Roles of MACl in Sequentially Deposited Bromine‐Free Perovskite Absorbers for Efficient Solar Cells

Abstract

So far, the combination of methylammonium bromide/methylammonium chloride (MABr/MACl) or methylammonium iodide (MAI)/MACl is the most frequently used additives to stabilize formamidinium lead iodide (FAPbI3) fabricated by the sequential deposition method. However, the enlarged bandgap due to the addition of bromide and the ambiguous functions of these additives in lead iodide (PbI2) transformation are still worth considering. Herein, the roles of MACl in sequentially deposited Br‐free FA‐based perovskites are systematically investigated. It is found that MACl can finely regulate the PbI2/FAI reaction, tune the phase transition at room temperature, and adjust intermediate‐related perovskite crystallization and decomposition during thermal annealing. Compared to FAPbI3, the perovskite with MACl exhibits larger grain, longer carrier lifetime, and reduced trap density. The resultant solar cell therefore achieves a champion power conversion efficiency (PCE) of 23.1% under reverse scan with a stabilized power output of 23.0%. In addition, it shows much improved photostability under 100 mW cm−2 white illumination (xenon lamp) in nitrogen atmosphere without encapsulation.

Bifunctional SnO2 Colloid Offers No Annealing Effect Compact Layer and Mesoporous Scaffold for Efficient Perovskite Solar Cells

“…In this study, MACl modified FAPbI 3 was used as light absorber due to its larger grain, longer carrier lifetime, and reduced trap density than pristine FAPbI 3 described in our recent work. [ 40 ] We observed that the different SnO 2 layers show no significant influence on the morphology of the perovskite films (Figure S3, Supporting Information), which is also supported by contact angle images of SnO 2 layers with different processing temperatures (Figure S4, Supporting Information). Figure 3b shows the backward scan J–V curves of 200‐, 300‐, 400‐, and 500‐c‐SnO 2 planar devices with their best efficiencies, respectively.…”

Propylammonium Chloride Additive for Efficient and Stable FAPbI3 Perovskite Solar Cells

“…The residual chemical species left in the perovskite are crucial for the efficiency and stability of the PSCs. [20,49] MACl or PACl additive still exists in the perovskite film even after thermal annealing, which is proved by the 1 H NMR in Figure 5d. The protons in FA yield the apparent signal at ≈9.01, ≈8.65, and ≈7.85 ppm, whereas the 1 H NMR resonances locate at ≈2.38 ppm corresponding to CH 3 in MA.…”

Methodologies for >30% Efficient Perovskite Solar Cells via Enhancement of Voltage and Fill Factor

“…Among the studied additives, MACl has been widely demonstrated to be very effective in regulating perovskite crystallization kinetics and is usually employed to fabricate high-quality FAPbI 3based films in efficient PSCs. [2,30,31,50,54] Although MACl is very successful in preparing high-quality perovskite films, the mechanism of modulating crystallization kinetics has not been understood well. A systematic investigation was carried out to understand the role of MACl additive in modulating the crystallization of FAPbI 3 perovskite.…”

“…[16] J SC can maintain over 26 mA cm À2 when the replacement ratio of other cations for FA þ is less than 5%. [1,16,30] It is found obviously from Table 1 that J SC s are reduced from over 26 to 24-26 mA cm À2 when the substitution ratio is larger than 5% [32,[45][46][47][48][49][50] mainly due to the enlarged bandgaps. To further stabilize the black phase and improve film quality, Br À was incorporated to the FA-based mixed-cation perovskites to form (FAPbI 3 ) 1Àx (MAPbBr 3 ) x .…”

“…Additive engineering is an important approach for passivating defects, suppressing ion migration at grain boundaries (GBs) and protecting perovskite from moisture and oxygen gas via kinetic control of crystallization. Various additives have been proposed, such as Lewis acids, [94] Lewis bases, [22,25] low-dimensional perovskites, [95] ionic liquids, [96,97] ammonium salts, [1,50] etc. Among the studied additives, MACl has been widely demonstrated to be very effective in regulating perovskite crystallization kinetics and is usually employed to fabricate high-quality FAPbI 3based films in efficient PSCs.…”