Efficient and Moisture-Stable Inverted Perovskite Solar Cells via n-Type Small-Molecule-Assisted Surface Treatment

Enhancing the Stability and Efficiency of Tin-Based Perovskite Solar Cells via Bifunctional Additive-Engineered Defect Passivation

Tin-based perovskites have been recognized as an optimal alternative to lead-based perovskites in the photovoltaic field due to their nontoxic nature and excellent optoelectrical properties. However, the efficiency and stability of tin-based perovskite solar cells (Sn-PSCs) as competing requirements are significantly worse than those of their lead-based counterparts, primarily due to the poor perovskite layer quality, Sn2+ oxidation, and high defect density. Herein, cyanamide (CA) with -C≡N and -NH2 groups is introduced as a multifunctional additive to the precursor solution of Sn-PSCs to improve crystallinity and suppress microstructure defects. A series of characterizations demonstrates that the CA molecules have strong interactions with Sn2+ and I-, thereby suppressing Sn2+ oxidation and migration of I-. The CA additives result in reduced defect density and inhibit carrier recombination. Consequently, the Sn-PSCs modified by CA additives (CA-modified PSC) achieve a champion PCE of 11.74%, which is much higher than 7.32% of the control devices. Significantly, the exposure of unencapsulated CA-modified PSC to a N2 atmosphere for 5000 h does not affect their initial efficiency, while the control devices show only 63% of their original efficiency. This work provides a straightforward and effective strategy for the development of efficient and stable Sn-PSCs.

P-Dopant with Spherical Anion for Stable n-i-p Perovskite Solar Cells

Li-TFSI/t-BP is the most widely utilized p-dopant for hole-transporting materials (HTMs) in state-of-the-art perovskite solar cells (PSCs). However, its nonuniformity of doping, along with the hygroscopicity and migration of dopants, results in the devices exhibiting limited stability and performance. This study reports on the utilization of a spherical anion derived from the p-dopant, regulated by its radius and shape, as an alternative to the linear TFSI- anion. The theoretical and experimental results reveal that the spherical anion significantly increases the doping effect of HTMs due to an enhanced electron transfer from larger dipole moments. The enhanced transfer leads to a shift in the Pb-6p defect orbitals, resulting in shallower trap states. Moreover, compared to the linear structure of the TFSI- anion, the anion of sodium tetrakis[3,5-bis(trifluoro methyl)phenyl]borate (Na-TFPB) with a larger van der Waals radius and spherical shape offers increased hydrophobicity and migration barriers, which can protect the perovskite crystal and facilitate stable p-doping of HTMs. The use of Na-TFPB results in enhanced thermal and ambient stability of PSCs. The devices fabricated with the shape- and radius-regulated p-dopant achieve remarkable efficiencies of 24.49 % and 24.31 % for CJ-01 and spiro-OMeTAD, respectively, representing the highest efficiency values for organic dopants to date. This study underscores the ingenious design of spherical anions of p-dopants in contrast to the conventional linear anions.

Supramolecular force-driven non-fullerene acceptors as an electron-transporting layer for efficient inverted perovskite solar cells

Fullerene derivatives are widely employed as efficient electron-transporting layers (ETLs) in p-i-n perovskite photovoltaics but face challenges in mitigating interfacial recombination losses and ensuring stable film morphology. Non-fullerene acceptors (NFAs), commonly utilized in organic photovoltaics, present a promising alternative to fullerene-based ETLs. Nevertheless, the suboptimal performance of NFA-based devices underscores the need for molecular engineering to tailor their properties. Herein, we develop two Y-type NFAs, Y-Phen and Y-CE, by substituting the benzothiadiazole core of Y6 with higher-polarity phenanthroline and crown ether. These modifications effectively enhance carrier kinetics by (1) promoting ordered molecular assembly on the perovskite surface through supramolecular interactions, thereby optimizing interfacial energetic alignment, and (2) improving the molecular packing to facilitate efficient charge transport. Using Y-CE as the ETL, the device achieves a certified power conversion efficiency (PCE) of 25.59%. Furthermore, the optimized device exhibits less than 10% degradation in PCE after 1440 hours of thermal aging. This work offers valuable insights into designing NFA-based ETLs for high-performance perovskite photovoltaics.

Enhancing the Efficiency and Stability of Inverted Perovskite Solar Cells and Modules through Top Interface Modification with N-type Semiconductors

The interface modification between perovskite and electron transport layer (ETL) plays a crucial role in achieving high performance inverted perovskite photovoltaics (i-PPVs). Herein, non-fullerene acceptors (NFAs), known as Y6-BO and Y7-BO, were utilized to modify the perovskite/ETL interface in i-PPVs. Non-polar solvent-soluble NFAs can effectively passivate surface defects without structural damage of the underlying perovskite films. Additionally, the improved phenyl-C61-butyric acid methyl ester (PCBM) ETL induced by NFAs modification significantly accelerates the electrons extraction. As a result, both Y6-BO and Y7-BO exhibit more effective interface modification effects compared to traditional PI molecules. The power conversion efficiency (PCE) of the inverted perovskite solar cell (i-PSC) modified with Y7-BO reaches 25.82 %. Moreover, the adoption of non-polar solvents and the superior semiconductor properties of Y7-BO molecules also enable perovskite solar modules (i-PSM) with effective areas of 50 cm2, 400 cm2, and 1160 cm2 to achieve record efficiencies of 23.05 %, 22.32 %, and 21.1 % (certified PCE), respectively, making them the best PCE reported in the literature. Importantly, enhanced interface mechanical strength between the perovskite and PCBM layer results in significantly improved environmental and operational stability of the cells. The cells modified with Y7-BO maintained 94.4 % of the initial efficiency after 1522 hours of maximum power point aging.

A Diphosphonic Acid-Based Interlayer for Highly Efficient and Stable Inverted Perovskite Solar Cells

We investigate an interlayer of 6,6'-bis(4-(bis(4-methoxyphenyl)amino)phenyl)-[1,1'-binaphthalene]-(2,2'-diyl)bis(oxy)bis(propane-3,1-diyl)bis(phosphonic acid) (BINOL-PA) with undoped poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) coverage. The incorporation of the 1,10-bi-2-naphthol central core enhances π-π stacking and reduces charge recombination at the interface. Compared to PTAA alone (0.95 eV), BINOL-PA/PTAA exhibits a shorter distance from the Fermi energy (EF) to the valence-band maximum (VBM) (0.36 eV). Two phosphoric acid units in BINOL-PA fine-tune the molecular dipoles. Theoretical calculations reveal electrostatic surface potential differences between BINOL-PA and PTAA in their backbone structure. Open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) results suggest suppressed interface recombination. The photovoltaic conversion efficiency (PCE), short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) for the BINOL-PA/PTAA device are measured as 21.02%, 22.67 mA cm-2, 1.12 V, and 82.8%, respectively, all higher than those achieved by the PTAA device with a PCE of 18%. BINOL-PA/PTAA significantly elevates VOC and FF values compared with dopant-free PTAA alone. The champion device retains over 89% of its initial PCE after being exposed to an ambient environment without encapsulation for more than 30 days. The thermal aging test conducted under a nitrogen atmosphere demonstrates that the efficiency retention rate for BINOL-PA/PTAA displays 60% of its initial efficiency after 1500 h.

Nitrogen-rich carbon dots as the antisolvent additive for perovskite-based photovoltaic devices

Solution-processed perovskite solar cells (PSCs) have demonstrated a tremendous growth in power conversion efficiency (PCE). A high-quality, defect-free perovskite-based active layer is a key point to enhance PSC performance. Introduction of additives and interlayers have proved to be an effective tool to passivate surface defects, control crystal growth, and improve PSC stability. Antisolvent engineering has emerged recently as a new approach, which aims to adjust perovskite layer properties and enhance the PCE and stability of PSC devices. Here, we demonstrate that carbon dots (CDs) may serve as a prospective additive for antisolvent engineering. Nitrogen-rich amphiphilic CDs were synthesized from amines by a solvothermal method and used as an additive to chlorobenzene for a perovskite layer fabrication. The interaction between perovskite and functional groups in CDs promotes improved crystallization of an active perovskite layer and defects passivation, bringing higher PSCs efficiency, stability, and suppressed hysteresis. Under optimized CD concentration, the maximum PCE increased by 34% due to the improved short-circuit current and fill factor, and the device maintains 87% of its initial efficiency after 6 d of storage under ambient conditions.

Non-Fullerene Acceptors Assisted Target Therapy for Interface Treatment Enable High Performance Inverted Perovskite Solar Cells

Targeted treatment of the interface between electron transport layers (ETL) and perovskite layers is highly desirable for achieving passivating effects and suppressing carrier nonradiative recombination, leading to high performance and long-term stability in perovskite solar cells (PSCs). In this study, a series of non-fullerene acceptors (NFAs, Y-H, Y-F, and Y-Cl) are introduced to optimize the properties of the perovskite/ETL interface. This optimization involves passivating Pb2+ defects, releasing stress, and modulating carrier dynamics through interactions with the perovskite. Remarkably, after modifying with NFAs, the absorption range of perovskite films into the near-infrared region is extended. As expected, Y-F, with the largest electrostatic potential, facilitates the strongest interaction between the perovskite and its functional groups. Consequently, champion power conversion efficiencies of 21.17%, 22.21%, 23.25%, and 22.31% are achieved for control, Y-H-, Y-F-, and Y-Cl-based FA0.88Cs0.12PbI2.64Br0.36 (FACs) devices, respectively. This treatment also enhances the heat stability and air stability of the corresponding devices. Additionally, these modifier layers are applied to enhance the efficiency of Cs0.05(FA0.95MA0.05)0.95PbI2.64Br0.36 (FAMA) devices. Notably, a champion PCE exceeding 24% is achieved in the Y-F-based FAMA device. Therefore, this study provides a facile and effective approach to target the interface, thereby improving the efficiency and stability of PSCs.

Anchoring Charge Selective Self-Assembled Monolayers for Tin-Lead Perovskite Solar Cells

Self-assembled monolayers (SAMs) have displayed great potential for improving efficiency and stability in p-i-n perovskite solar cells (PSCs). The anchoring of SAMs at the conductiv metal oxide substrates and their interaction with perovskite materials must be rationally tailored to ensure efficient charge carrier extraction and improved quality of the perovskite films. Herein, SAMs molecules with different anchoring groups and spacers to control the interaction with perovskite in the p-i-n mixed Sn-Pb PSCs are selected. It is found that the monolayer with the carboxylate group exhibits appropriate interaction and has a more favorable orientation and arrangement than that of the phosphate group. This results in reduced nonradiative recombination and enhanced crystallinity. In addition, the short chain length leads to an improved energy level alignment of SAMs with perovskite, improving hole extraction. As a result, the narrow bandgap (≈1.25 eV) Sn-Pb PSCs show efficiencies of up to 23.1% with an open-circuit voltage of up to 0.89 V. Unencapsulated devices retain 93% of their initial efficiency after storage in N2 atmosphere for over 2500 h. Overall, this work highlights the underexplored potential of SAMs for perovskite photovoltaics and provides essential findings on the influence of their structural modification.

Key Roles of Interfaces in Inverted Metal-Halide Perovskite Solar Cells

Metal-halide perovskite solar cells (PSCs), an emerging technology for transforming solar energy into a clean source of electricity, have reached efficiency levels comparable to those of commercial silicon cells. Compared with other types of PSCs, inverted perovskite solar cells (IPSCs) have shown promise with regard to commercialization due to their facile fabrication and excellent optoelectronic properties. The interlayer interfaces play an important role in the performance of perovskite cells, not only affecting charge transfer and transport, but also acting as a barrier against oxygen and moisture permeation. Herein, we describe and summarize the last three years of studies that summarize the advantages of interface engineering-based advances for the commercialization of IPSCs. This review includes a brief introduction of the structure and working principle of IPSCs, and analyzes how interfaces affect the performance of IPSC devices from the perspective of photovoltaic performance and device lifetime. In addition, a comprehensive summary of various interface engineering approaches to solving these problems and challenges in IPSCs, including the use of interlayers, interface modification, defect passivation, and others, is summarized. Moreover, based upon current developments and breakthroughs, fundamental and engineering perspectives on future commercialization pathways are provided for the innovation and design of next-generation IPSCs.

In situ dipole formation to achieve high open-circuit voltage in inverted perovskite solar cells via fluorinated pseudohalide engineering

Many studies have shown that the severe photoluminescence quantum yield (PLQY) loss at the interface between the perovskite and electron transport layer (ETL) is the main cause of voltage loss in inverted perovskite solar cells (p-i-n PSCs). However, currently there are no effective in situ passivation techniques to minimize this nonradiative recombination. Here, the fluorinated pseudohalide ionic liquid (FPH-IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) is introduced into the perovskite precursor formulation. EMIMTFSI can change the dielectric environment and energy-level arrangement of the perovskite by accumulating on the top surface and spontaneously forming dipoles. As a result, the excitonic binding energy (Eb) and nonradiative recombination loss are significantly reduced. At the same time, TFSI- reduces the formation energy of vacancy defects and stabilizes the perovskite phase by forming N-H⋯F hydrogen bonds between FA+ and the C-F bond in EMIMTFSI. Finally, the EMIMTFSI-modified p-i-n PSCs achieve an excellent efficiency of 24.81% with an impressive open-circuit voltage of 1.191 V for a 1.57 eV low-bandgap perovskite. In addition, the modified devices can maintain more than 95% PCE after continuous thermal aging at 85 °C for 500 h or illumination at the maximum power point for 800 h. This work provides a new idea for minimizing the non-radiative recombination losses in p-i-n PSCs.

Combining dithieno[3,2-f:2',3'-h]quinoxaline-based terpolymer and ternary strategies enabling high-efficiency organic solar cells

By incorporating a dithieno[3,2-f:2',3'-h]quinoxaline unit into a PM6 polymer backbone, we developed a novel terpolymer family, demonstrating composition-dependent optical, electrochemical, and morphological characteristics. Organic solar cells based on the combination of a terpolymer and ternary strategy achieved a high power conversion efficiency of 17.60%, demonstrating the validity of our combination strategy.