Improvement in the Performance of Inverted 3D/2D Perovskite Solar Cells by Ambient Exposure

Abstract

Perovskite solar cells (PSCs) are known to be sensitive to the exposure to ambient humidity, which typically results in the degradation and deterioration of performance, although positive effects of exposure to moisture have also been reported, due to recrystallization of the perovskite. Common approach to improve stability is to use 3D/2D perovskite active layer, where 2D capping layer is prepared by spin coating the bulky organic cation halide. Herein, it is shown that optimizing the exposure of the capping layer prepared by spin coating phenylethylammonium iodide (PEAI) to ambient atmosphere results in substantial improvement of the PSC performance. Furthermore, the initial effects of PEAI treatment are dependent on the NiO x /perovskite interface, but in all cases except at very high humidity (80–85% RH) optimized exposure to ambient results in improved performance. The variations in device performance with PEAI treatment and ambient exposure can be attributed to defect passivation and changes in the charge extraction due to energy‐level alignment at the interfaces. The best performing devices have passivation of NiO x /perovskite interface and PEAI treatment of top surface followed by exposure to ambient atmosphere at RH of 40–45%, which results in the power conversion efficiency increase from 20.3% to 22.4%.

Graded 2D/3D Perovskite Hetero-Structured Films with Suppressed Interfacial Recombination for Efficient and Stable Solar Cells via DABr Treatment

“…Figure 3 a shows the XRD patterns of 2D-3D based films with numerous DABr concentrations. As expected, MAPbI 3 -based film shows the prominent diffraction peaks of the pure phase tetragonal MAPbI 3 with moderate peak intensity [ 20 , 39 , 40 ]. For the DABr-treated films, the gradually strengthened pattern with the characteristic peak at ≈14.4° shows a little shift towards the higher degree planes.…”

“…Remarkably, the increased grain dimension of the perovskite film with DABr-2.5 could be caused by the newly formed layer that homogenously covered the control film, which is speculated to be the 2D perovskite capping layer. Therefore, the large grain 2D capping layer with fewer grain boundaries can suppress the defects of perovskite, resulting in inhibiting the non-radiative recombination and enhancing the device’s performance [ 38 , 39 , 40 ]. The SEM images confirmed that surface treatment with a suitable small amount of DABr can promote a homogenous film crystallization, leading to good quality 2D-3D-stacked films with large grains and homogeneous surface morphology.…”

“…For the DABr-treated films, the gradually strengthened pattern with the characteristic peak at ≈14.4° shows a little shift towards the higher degree planes. As shown in Figure 3 b, all three dominant peaks of the DABr-treated films are slightly shifted to larger diffraction angles, perhaps due to the incorporation of small radius Br ions into the base 3D MAPbI 3 layer [ 38 , 39 , 40 , 41 ]. As shown in Figure 3 a, the peaks under 10° are observed in the XRD patterns of DABr-treated perovskite films, which is the evidence for the appearance of 2D perovskite phase [ 35 , 39 , 40 ].…”

“…As shown in Figure 3 b, all three dominant peaks of the DABr-treated films are slightly shifted to larger diffraction angles, perhaps due to the incorporation of small radius Br ions into the base 3D MAPbI 3 layer [ 38 , 39 , 40 , 41 ]. As shown in Figure 3 a, the peaks under 10° are observed in the XRD patterns of DABr-treated perovskite films, which is the evidence for the appearance of 2D perovskite phase [ 35 , 39 , 40 ]. It is noticeable that the peak intensities of XRD pattern increase as the perovskite layer treats with DABr and the peak intensity rises up to the highest in DABr-2.5-treated perovskite film, which indicates the enhanced crystallinity of perovskite film, as shown in Figure 3 a [ 42 , 43 ].…”

“…The peaks of I 3d and Pb 4f shifted to larger energy binding as the perovskite treated DABr-2.5, demonstrating that there is an interaction between DABr, Pb 2+ , and I − [ 20 , 30 , 31 , 32 ]. Based on the above-mentioned analyses, we came forward with a credible proposed notion regarding the intermediary transitional process for the synthesis of high-quality MAPbI 3 -base film with larger grain size and less defect crystallinity [ 40 , 41 , 42 , 43 ].…”