperatures (~400 o C) are highly desired in industries such as energy, engines, oil and gas, and chemicals. In these applications, the operating temperature should not exceed half of the Curietemperature (T C ) of piezoelectric materials. Piezoelectric materials based on BLSFs are the potential candidate to operate at high-temperature and provide intended functionality. BLSFs belong to Aurivillius phase with the general chemical formula (Bi 2 O 2 ) 2+ (A m-1 B m O 3m+1 ) 2where A is one or more mono-, di-, or trivalent ions (Sr 2+ , Ba 2+ , Ca 2+ , Bi 3+ etc. or combination), B is tetra-, penta-or hexavalent ions (Ti 4+ , Ta 5+ , Nb 5+ , etc.) and m ( = 1, 2, 3, 4, etc.) is the number of the BO 6 octahedra regularly interleaved by (Bi 2 O 2 ) 2+ layer along c-axis[2]. The piezoelectric propertiesinthese BLSF compounds are greatly influenced by the number of layers and the elements present in the A and B site [1]. Thus, the properties of these compounds can be enhanced by incorporating different cations at site A or B or both [3]. However, it has been reported that the Curie temperature of BLSFs decreases when the size of the cations at A-site increases, while Curie temperature increases and the electrical properties are augmented significantly due to the replacement of A-site cation by a smaller size ion [4]. In addition, most of the BLSFs possess a relatively high electrical conductivity which makes the poling process difficult. Among the various BLSFs are studied, the compounds, MBi 4 Ti 4 O 15 with m = 4 and M = Sr, Ca, Ba have been investigated extensively due to their better ferroelectric properties [2, 4-