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Deposition of a passivation layer on top of the perovskite is proven to be an effective method for improving the efficiency and long‐term stability of perovskite solar cells (PSCs). And the spin‐coating method is the most typical and popular method developed for this purpose. However, the spin‐coating method wastes substantial passivator materials, thus the quantitative relationship between the passivator amount and the device performance cannot be obtained. Herein, a quantitative deposition method is developed through drop‐on‐demand inkjet printing to investigate the influence of 2‐adamantylamine hydrochloride (2‐ADAHCl) deposition surface density on the device performance, which is found to have a significant impact on the device performance. A low deposition surface density of 1.1 µg cm−2 does not reach its optimum passivation capability. In contrast, an excess deposition surface density of 10.1 µg cm−2 would lead to energy level mismatch and large series resistance at the perovskite/hole transport layer (HTL) interface, thus resulting in inferior device properties. At an optimum deposition surface density of 2.5 µg cm−2, perovskite surface defects are greatly suppressed, and the interfacial contact between perovskite and HTL is improved. Finally, PSCs with a high efficiency of 24.57% are achieved with improved operational and environmental stabilities. [ABSTRACT FROM AUTHOR]

Perovskite films prepared by the solution process usually result in irregular grain orientation and rich buried interface defects, hindering the further improvement of device performance. Herein, multi‐fluorine‐containing C60‐ and C70 (higher fullerene)‐porphyrin derivatives, F60PD and F70PD, are synthesized and pre‐buried to modify the SnO2/perovskite heterointerface. The F70PD modification layer provides a better perovskite quality and more effective electron transporting capability compared to the corresponding F60PD, with the F70PD being more effective in regulating the perovskite growth, passivating the buried interface defects, and optimizing the interface energy level alignment. Consequently, the F70PD‐based device delivers superior efficiency and stability than the control and F60PD‐based devices. The F70PD‐based device yields a champion efficiency of 24.09% with negligible hysteresis. Meanwhile, due to the increased activation energy of ion migration, the F70PD‐based device maintains 80% of its initial efficiency after operating at the maximum power point for 1620 h. This study highlights the potential of designing higher fullerene materials for buried interface to further improve the perovskite solar cells' performance. [ABSTRACT FROM AUTHOR]

The non‐radiative recombination at the interfaces of perovskite solar cells (PSCs) is a crucial issue that limits the efficiency and stability of the devices. State‐of‐the‐art surface passivation strategies usually utilize alkyl ammonium halides to suppress the non‐radiative recombination of PSCs, but their high surface reactivity leads to the transformation into 2D perovskites under working conditions, limiting the passivation effect and the charge transport of PSCs. Herein, a non‐halide ionic salt 1‐naphthylmethylammonium formate (NMACOOH) is synthesized for surface passivation of perovskite films. In contrast to the traditional 1‐naphthylmethylammonium iodide, NMACOOH treatment hinders the formation of 2D perovskite and forms a thermally stable PbI2‐NMACOOH adduct on the perovskite surface. Surface characterization reveals that NMA+ can passivate the cation vacancies of the 3D perovskite while HCOO− passivates the metallic Pb0 and halide‐vacancy defects. Therefore, the non‐radiative recombination of PSCs is dramatically suppressed and a high open‐circuit voltage of 1.19 V is obtained. Finally, PSCs with high efficiency of 24.75% and improved long‐term stability (98% of the initial efficiency after 1800‐h storage) are obtained. Moreover, the NMACOOH‐passivated devices also show robust operational stability, retaining 83% of the initial efficiency after working for 658 h under continuous one‐sun illumination. [ABSTRACT FROM AUTHOR]

Constructing 2D/3D perovskite heterojunctions is effective for the surface passivation of perovskite solar cells (PSCs). However, previous reports that studying perovskite post-treatment only physically deposits 2D perovskite on the 3D perovskite, and the bulk 3D perovskite remains defective. Herein, we propose Cl2-dissolved chloroform as a multifunctional solvent for concurrently constructing 2D/3D perovskite heterojunction and inducing the secondary growth of the bulk grains. The mechanism of how Cl2 affects the performance of PSCs is clarified. Specifically, the dissolved Cl2 reacts with the 3D perovskite, leading to Cl/I ionic exchange and Ostwald ripening of the bulk grains. The generated Cl− further diffuses to passivate the bulk crystal and buried interface of PSCs. Hexylammonium bromide dissolved in the solvent reacts with the residual PbI2 to form 2D/3D heterojunctions on the surface. As a result, we achieved high-performance PSCs with a champion efficiency of 24.21% and substantially improved thermal, ambient, and operational stability. Constructing 2D/3D perovskite heterojunctions is effective for the surface passivation of perovskite solar cells. Here, the authors apply Cl2-dissolved chloroform as a multifunctional solvent and achieve a champion device efficiency of 24.21% with improved thermal, ambient and operational stability. [ABSTRACT FROM AUTHOR]

The under‐coordinated defects within perovskite and its relevant interfaces always attract and trap the free carriers via the electrostatic force, significantly limiting the charge extraction efficiency and the intrinsic stability of perovskite solar cells (PSCs). Herein, self‐diffusion interfacial doping by using ionic potassium L‐aspartate (PL‐A) is first reported to restrain the carrier trap induced recombination via the reconstruction of energy level structure at SnO2/perovskite interface in conventional n‐i‐p structured PSCs. Experiments and theories are consistent with the PL‐A anions that can remain at the SnO2 surface due to strong chemical adsorption. During the spin‐coating of the perovskite film, the cations gradually diffuse into perovskite and endow an n‐doping effect, which provides higher force and a better energy level alignment for the carrier transport. As a result, they obtained 23.74% power conversion efficiency for the PL‐A modified small‐area devices, with dramatically improved open‐circuit voltage of 1.19 V. The corresponding large‐area devices (1.05 cm2) achieved an efficiency of 22.23%. Furthermore, the modified devices exhibited negligible hysteresis and enhanced ambient air stability exceeding 1500 h. [ABSTRACT FROM AUTHOR]

Designing functional fullerenes with roles beyond defect passivation and electron‐transporting for perovskite solar cells (PSCs) is essential to the development of fullerenes and PSCs. Here, the authors design and synthesize a functional fullerene, FPD, composed of a C60 cage, a porphyrin ring, and three pentafluorophenyl groups. The structure features of FPD enable it can form chemical interactions with the perovskite lattices. These interactions enhance the defect passivation effect and prevent the decomposition of perovskite under irradiation. As a result, the FPD‐based device yields an improved power conversion efficiency of 23% with substantially enhanced operational stability (T80 > 1500 h). Furthermore, once got damaged, the FPD can prevent lead leakage by forming a stable and water‐insoluble complex (FPD‐Pb). Their findings provide a novel strategy to achieve high‐performance and eco‐friendly PSCs with functional fullerene materials. [ABSTRACT FROM AUTHOR]

Preparation of phase-pure and stable formamidinium-based lead iodide (FAPbI3) perovskites is essential for fabricating high-performance perovskite solar cells (PSCs). Here, we report using very little CsPbBr3 perovskite (2%, molar ratio to FAPbI3) to stabilize the black-phase α-FAPbI3. Specifically, the as-synthesized CsPbBr3 powder is added to the PbI2 precursor. It is found that the interlayer spacing of layered PbI2 can be stretched due to the formation of the PbI2–DMSO–CsPbBr3 intermediate phase, which can promote the penetration of FAI and the transformation to black phase α-FAPbI3. The incorporation of CsPbBr3 not only stabilizes the FAPbI3 phase but also results in a high-quality film with increased grain size and suppressed bulk defects. Therefore, the resultant PSCs exhibit enhanced built-in potential, improved carrier extraction, and suppressed non-radiative recombination. As a result, the corresponding PSCs deliver a champion efficiency of 23.34%. Moreover, the PSCs stabilized with CsPbBr3 show much improved operational stability, retaining 80% of their initial efficiency after 1153 hours following the maximum power point (MPP) tracking under one sun illumination; while the efficiencies of control devices w/o CsPbBr3 drop to 80% of their initial efficiencies after 75 hours. [ABSTRACT FROM AUTHOR]

Tin oxide (SnO2) is widely used as an electron transport layer (ETL) to fabricate planar perovskite solar cells (PSCs) due to their easy and low‐temperature processed fabrication. Enhancing carrier extraction and energy level alignment at the perovskite/SnO2 interface is vital to improve the device performance further. Here, we demonstrate a double‐layered SnO2/ NH4Cl‐SnO2 as an efficient ETL. The top NH4Cl‐SnO2 shows a better energy level alignment with the perovskite and reduced alkalinity to avoid perovskite degradation, resulting in enhanced electron extraction efficiency and interfacial stability. Furthermore, the bottom SnO2 retains the capability of efficient carrier transport to avoid charge accumulation. As a result, we achieve a champion device with a power conversion efficiency of 21.01% and negligible hysteresis. Moreover, the corresponding PSCs show much improved operational stability, retaining 80% of the initial efficiency after 1090 hours of operation at the maximum power point under 1‐sun illumination. While the pristine SnO2 based PSCs only insist on 278 hours before losing 20% of the initial efficiency. [ABSTRACT FROM AUTHOR]

It is challenging to passivate defects that are buried in the depth of perovskite films; most of the reported passivation methods cannot reach the deep defects. Herein, methanol is adopted as a dual‐functional reagent to not only act as a solvent but also help the dissolved ions penetrate the depth of perovskite films. By treating the as‐prepared perovskite films with CsBr/methanol solution, Br− ions can react with the undercoordinated Pb2+, and Cs+ ions can fill in the cation vacancies. This strategy enables surface and bulk defects passivation to be achieved simultaneously. The nonradiative recombination of the double‐passivated devices is significantly suppressed and the migration of charged defects is remarkably hindered. As a result, an improved power conversion efficiency of 19.5% and an open‐circuit voltage of 1.183 V is achieved. Moreover, the passivated device can retain ≈80% of the initial efficiency after working for 500 h at maximum power point under 1‐sun illumination, whereas the pristine device reaches 80% of the initial efficiency after only 90 h. This work demonstrates that surface and bulk defects passivation is critical to improve the efficiency and long‐term operational stability of the perovskite solar cells. [ABSTRACT FROM AUTHOR]

Fullerene derivatives, especially after purposely functionalization, have potential to efficiently passivate interfacial defects between perovskites and electron transport layers. In this work, a fullerene derivative with amine functional group, 2,5‐diphenyl C60 fulleropyrrolidine (DPC60), is synthesized and employed as an interfacial layer between a perovskite and SnO2 in planar perovskite solar cells (PSCs). The cis‐configuration and the specific amine group of DPC60 effectively enhance the chemical interaction between the perovskite and DPC60, promoting the passivation of perovskite defects at the interface. The suitable energy level of DPC60 and the improved conductivity of the SnO2/DPC60 film facilitate the electron extraction from the perovskite layer. As a result, PSCs incorporated with DPC60 reach a PCE of 20.4% with high reproducibility, which is much higher than that of the bare SnO2 based devices (18.8%). Furthermore, the hydrophobic DPC60 layer suppresses heterogeneous nucleation and improves the crystallinity of the perovskite film, resulting in better device stability, retaining 82% of its initial efficiency after 200 h of 1 sun continuous irradiation and thermal ageing (55 ± 5 °C). [ABSTRACT FROM AUTHOR]

Understanding the role of individual cation and halide components in the intrinsic long-term stability of perovskite solar cells (PSCs) is of great importance to pursue devices with high efficiency and superior long-term stability simultaneously. In this work, we report a low dopant content (1%) doping strategy to reveal the role of individual bromide and methylammonium (MA) in the intrinsic operational stability of formamidinium lead iodide (FAPbI3-based) PSCs. This strategy enables us to tune the trap density of perovskite films while keeping their apparent morphological and optical properties unchanged. Our results demonstrate that the incorporation of MA into FAPbI3-based PSCs is harmful to their long-term stability due to defect-induced degradation. And Br incorporation is beneficial for enhancing the stability of FAPbI3-based PSCs via suppressing the trap density in perovskite films. This work highlights the importance of defect management in improving the long-term operational stability of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Fullerene derivatives are considered excellent materials for the extraction and transportation of electrons in the production of efficient tin-based perovskite solar cells (TPSCs). However, it is not clear how the molecular structure of fullerene derivatives affects the efficiency and stability of TPSCs. In this study, the effects of fullerene derivatives, (6,6)-phenyl-C61-butyric acid hexyl ester (PCBH) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM), with different functional groups, on photovoltaic performance were investigated. The flexible alkyl chain of PCBH effectively improved the film morphology and stability, the electron extraction and transport capabilities, and the interface contact of fullerene and perovskite. As a result, the PCBH-based TPSC yielded a higher efficiency, of 9.21%, than the PCBM-based devices (7.54%). More importantly, the PCBH-based films exhibited higher stability and effectively suppressed the oxidation of Sn2+ by inhibiting oxygen permeation. Therefore, the PCBH-based devices exhibited significantly enhanced stability. This result indicates that optimizing the functional group of fullerene derivatives is crucial for improving the efficiency and stability of TPSCs. [ABSTRACT FROM AUTHOR]

Recently, low-bandgap formamidinium lead iodide FAPbI 3 -based perovskites are of particular interest for high-performance perovskite solar cells (PSCs) due to their broad spectral response and high photocurrent output. However, to inhibit the spontaneous α-to-δ phase transition, 15-17% (molar ratio) of bromide and cesium or methylammonium incorporated into the FAPbI 3 are indispensable to achieve efficient PSCs. In return, the high bromide content will increase bandgap and narrow the spectral response region. If simply reducing the bromide content, the corresponding PSCs exhibit inferior operational stability due to α-to-δ phase transition, interface degradation, and halide migration. Herein, we report a CsPbBr 3 -cluster assisted vertically bottom-up crystallization approach to fabricate low-bromide (1% ∼ 6%), α-phase pure, and MA-free FAPbI 3 -based PSCs. The clusters, in the size of several nanometers, could act as nuclei to facilitate vertical growth of high quality α-FAPbI 3 perovskite crystals. Moreover, these clusters can show further intake by perovskite after thermal annealing, which improves the phase homogeneity of the as-prepared perovskite films. As a result, the corresponding mesoporous PSCs deliver a champion efficiency of 21.78% with photoresponse extended to 830 nm. Moreover, these devices show remarkably improved operational stability, retaining ∼82% of the initial efficiency after 1,000 h of maximum power point tracking under 1 sun condition.