Ammonium Sulfate to Modulate Crystallization for High-Performance Rigid and Flexible Perovskite Solar Cells.

Perovskite solar cells (PSCs) are attracting widespread research and attention as highly promising candidates in the field of electronic photovoltaics owing to their exceptional power conversion efficiency (PCE). However, rigid or flexible PSCs still face challenges in preparing full-coverage and low-defect perovskite films, as well as achieving highly reproducible and highly stable devices. Herein, a multifunctional additive 2-aminoethyl hydrogen sulfate (AES) is designed to regulate the film crystallization and thereby form flat and pinhole-free perovskite films. It is found that the introduction of AES can effectively passivate defects, restrain charge carrier recombination, and then achieve a higher fill factor. As seen with grazing incidence wide-angle X-ray scattering (GIWAXS), this approach does not affect the crystal orientation distribution. It is observed that AES addition shows a universality across different perovskite components since the PCE is improved up to 20.7% for FA0.97MA0.03Pb(I0.97Br0.03)3-AES, 22.85% for Cs0.05FA0.95PbI3-AES, 22.23% for FAPbI2.7Br0.3-AES, and 23.32% for FAPI-AES rigid devices. Remarkably, the non-encapsulated flexible Cs0.05 (FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 device with AES additive delivers a PCE of 20.1% and maintains over 97% of its initial efficiency under ambient conditions (25 ± 5% relative humidity) over 2280 h of aging.

Highly Stable Perovskite Solar Cells Based on the Efficient Interaction between Pb2+ and Cyano Groups of 4-Aminophthalonitrile.

Defects present on the top surface of perovskite films have a pronounced detrimental impact on the photovoltaic performance and stability of perovskite solar cells (PSCs). Consequently, the development of effective defect passivation strategies has become key in enhancing both the power conversion efficiency (PCE) and stability of PSCs. In this study, a small molecule material, 4-Aminophthalonitrile (4-APN), was introduced as a means to mitigate surface defects within perovskite films. Obviously, 4-APN effectively passivates the defects at grain boundaries by combining cyano groups (-C≡N) with Pb2+ , significantly reducing the density of defect states, inhibiting non-radiative recombination at the interface, and promoting the charge transfer efficiency from the perovskite layer to the hole transport layer. The 4-APN modification led to a significant upswing in the PCE, while concurrently bolstering the overall device stability. Importantly, the devices on 4-APN as passivation additive exhibited negligible performance degradation aging for 1200 h.

High-Fill-Factor Perovskite Solar Cells via Pseudohalide Salt Modification of the Substrate to Mitigate Nonradiative Recombination at the Interface.

The utilization of the sol-gel method for fabricating planar SnO2 as the electron transport layer (ETL) induces numerous defects on the SnO2 layer surface and perovskite film bottom, causing considerable deterioration of the device performance. Conventional inorganic salt-doped SnO2 precursor solutions used for passivation may cause incomplete substrate coverage due to the presence of inorganic salt crystals, further degrading the device performance. Here, a substrate modification approach involving the pretreatment of a fluorine-doped SnO2 (FTO) substrate with NH4PF6 is proposed. The interaction between PF6- ions and the FTO substrate enhances SnO2 film quality; excess PF6- ions decrease the number of defects on the film surface. NH4+ ions react with an -OH stabilizing agent in the SnO2 solution and are eliminated during annealing. The combined effects suppress nonradiative recombination and ion migration at the ETL-perovskite interface. The corresponding high-quality perovskite solar cells (PSCs) exhibit a fill factor of ∼0.825; PSC efficiency increases from 19.59% to 22.32%.

Enhancing the Efficiency of Perovskite Solar Cells by Bidirectional Modification of the Perovskite and Electron Transport Layer.

In perovskite solar cells (PSCs), the numerous defects present on the surface of the SnO2 electron transport layer (ETL) and the bottom of the perovskite film limit their power conversion efficiency (PCE) and stability. In view of this, a bidirectional modification strategy is designed using formamidine acetate (FAAc) to passivate the defects on the SnO2 ETL surface and bottom of the perovskite simultaneously. FA+ cations act on the harmful hydroxyl groups on the SnO2 ETL surface, whereas Ac- anions act on the iodine vacancy defect at the bottom of the perovskite. Because the interface defect is well passivated by FAAc, the interfacial charge recombination is restrained. This results in a significant increase in the filling factor of the PSC to ∼0.83 and the consequent increase in PCE to 23.05%, which considerably improves the stability. Bidirectional modification technology is an effective strategy for improving the PCE and stability of PSCs.