Interfacial Dipole poly(2-ethyl-2-oxazoline) Modification Triggers Simultaneous Band Alignment and Passivation for Air-Stable Perovskite Solar Cells

Abstract

To promote the performance of perovskite solar cells (PSCs), its theoretical power conversion efficiency (PCE) and high stability, elaborative defect passivation, and interfacial engineering at the molecular level are required to regulate the optoelectric properties and charge transporting process at the perovskite/hole transport layer (HTL) interfaces. Herein, we introduce for the first time a multifunctional dipole polymer poly(2-ethyl-2-oxazoline) (PEOz) between the perovskite and Spiro-OMeTAD HTL in planar n-i-p PSCs, which advances the PSCs toward both high efficiency and excellent stability by stimulating three beneficial effects. First, the ether–oxygen unshared electron pairs in PEOz chemically react with unsaturated Pb2+ on the perovskite surfaces by forming a strong Pb–O bond, which effectively reduces the uncoordinated defects on the perovskite surfaces and enhances the absorption ability of the resulting PSCs. Second, the dipole induced by PEOz at the perovskite/HTL interface can decrease the HOMO and LUMO level of Spiro-OMeTAD and optimize the band alignment between these layers, thereby suppressing the interfacial recombination and accelerating the hole transport/extraction ability in the cell. Third, the hygroscopic PEOz thin film can protect perovskite film from water erosion by absorbing the water molecules before perovskite does. Finally, the PEOz-modified PSC exhibits an optimized PCE of 21.86%, with a high short-circuit current density (Jsc) of 24.88 mA/cm2, a fill factor (FF) of 0.79, and an open-circuit voltage (Voc) of 1.11 V. The unencapsulated devices also deliver excellent operation stability over 300 h in an ambient atmosphere with a humidity of 30~40% and more than 10 h under thermal stress.

Benzoic acid inhibits intrinsic ion migration for efficient and stable perovskite solar cells

“…[1][2][3] Nowadays, PSC has realized a power conversion efficiency (PCE) of 26.1%, comparable with those of the market silicon solar cells, which is mainly attributed to the low excitation energy, excellent light absorbency and long carrier lifetime of halide perovskite materials. [4][5][6][7][8][9] Although the PSC has made some progress in recent years, the defects of grain boundary, I vacancy (V I ) and Pb vacancy (V PB ) in hybrid perovskite lms are still striking. 1,3,10 The above defects and the grain boundaries can be named as trap states, trapping/recombining photogenerated carriers, [11][12][13][14] which severely affects the PSC efficiency and device stability.…”

Taurine as a powerful passivator of perovskite layer for efficient and stable perovskite solar cells

“…2 These great achievements can be attributed to the excellent light absorbing property, relatively low excitation energy, long carrier lifetime, and active carrier mobility of halide perovskite materials. 3–7…”

“…2 These great achievements can be attributed to the excellent light absorbing property, relatively low excitation energy, long carrier lifetime, and active carrier mobility of halide perovskite materials. [3][4][5][6][7] However, the ionic lattice characteristics and relatively low formation energy of halide perovskite materials give rise to various intrinsic defects, such as vacancies and low coordination Pb 2+ and I − ions, during lm formation and device operation. [8][9][10] These defects in the perovskite lattice can act as carrier nonradiative recombination sites and seriously lower the open-circuit voltage (V OC ) and ll factor (FF) of the devices.…”

Enhancing the Photovoltaic Performance of Perovskite Solar Cells by Doping 2-mercaptoimidazole in the Active Layer

“…8 Additive engineering is an important passivation method for reducing defects in perovskites, which can well improve the overall performance of PSCs. 9,10 Uncoordinated Pb 2+ generated by volatile organic components during thermal annealing is usually the main source of charge traps in perovskite films. 11 Lewis bases with hybrid atoms such as nitrogen, sulfur, oxygen, and phosphorus can coordinate with Pb 2+ through the contained lone pair electrons to neutralize their positive charges and reduce charge traps caused by vacancy defects.…”