Structural and Photophysical Properties of Guanidinium–Iodide‐Treated Perovskite Solar Cells

Abstract

Use of the guanidinium iodide (GAI) cation is widely recognized as an interface engineering technique for perovskite solar cells that deliver stability improvements via defect passivation on surfaces and grain boundaries. However, a comprehensive understanding of the relationship between the structural and photophysical properties is lacking. Herein, GAI‐induced perovskite structural modifications, including derivative phases and underlying transitions, are detected in GAI surface‐treated Cs0.07MA0.14FA0.79Pb(I0.83Br0.17)3 through an analysis of X‐ray and electron diffraction and microscopy data. An optimum GAI solution concentration at 10 mg mL−1 can eliminate excess PbI2, improve crystallinity, and increase grain size of the as‐prepared perovskite films. However, a further increase to 20–40 mg mL−1 induces new (FAPbI3) x (GA2PbI4) x phases and a reduction in crystallinity and grain size. In addition, from confocal photoluminescence imaging, it is observed that 10 mg mL−1 GAI also helps to remove the microscale spatial heterogeneities, demonstrating optimum device performance. These results show that understanding the impact on structure and microstructure of the selection and concentration of surface treatment agents is critical for the homogenization of perovskite optoelectronic properties and achieving efficient device.

Single-Crystal Methylammonium-Free Perovskite Solar Cells with Efficiencies Exceeding 24% and High Thermal Stability

“…In Figure b, the PL peak distribution map of Cs 0.05 FA 0.95 PbI 3 SC remained relatively homogeneous after a week, unlike the case of the FA 0.6 MA 0.4 PbI 3 SC. The extensive inhomogeneity in the PL peak distribution map of the FA 0.6 MA 0.4 PbI 3 SCs is likely due to the formation of PbI 2 on the crystal surface from the degassing of MA after 8 days under damp heat conditions. ,, These observations demonstrate the outstanding crystalline quality retention and inhibition of surface defect generation in the Cs 0.05 FA 0.95 PbI 3 SC compared to the FA 0.6 MA 0.4 PbI 3 SC. Overall, both thermal and accelerated aging test results suggest that the Cs 0.05 FA 0.95 PbI 3 SC offers enhanced stability as an active material for SC-PSCs compared to the FA 0.6 MA 0.4 PbI 3 SC.…”

Alleviating nanostructural phase impurities enhances the optoelectronic properties, device performance and stability of cesium-formamidinium metal–halide perovskites

“…In this context, there is a lack of fundamental studies to characterize the local structure of CsFA perovskite absorbers compared to their triple-cations (CsMAFA) counterparts. [21][22][23][24] The reasons are manifold: generally, probing the perovskite nanostructure requires the use of transmission electron microscopy (TEM) techniques operating with high energy electrons (200 keV) where the beam-sensitive nature of hybrid perovskites makes it extremely challenging to obtain reliable local structural information from the pristine material. 25 Additionally, CsFA is challenging to fabricate in high crystal quality and compact morphology without optimized precursor solution ageing combined with the use of hydrohalic acids as additives; an experimental methodology that is incompatible to reproduce and imposes constraints on the process feasibility.…”

Machine Learning Enhanced High‐Throughput Fabrication and Optimization of Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells

“…The choice of GUA over other 2D cations confirms previous reports that found it to improve solar cell efficiency when used as a surface passivation material or integrated in the 3D-structure. [93][94][95][96] GUA is a comparably small spacer cation that allows for several hydrogen bonds and may be integrated into the 3D lattice to some extent. Consequently, GUA has been reported to improve the device efficiency of RPPs through its solvent effect, [78] incorporated into the octahedral sites of the perovskites [27] or as one of the binary spacer cations in RPPs where it improves the crystallization and orientation of the RP phases.…”