Vapor Deposited Pure α‐FAPbI₃ Perovskite Solar Cell via Moisture‐Induced Phase Transition Strategy

Abstract

To fabricate stable neat FAPbI3 perovskite with a pure α‐phase (pure α‐FAPbI3) is important in the field of photovoltaic commercialization because of its better bandgap than its alloying counterpart with cesium (Cs) or methylammonium (MA) cations. In this study, the first vapor deposited pure α‐FAPbI3 thin film solar cell with a power conversion efficiency (PCE) over 20% is achieved by regulating the phase transition process. It is found that under high humidity conditions, a fast phase transition between high‐purity α‐ and δ‐phase FAPbI3 can be realized. Moreover, theoretical calculations interestingly reveal a phase transition shortcut induced by the abnormal volume contraction that is ascribed to the formation of double hydrogen bonds at a certain H2O concentration. Therefore, a high‐humidity post‐treatment strategy is proposed to fabricate α‐FAPbI3 solar cells with a champion PCE of 20.19% (0.1 cm2) and 18.91% (1 cm2), which is currently the highest recorded value in vapor deposited pure α‐FAPbI3 perovskite solar cells. This study helps to redefine the effect of a water molecule on FAPbI3 solar cells. In addition, the demonstrated scaling‐up possibility provides another perspective for fabricating uniform high‐performance pure α‐FAPbI3 perovskite solar cells.

Photovoltaic Performance of FAPbI3 Perovskite Is Hampered by Intrinsic Quantum Confinement

“…At room temperature, the desired perovskite α-phase is only metastable and easily deteriorates into a thermodynamically favorable, yellow, nonperovskite 2H (δ)-phase that is not particularly photoactive . Early work demonstrated that partial substitution of FA with Cs with as little as 5% − is sufficient to eliminate traces of δ-phase presence in XRD patterns, , but such a degree of A-site alloying shifts the band gap to higher energies and has been shown to introduce undesirable compositional inhomogeneities. , Recently, a plethora of fabrication methods and optimization approaches have therefore been developed to attain and stabilize the “unalloyed” perovskite α-phase of FAPbI 3 . ,,,,− These alterations to earlier fabrication methods vary from introducing pre- and postannealing steps and additive treatments , to more elaborate stoichiometric engineering techniques, ,, vapor codeposition, and more recently templating and sequential deposition strategies via solution or vapor deposition routes, yielding significant advances in stability and performance.…”

Self‐Healing Perovskite Grain Boundaries in Efficient and Stable Solar Cells via Incorporation of 502 Adhesive

“…The decreased RMS value further confirms the enhanced quality of perovskite film with adding optimized amount of 502 adhesive. [ 33 ]…”

“…The decreased RMS value further confirms the enhanced quality of perovskite film with adding optimized amount of 502 adhesive. [33] To investigate the effect of 502 adhesive on photovoltaic performance, the PSCs with planar structure of FTO/SnO 2 / Perovskite/Spiro-OMeTAD/Ag were prepared (Figure 3a). We tuned the concentration of 502 adhesive in perovskite films to optimize the device performance.…”

Applications of vacuum vapor deposition for perovskite solar cells: A progress review

“…Secondly, it is difficult to monitor the evaporation rate of multiple precursors with a single QCM, making it unable to identify the individual evaporation rate of precursors, leaving a negative influence on reproducibility [26] . Lastly, it is reported that a small amount of the ammonium salt may remain in the chamber after evaporation, which may re-evaporate during the next evaporation process [30] . Such remnant precursors can affect the composition of the evaporated perovskite, reducing the batch-to-batch reproducibility of evaporated PSCs.…”