Suppressing Ion Migration by Synergistic Engineering of Anion and Cation toward High-Performance Inverted Perovskite Solar Cells and Modules.

Ion migration-induced intrinsic instability and large-area fabrication pose a tough challenge for the commercial deployment of perovskite photovoltaics. Herein, an interface heterojunction and metal electrode stabilization strategy is developed by suppressing ion migration via managing lead-based imperfections. After screening a series of cations and nonhalide anions, the ideal organic salt molecule dimethylammonium trifluoroacetate (DMATFA) consisting of dimethylammonium (DMA+) cation and trifluoroacetate (TFA-) anion is selected to manipulate the surface of perovskite films. DMA+ enables the conversion of active excess and/or unreacted PbI2 into stable new phase DMAPbI3, inhibiting photodecomposition of PbI2 and ion migration. Meanwhile, TFA- can suppress iodide ion migration through passivating undercoordinated Pb2+ and/or iodide vacancies. DMA+ and TFA- synergistically stabilize the heterojunction interface and silver electrode. The DMATFA-treated inverted perovskite solar cells and modules achieve a maximum efficiency of 25.03% (certified 24.65%, 0.1 cm2) and 20.58% (63.74 cm2), respectively, which is the record efficiency ever reported for the devices based on vacuum flash evaporation technology. The DMATFA modification results in outstanding operational stability, as evidenced by maintaining 91% of its original efficiency after 1520 h of maximum power point continuous tracking.

Grain boundary defects passivation by bridging diammonium toward stable and efficient perovskite solar cells.

The grain boundary defects of polycrystalline perovskite could induce severe carrier recombination loss to restrict the photovoltaic and stability advancement of perovskite-based solar cells (PSCs). Inserting fixed molar ratio organic cations spacers into halide perovskite slabs to reduce the dimension of the crystal structure is still limited in finding a compromise of efficiency and stability for the widened bandgap and increasing barriers for carrier transport. Here, we select a direct additive bridging engineering to introduce a rationally designed organic amine salt 1,4-Benzene diammonium iodide (BDAI2) with ammonium group on both terminals of the benzene ring to passivate the grain boundary and interface defects of perovskite. Bridging diammonium could ameliorate the interface contact and achieve electrostatic interactions with negatively charged traps (such as uncoordinated I-, PbI3-, and methylammonium vacancies) to inhibit cation migration, reduce halogen ion vacancy, and then suppress trap-induced recombination in perovskite. As a result, the bridging diammonium could improve the power conversion efficiency (PCE) from 19.86% to 21.91%. This study highlights the importance of rational bridging diammonium for perovskite surface modification and passivation to boost photovoltaic performance and stability.

Managing Interfacial Defects and Carriers by Synergistic Modulation of Functional Groups and Spatial Conformation for High-Performance Perovskite Photovoltaics Based on Vacuum Flash Method.

Interfacial nonradiative recombination loss is a huge barrier to advance the photovoltaic performance. Here, one effective interfacial defect and carrier dynamics management strategy by synergistic modulation of functional groups and spatial conformation of ammonium salt molecules is proposed. The surface treatment with 3-ammonium propionic acid iodide (3-APAI) does not form 2D perovskite passivation layer while the propylammonium ions and 5-aminopentanoic acid hydroiodide post-treatment lead to the formation of 2D perovskite passivation layers. Due to appropriate alkyl chain length, theoretical and experimental results manifest that COOH and NH3 + groups in 3-APAI molecules can form coordination bonding with undercoordinated Pb2+ and ionic bonding and hydrogen bonding with octahedron PbI6 4- , respectively, which makes both groups be simultaneously firmly anchored on the surface of perovskite films. This will strengthen defect passivation effect and improve interfacial carrier transport and transfer. The synergistic effect of functional groups and spatial conformation confers 3-APAI better defect passivation effect than 2D perovskite layers. The 3-APAI-modified device based on vacuum flash technology achieves an alluring peak efficiency of 24.72% (certified 23.68%), which is among highly efficient devices fabricated without antisolvents. Furthermore, the encapsulated 3-APAI-modified device degrades by less than 4% after 1400 h of continuous one sun illumination.

Zwitterionic ionic liquid synergistically induces interfacial dipole formation and traps state passivation for high-performance perovskite solar cells.

Defects at the interface and grain boundaries of perovskite solar cells (PSCs) will result in severe non-radiative recombination and open-circuit voltage (Voc) loss. Herein, we reported a zwitterionic ionic liquid imidazolium tetrafluoroborate (IMBF4) to passivate the defects at tin dioxide (SnO2)/perovskite interface. The results showed that the electron-rich nitrogen atom contained IM+ could diffuse into the buried perovskite to exhibit a strong chemical passivation effect on the organic vacancy defect by interacting with uncoordinated Pb2+. The F- in BF4- has a strong coordination effect with Pb2+in perovskite and Sn2+ in SnO2 synchronously to fill the anion vacancy defect. Also, the BF4- anions could help to form an interface dipole layer to increase the charge transfer rate and reduce the work function. The IMBF4 modified device could achieve an efficiency enhancement from 20.18% to 23.05% by vacuum flash-assisted solution-processed, with the increased Voc from 1.09 V to 1.15 V. The unencapsulated IMBF4 modified device could maintain 93% of the initial efficiency after ageing for 2000 h under ambient conditions by the ISOS-D-1 stability-testing protocols. This work emphasizes the importance of multifunctional additives in passivating defects and improving interface contact for achieving efficient and stable perovskite solar cells.

Heterojunction In Situ Constructed by a Novel Amino Acid-Based Organic Spacer for Efficient and Stable Perovskite Solar Cells.

The optical properties and stability of metal halide perovskites can be improved by reducing their dimensionality. Because defects at the perovskite film grain body and boundaries cause significant energetic losses by nonradiative recombination, perovskite films with manageable crystal size and macroscopic grains are essential to improve the photovoltaic properties. Through theoretical calculation models and experiments, we show that the carboxyl group of 4-ammonium butyric acid-based cation (4-ABA+) can interact with the three-dimensional (3D) perovskite to produce in situ a secondary grain growth by post-treatment. It passivates the trap defects and broadens the light absorption. 4-ABA+ could induce a 2D capping layer on top of 3D mixed cation-based perovskite to construct a 2D/3D heterojunction. The 4-ABA+-modified perovskite film consists of large-sized grains with extremely low trap state densities and possesses a longer charge carrier lifetime and good stability, resulting in efficient perovskite solar cells with a champion efficiency of 23.16% and a VOC of 1.20 V. We show that the 4-ABA+-treated devices outperform the 3-ammonium propionic acid (3-APA+)- and 5-ammonium valeric acid (5-AVA+)-treated ones. Moreover, the devices exhibit high stability under high humidity and continuous light soaking conditions. This work gives a hint that our approach based on 4-ABA+ treatment is key to achieving better electrical properties, a controlled crystal growth, and highly stable perovskite solar cells.

Functionalizing phenethylammonium by methoxy to achieve low-dimensional interface defects passivation for efficient and stable perovskite solar cells.

Low dimensional interface passivation has been proved to be an efficient method to lessen the nonradiative recombination loss in perovskite solar cells. To overcome the limitation of Phenethylammonium (PEA+) for carrier transport and water molecule intrusion, we developed a modification strategy by functioning the typical PEA+with the 4-methoxy to optimize the interface defects and carrier transport performance, thus maximizing the synchronous improvement of device efficiency and stability. Our results indicate that the 2 mg ml-14-methoxy-phenethylammonium (MeO-PEA+) modified device could achieve a best power conversion efficiency of 19.64% with improved shelf-life stability in ambient conditions. The new passivation molecule of MeO-PEA+could possess the capability of defect passivation, carrier transfer, and moisture blocking, demonstrating that rationally designed organic components for interface passivation could help to achieve efficient and stable PSCs.