Simultaneous Enhanced Efficiency and Stability of Perovskite Solar Cells Using Adhesive Fluorinated Polymer Interfacial Material

Abstract

For enhancing the performance and long-term stability of perovskite solar cell (PSC) devices, interfacial engineering between the perovskite and hole-transporting material (HTM) is important. We developed a fluorinated conjugated polymer PFPT3 and used it as an interfacial layer between the perovskite and HTM layers in normal-type PSCs. Interaction of perovskite and PFPT3 via Pb–F bonding effectively induces an interfacial dipole moment, which resulted in energy-level bending; this was favorable for charge transfer and hole extraction at the interface. The PSC device achieved an increased efficiency of 22.00% with an open-circuit voltage of 1.13 V, short-circuit current density of 24.34 mA/cm2, and fill factor of 0.80 from a reverse scan and showed an averaged power conversion efficiency of 21.59%, which was averaged from forward and reverse scans. Furthermore, the device with PFPT3 showed much improved stability under an 85% RH condition because hydrophobic PFPT3 reduced water permeation into the perovskite layer, and more importantly, the enhanced contact adhesion at the PFPT3-mediated perovskite/HTM interface suppressed surface delamination and retarded water intrusion. The fluorinated conjugated polymeric interfacial material is effective for improving not only the efficiency but also the stability of the PSC devices.

Multifunctional π‐Conjugated Additives for Halide Perovskite

“…Lots of reported conjugated molecules for PSCs anchor to the perovskite film via incorporation with uncoordinated Pb 2+ by amino groups, [ 46 , 49 , 53 , 69 ] carbonyl groups, [ 27 , 43 , 51 , 68 ] cyano groups, [ 51 ] sulfur atoms, [ 58 , 67 ] or fluorine atoms. [ 28 , 29 ] In PeLEDs, poly[(9,9‐bis(3’‐( N , N ‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] (PFN), [ 73 ] PFN‐X (I, Br, Cl), [ 74 ] poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (PFO), [ 75 ] poly(9,9‐bis(4′‐sulfonatobutyl)fluorene‐alt‐1,4‐phenylene) potassium (FPS‐K) and poly(9,9‐bis(4′‐sulfonatobutyl)fluorene‐alt‐1,4‐phenylene)tetramethylammonium (FPS‐TMA), [ 76 ] poly(fluorene‐ co ‐phenylene)‐based anionic conjugated polyelectrolytes, [ 77 ] and 1,3,5‐ tris (bromomethyl) benzene (TBB) [ 78 ] are reported to dramatically improve the device performance by defect passivation. The interaction also exists between bare Pb 2+ and π ‐electrons.…”

“…In addition, π ‐conjugated molecules act as interfacial compatibilizer between perovskite and the HTMs are reported to improve the interface wettability and fabricate large and uniform perovskite films. [ 29 , 32 , 39 , 45 ] It is believed that amphiphilic π ‐conjugated molecule which has conjugated backbone and hydrophilic functional groups generally matches well with multiple types of CTLs.…”

“…when investigating the fluorinated conjugated polymer 5,5′‐(2,5‐difluoro‐1,4‐phenylene)bis(3‐[2‐decyltetradecyl]‐thiophene) and 3,3′‐difluoro‐2,2′‐bithiophene (PFPT3) as an interfacial layer between perovskite and HTL. [ 29 ] It is revealed that the electron density of the Pb in the perovskite structure decreased upon formation of the junction with PFPT3 and that the electron density of F in the polymer simultaneously increased because of electron transfer from the perovskite layer to PFPT3. As a result, the deposition of the perovskite using a low‐concentration PFPT3 (0.01 mg mL −1 ) led to a remarkable increase in the vacuum level (e.g., ϕ = 0.54 eV) (Figure 6d ).…”

Effects of polyethylene oxide particles on the photo-physical properties and stability of FA-rich perovskite solar cells

“…The ongoing research efforts are directed towards addressing this challenge while trying to increase the PCEs to higher levels 9 . Among the several approaches that have been explored, those that aim at engineering both the active layer (AL) and the interface with the charge transport layers (CTLs) have been cited as the most instrumental routes to achieve improvements in the PCEs, and the long-term stability of PSCs 10 – 13 . The improvements are attributed to the suppression of defects in the bulk of the perovskite film and the interfaces with the CTLs, which are usually difficult to avoid due to the solution-based processing of perovskite films 14 , 15 .…”

Optimal Solvents for Interfacial Solution Engineering of Perovskite Solar Cells

“…Solution processing is the preferred method for deposition because it is simpler and cheaper than other methods such as thermal evaporation, screen printing, and atomic layer deposition, [ 26–28 ] through which various interlayers have been deposited. [ 29 ] Dip‐coating [ 30,31 ] and spin‐coating methods [ 25,32–41 ] are extensively used in solution processing, with spin coating attracting greater attention because of its tendency to rapidly and conveniently fabricate monolayers. The selection of an appropriate organic solvent and interfacial materials is crucial in this solution processing method.…”