A Two‐Stage Annealing Strategy for Crystallization Control of CH₃NH₃PbI₃ Films toward Highly Reproducible Perovskite Solar Cells

Abstract

The solvent-engineering method is widely used to fabricate top-performing perovskite solar cells, which, however, usually exhibit inferior reproducibility. Herein, a two-stage annealing (TSA) strategy is demonstrated for processing of perovskite films, namely, annealing the intermediate phase at 60 °C for the first stage then at 100 °C for the second stage. Compared to conventional direct annealing temperature (DHA) at 100 °C, using this strategy, MAPbI films become more controllable, leading to superior film uniformity and device reproducibility with the champion device efficiency reaching 19.8%. More specifically, the coefficient of variation of efficiency for 49 cells is reduced to 5.9%, compared to 9.8% for that using DHA. The TSA process is carefully studied using Fourier transform infrared spectroscopy, X-ray diffraction, and UV-vis absorption spectroscopy. It is found that in comparison with DHA the formation of hydrogen bonding and crystallization of perovskite are much slower and can be better controlled when using TSA. The improvements in film uniformity and device reproducibility are attributed to: 1) controllable MAPbI crystal growth stemming from the progressive formation of hydrogen bonding between methylammonium and halide; 2) suppression of intermediate phase film dewetting, which is believed to be due to its decreased mobility at the initial low-temperature annealing stage.

Influence of drying temperature on morphology of MAPbI3 thin films and the performance of solar cells

“…Based on Figure 1(a), we can see that there is an apparent increase of average MAPbI3 grain size with increasing the drying temperature we used from 60 o C to 70 o C. We suppose that this is due to the aggregation of small adjacent MAPbI3 grains just crystallized from intermediate product (MAI-DMSO-PbI2), which becomes more and more obvious with drying temperature above 60 o C in drying process. [18,24] Figure 1(b) shows that RMS roughness of MAPbI3 thin films rises abruptly with increasing drying temperature above 60 o C, in accordance with variation trend of grain size. In addition, we speculate that a faster evaporation of DMSO may slightly contribute to increase of surface roughness of MAPbI3 thin films.…”

Stable Perovskite Solar Cells Enabled by Simultaneous Surface and Bulk Defects Passivation

“…Meanwhile, the lower dark current of the passivated device suggests that the leakage paths related to charge loss are suppressed. [ 35 ]…”

Antisolvent-Derived Intermediate Phases for Low-Temperature Flexible Perovskite Solar Cells

“…43 In contrast, other antisolvents exchange more DMSO and DMF modules compared to TL, resulting from higher polarities, and as a result, FA + , MA + , and halogen anions are all inside crystals. Thus, other antisolvents derived the perovskite precursor in the supersaturation phase, which is in the form of (FA 0.85 MA 0.15 )X---PbX 2 ---(DMSO•DMF) with 1:1:1 stoichiometry, 44,45 where [Pb 3 X 8 ] octahedrons are supersaturated in the mixed solutions. Top-view SEM images of intermediate phases prepared by TL, CB, EA, and TCM and w/o treatment are given in Figure S6.…”