Polymer‐Assisted Heterogeneous Lead Iodide in a Two‐Step Process: Fabrication of Efficient and Stable Perovskite Solar Cells

Abstract

Developing pinhole‐free, superior crystal, and high‐quality perovskite films by regulating the lead iodide microstructure in two‐step sequential deposition has attracted increased interest in the domain of perovskite solar cells (PSCs) for commercial applications. Herein, a multifunctional polymer, polyvinyl alcohol (PVA), is incorporated into a two‐step sequential deposition process to regulate morphological transform of PbI2 and then the high‐quality perovskite films are obtained. PVA as a scaffold combines with uncoordinated Pb2+ in the PbI2 precursor solution through a strong Pb–O interaction, leading to rough PbI2. In the second step, the uneven and heterogeneous PbI2 allows FA&MA permeation and then drives adequate coordination reactions between PbI64− octahedron and bulky cations. Furthermore, the PVA gathering at grain boundary passivates redundant Pb2+ by the PbO bonding interactions in the final polycrystalline films. Consequently, high‐quality (FAPbI3)0.90(MAPbBr3)0.10 perovskite layers are obtained with promoted crystal growth, inhibited voids formation/delamination, and thus reduced trap states. The universality and versatility of this strategy not only enables improved power conversion efficiencies of 22.81% (Ag‐based devices) and 16.58% (carbon‐based devices) across architectures but also remarkedly enhances the device stability in ambient‐air aging condition, which delivers a facile and broadly applicable additive synergetic strategy for efficient and stable PSCs.

Enhancing performance of two‐step fabricated perovskite solar cells with sulfonium triflate‐based additive

“…This can be expected to help facilitate the diffusion of organic amine salt into the PbI 2 film, and induce a more efficient conversion to the perovskite. [20][21][22]32 Considering the effect of TPST on the PbI 2 structure, we anticipated that the crystal growth process of the perovskite structure would also undergo modifications. Figure 2A displays the XRD spectrum of the perovskite films.…”

“…[16][17][18][19] In addition, some researchers have investigated the use of polymers to generate an uneven surface on PbI 2 that results in a porous structure. 20 This creation of a lessordered or porous structure within the PbI 2 layer can facilitate the penetration of organic materials into the layers. Many attempts have explored that objective, with smallsize succinimide additives using nanoimprint techniques, 21 the selective formation of porous PbI 2 crystals with large clusters [22][23][24] and the removal of DMSO from the formed PbI 2 layer.…”

“…Notably, researchers have examined effectiveness of additive assisted two step method, such as CsI, HCl or even organic salts, to the PbI 2 precursor solution in order to disrupt the original PbI 2 structure and generate a less‐ordered (or amorphous) state 16–19 . In addition, some researchers have investigated the use of polymers to generate an uneven surface on PbI 2 that results in a porous structure 20 . This creation of a less‐ordered or porous structure within the PbI 2 layer can facilitate the penetration of organic materials into the layers.…”

Enhanced Perovskite Photovoltaics with Non-conjugated Polymers: Recent Developments and Future Prospects

“…Multifunctional polymer PVA can be introduced into the two-step orderly deposition process to control the morphological transformation of PbI 2 and form high-quality perovskite films. In the work by Li et al, PVA interacted with uncoordinated Pb 2+ in the PbI 2 precursor solution through a strong Pb-O interaction, resulting in the formation of PbI 2 . In the subsequent step, the uneven and heterogeneous PbI 2 allowed for the permeation of formamidinium (FA) and MA, facilitating the complete coordination reaction between PbI 6 4– octahedra and the large-volume cations.…”

Ionic liquid-regulated PbI2 layers and defect passivation for efficient perovskite solar cells

“…In particular, additive engineering is an effective way to modify the PbI 2 porosity and perovskite crystallization. 20,21 It was reported that hexamethylphosphoramide (HMPA) with high binding affinity and high boiling point was incorporated into the PbI 2 precursor to modify the morpgology and internal structure of the PbI 2 layer, which helped the infiltration of the second-step organic salt to form the perovskite thin film with uniform surface, large grains and reduced defects. 22 Chen and coworkers found that the modified PbI 2 thin film with 4-(aminomethyl) benzonitrile hydrochloride (AMBNCl) facilitated the fabrication of compact perovskite films with large grains and pinhole-free structures, 23 which leads to the passivation of defects of Pb 2+ , modulation of the energy level array and alleviation of nonradiative recombination.…”