In Situ Formation of δ-FAPbI₃ at the Perovskite/Carbon Interface for Enhanced Photovoltage of Printable Mesoscopic Perovskite Solar Cells

Abstract

Formamidinium lead triiodide (FAPbI3) perovskite has attracted intensive research attention due to its ideal band gap and low defect density for photovoltaic applications. Particularly, the existence of non-photoactive δ-phase FAPbI3 has been considered detrimental to regular-structured perovskite solar cells (PSCs). Here, in hole-conductor-free triple-mesoscopic PSCs, we observe that α-phase FAPbI3 transforms to δ-phase FAPbI3 at the perovskite/carbon interface and in situ forms an α/δ-phase junction when the as-fabricated cells are exposed to humid atmosphere. The α/δ-phase junction shows a favorable band alignment and significantly suppresses the charge recombination at the interface. By controlling the relative humidity of the atmosphere, we fabricate FAPbI3-based cells that deliver a champion efficiency of 17.11% with an enhanced open-circuit voltage (V OC) of 1020 mV. This work demonstrates the potential of δ-phase FAPbI3 for benefiting the device performance of PSCs and proposes the concept of constructing perovskite-based junctions at the interface between a perovskite-absorbing layer and charge-transporting layers for enhancing the V OC of PSCs.

Carbon Electrode Endows High‐Efficiency Perovskite Photovoltaics Affordable, Fully Printable, and Durable

“…Through the rational design of perovskite compositions and perovskite-additive interaction, the PCEs based on TiO 2 /ZrO 2 /C mesoporous PSCs improved from 12.84% to 17.68%. [28][29][30][31][32] Unfortunately, one needs to carefully control the infiltration process of perovskite ink, in which the crystallization of perovskite crystals and the contact between perovskites and other active layers should be carefully optimized.…”

Ways to Improve the Performance of Triple‐Mesoscopic Hole‐Conductor‐Free Perovskite‐Based Solar Cells

“…One of the known passivation agents is different perovskite structures that have similar lattice mismatch and similar properties. Xiayan Chen, et al [ 51 ] introduced the passivation of α‐FAPbI 3 active phase by the δ‐FAPbI 3 yellow phase in MCPSCs. The FAPbI 3 ‐based devices were formed with the addition of 40% MACl to the perovskite solution.…”

“…Figure 5. a) Energy level diagram of α-FAPbI 3 and δ-FAPbI 3 , b) the molecular volume of both phases, and c) the parameters (open-circuit voltage [V OC ] and power conversion efficiency [PCE]) of the cell according to the time under humid conditions. Reproduced with permission [51]. Copyright 2022, American Chemical Society.…”

High-quality perovskite films prepared by nucleus epitaxial growth for efficient and stable perovskite solar cells

“…However, it was found recently that the concomitant existence of δ-FAPbI 3 can stabilize the α-phase structure and has no side effect on its absorption edge. 33,34…”