Abstract
Formamidinium (FA) lead halide (α‐FAPbI3) perovskites are promising materials for photovoltaic applications because of their excellent light harvesting capability (absorption edge 840 nm) and long carrier diffusion length. However, it is extremely difficult to prepare a pure α‐FAPbI3 phase because of its easy transformation into a nondesirable δ‐FAPbI3 phase. In the present study, a “perovskite” template (MAPbI3‐FAI‐PbI2‐DMSO) structure is used to avoid and suppress the formation of δ‐FAPbI3 phases. The perovskite structure is formed via postdeposition involving the treatment of colloidal MAI‐PbI2‐DMSO film with FAI before annealing. In situ X‐ray diffraction in vacuum shows no detectable δ‐FAPbI3 phase during the whole synthesis process when the sample is annealed from 100 to 180 °C. This method is found to reduce defects at grain boundaries and enhance the film quality as determined by means of photoluminescence mapping and Kelvin probe force microscopy. The perovskite solar cells (PSCs) fabricated by this method demonstrate a much‐enhanced short‐circuit current density ( J sc) of 24.99 mA cm−2 and a power conversion efficiency (PCE) of 21.24%, which is the highest efficiency reported for pure FAPbI3, with great stability under 800 h of thermal ageing and 500 h of light soaking in nitrogen.
Highlights
diffusion lengths.[2,3,4,5] it materials for photovoltaic applications because of their excellent light haris extremely difficult to obtain phase-pure vesting capability and long carrier diffusion length
The perovskite solar cells (PSCs) fabricated by this method demonstrate a much-enhanced short-circuit current density ( Jsc) of 24.99 mA cm−2 and a power conversion efficiency (PCE) of 21.24%, which is the highest efficiency reported for pure FAPbI3, with great stability under 800 h of thermal byproduct (δ-FAPbI3) during crystallization, which restricts the formation of pure cubic α-FAPbI3 perovskite.[3,10,11,12,13,14]
When the sample was annealed at the initial temperature of 100 °C, the color transformed into dark brown, and the final film turned completely black after the second stage of annealing, which occurred at 140 °C for an hour
Summary
Template-Assisted Formation of High-Quality α-Phase HC(NH2)2PbI3 Perovskite Solar Cells. In situ X-ray diffraction in vacuum shows no detectable δ-FAPbI3 phase during the whole synthesis process when the sample is annealed from 100 to 180 °C This method is found to reduce defects at grain boundaries and enhance the film quality as cation is difficult and that this perovskite structure is less stable than perovskite structures with the MA+ cation.[4,9] In addition, FAPbI3 is readily crystallized or transformed into an undesired nonperovskite determined by means of photoluminescence mapping and Kelvin probe force microscopy. The formation of δ-FAPbI3 and the transformation of α-MAPbI3 to α-FAPbI3 were verified by variable temperature X-ray diffraction (XRD), as there was no δ-FAPbI3 fingerprint peak during the annealing process from 100 up to 180 °C This method involved dripping a certain amount of FAI/IPA solution on the top of colloid-like MAI-PbI2-DMSO films, and a template-assisted perovskite structure was formed during annealing at 100 °C. The FAPbI3based PSC achieved a PCE of 21.24% with high stability under 800 h of thermal ageing and 500 h of light soaking with encapsulation
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