Abstract
Many attempts have been made to stabilize α-phase formamidinium lead iodide (α-FAPbI3) using mixed cations or anions with MA+, FA+, Br− and I−. A representative method is to stably produce α-FAPbI3 by adding methylammonium lead (MAPbBr3) to the light absorption layer of a perovskite solar cell and using methylammonium chloride (MACl) as an additive. However, in the perovskite containing MA+ and Br−, the current density is lowered due to an unwanted increase in the bandgap; phase separation occurs due to the mixing of halides, and thermal stability is lowered. Therefore, in this study, in order to minimize the decrease in the composition ratio of FAPbI3 and to reduce MA+, the addition amount of MACl was first optimized. Thereafter, a new attempt was made to fabricate FAPbI3 perovskite by using formamidinium lead bromide (FAPbBr3) and MACl together as phase stabilizers instead of MAPbBr3. As for the FAPbI3-MAPbBr3 solar cell, the (FAPbI3)0.93(MAPbBr3)0.07 device showed the highest efficiency. On the other hand, in the case of the FAPbI3-FAPbBr3 solar cell, the (FAPbI3)0.99(FAPbBr3)0.01 solar cell with a very small FAPbBr3 composition ratio showed the highest efficiency with fast photovoltaic performance improvement and high crystallinity. In addition, the FAPbI3-FAPbBr3 solar cell showed a higher performance than the FAPbI3-MAPbBr3 solar cell, suggesting that FAPbBr3 can sufficiently replace MAPbBr3.
Highlights
Perovskite solar cells (PSCs) are still one of the most popular fields and within a short period of time since their advent, they have achieved high power conversion efficiencies (PCEs) exceeding 25% with broader solar-light absorption through narrower bandgaps
To determine the optimal composition ratio of MAPbBr3 and FAPbBr3, five devices were prepared under various methylammonium chloride (MACl) conditions (0–50 mol%, or 0–50-MACl)
As the MACl concentration increased to 50 mol%, the PCE decreased to 12.989%
Summary
Perovskite solar cells (PSCs) are still one of the most popular fields and within a short period of time since their advent, they have achieved high power conversion efficiencies (PCEs) exceeding 25% with broader solar-light absorption through narrower bandgaps. The first of two representative methods to overcome the phase transformation problem of α-FAPbI3 is the use of methylammonium chloride (MACl) as an additive in the perovskite precursor solution. FAPbI3-MAPbBr3 has been studied the most among all the processes for enhancing the phase stability of FAPbI3 and exhibited a higher PCE than the first method of adding MACl. In addition, MACl has been used together in the manufacture of FAPbI3-MAPbBr3 perovskite, and here MACl has been mainly used as ‘a mediator for high-crystallinity’. MACl has been used together in the manufacture of FAPbI3-MAPbBr3 perovskite, and here MACl has been mainly used as ‘a mediator for high-crystallinity’ This method has problems such as reduced light absorption, increased bandgap due to MAPbBr3, and reduced thermal stability owing to MA+ ions, resulting in a low current density [9]. To further improve the performance of PSCs, a novel configuration capable of stabilizing α-FAPbI3 without MA+ while controlling the bandgap increase inherent in FAPbI3 is required
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