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Developing an additive to effectively regulate the perovskite crystallization kinetics for the optimized optoelectronic properties of perovskite film plays a vital role in obtaining high efficiency and stable perovskite solar cells (PSCs). Herein, a new additive is designed and directly synthesized in perovskite precursor solution by utilizing an addition reaction between but-3-yn-1-amine hydrochloride (BAH) and formamidinium iodide. It is found that its product may control the intermediate precursor phase for regulating perovskite nucleation, leading to advantageous 2D perovskite to induce growth of perovskite along the preferred [001] orientation with not only released lattice strain but also strong interaction with perovskite to passivate its surface defects. By taking advantage of the above synergistic effects, the optimized PSC delivers an efficiency of 25.19% and a high open-circuit voltage (V OC ) of 1.22 V. Additionally, the devices demonstrate good stability, remaining over 90% of their initial efficiencies under ambient atmosphere conditions for 60 days, high temperature of 85 °C for 200 h, or maximum power point tracking for 500 h., (© 2024 Wiley‐VCH GmbH.)

The success of Y6-type nonfullerene small molecule acceptors (NF-SMAs) in polymer solar cells (PSCs) can be attributed to their unique honeycomb stacking style, which leads to favorable thin-film morphologies. The intermolecular interactions related to the crystallization tendency of these NF-SMAs is closely governed by their electron accepting end groups. For example, the high performance Y6 derivative L8-BO (BTP-4F) presents three types of stacking modes in contrast to two stacking modes of Y6. Hence, it is ultimately interesting to obtain more insight on the packing properties and the preferences influenced by chemical modifications such as end group engineering. This work designs and synthesizes asymmetric and symmetric L8-BO derivatives with brominated end groups and explores the stacking preferences in various modes. The asymmetric BTP-3FBr displays an optimized crystallization tendency and thin film morphology, leading to a decent power conversion efficiency (PCE) of 18.34% in binary devices and a top PCE of 19.32% in ternary devices containing 15 wt% IDIC as the second acceptor., (© 2023 Wiley-VCH GmbH.)

The limited selection of wide bandgap polymer donors for all-polymer solar cells (all-PSCs) is a bottleneck problem restricting their further development and remains poorly studied. Herein, a new wide bandgap polymer, namely PBBTz-Cl, is designed and synthesized by bridging the benzobisthiazole acceptor block and chlorinated benzodithiophene donor block with thiophene units for application as an electron donor in all-PSCs. PBBTz-Cl not only possesses wide bandgap and deep energy levels but also displays strong absorption, high-planar structure, and good crystallinity, making it a promising candidate for application as a polymer donor in organic solar cells. When paired with the narrow bandgap polymer acceptor PY-IT, a fibril-like morphology forms, which facilitates exciton dissociation and charge transport, contributing to a power conversion efficiency (PCE) of 17.15% of the corresponding all-PSCs. Moreover, when introducing another crystalline polymer acceptor BTP-2T2F into the PBBTz-Cl:PY-IT host blend, the absorption ditch in the range of 600-750 nm is filled, and the blend morphology is further optimized with the trap density reducing. As a result, the ternary blend all-PSCs achieve a significantly improved PCE of 18.60%, which is among the highest values for all-PSCs to date., (© 2023 Wiley-VCH GmbH.)

Judicious tailoring of the interface between the SnO 2 electron-transport layer and the perovskite buried surface plays a pivotal role in obtaining highly efficient and stable perovskite solar cells (PSCs). Herein, a DL-carnitine hydrochloride (DL) is incorporated into the perovskite/SnO 2 interface to suppress the defect-states density. A DL-dimer is obtained at the interface by an intermolecular esterification reaction. For the SnO 2 film, the Cl - in the DL-dimer can passivate oxygen vacancies (V O ) through electrostatic coupling, while the N in the DL-dimer can coordinate with the Sn 4+ to passivate Sn-related defects. For the perovskite film, the DL-dimer can passivate FA + defects via hydrogen bonding and Pb-related defects more efficiently than the DL monomer. Upon DL-dimer modification, the interfacial defects are effectively passivated and the quality of the resultant perovskite film is improved. As a result, the DL-treated device achieves a gratifying open-circuit voltage (V OC ) of 1.20 V and a champion power conversion efficiency (PCE) of 25.24%, which is a record value among all the reported FACsPbI 3 PSCs to date. In addition, the unencapsulated devices exhibit a charming stability, sustaining 99.20% and 90.00% of their initial PCEs after aging in air for 1200 h and continuously operating at the maximum power point tracking for 500 h, respectively., (© 2023 Wiley-VCH GmbH.)

Cesium lead triiodide (CsPbI 3 ) is a promising light-absorbing material for constructing perovskite solar cells (PSCs) owing to its favorable bandgap and thermal tolerance. However, the high density of defects in the CsPbI 3 film not only act as recombination centers, but also facilitate ion migration, leading to lower PCE and inferior stability compared with the state-of-the-art organic-inorganic hybrid PSC counterpart. Theoretical analyses suggest that the effective suppression of defects in CsPbI 3 film is helpful for improving the device performance. Herein, the stable and efficient γ -CsPbI 3 PSCs are demonstrated by developing an acyloin ligand (1,2-di(thiophen-2-yl)ethane-1,2-dione (DED)) as a phase stabilizer and defect passivator. The experiment and calculation results confirm that carbonyl and thienyl in DED can synergistically interact with CsPbI 3 by forming a chelate to effectively passivate Pb-related defects and further suppress ion migration. Consequently, DED-treated CsPbI 3 PSCs yield a champion PCE of 21.15%, which is one of the highest PCE among all the reported CsPbI 3 PSCs to date. In addition, the unencapsulated DED-CsPbI 3 PSC can retain 94.9% of itsinitial PCE when stored under ambient conditions for 1000 h and 92.8% of its initial PCE under constant illumination for 250 h., (© 2023 Wiley-VCH GmbH.)

Raising the lowest unoccupied molecular orbital (LUMO) energy level of Y-type non-fullerene acceptors can increase the open-circuit voltage (V oc ) and thus the photovoltaic performance of the current top performing polymer solar cells (PSCs). One of the viable routes is demonstrated by the successful Y6 derivative of L8-BO with the branched alkyl chains at the outer side. This will introduce steric hindrance and reduce intermolecular aggregation, thus open up the bandgap and raise the LUMO energy level. To take further advantages of the steric hindrance influence on optoelectronic properties of Y6 derivatives, two Y-type non-fullerene acceptors of BTP-Cy-4F and BTP-Cy-4Cl are designed and synthesized by adopting outer branched side chains and inner cyclohexane side chains. An outstanding V oc of 0.937 V is achieved in the D18:BTP-Cy-4F binary blend devices along with a power conversion efficiency (PCE) of 18.52%. With the addition of BTP-eC9 to extend the absorption spectral coverage, a remarkable PCE of 19.36% is realized finally in the related ternary blend devices, which is one of the highest values for single-junction PSCs at present. The results illustrate the great potential of cyclohexane side chains in constructing high-performance non-fullerene acceptors and their PSCs., (© 2023 Wiley-VCH GmbH.)

The morphology plays a key role in determining the charge generation and collection process, thus impacting the performances of organic solar cells (OSCs). The limited selection pool of additives to optimize the morphology of OSCs, especially for the emerging layer-by-layer (LbL) OSCs, impeding the improvements of photovoltaic performances. Herein, a new method of using conjugated polymers as the additives to optimize the morphology for improving the photovoltaic performances of LbL-OSCs is reported. Four polymers of PH, PS, PF, and PCl are developed with different side chains. These polymers exhibit poor performances as donor materials and additives in the BHJ devices, due to the unsuitable energy level alignment and unfavorable molecular interactions. By contrast, they can be served as efficient additives to optimize the PM6 fibril matrix for facilitating the penetration of BTP-eC9 and forming an intertwined D/A bicontinuous network with a vertical segregation. Such morphology is optimized by side chain engineering, which enables the progressive improvement of the charge separation and collection. As a result, adding a small amount of PCl as the additive, the optimized morphology contributes to a champion PCE of 19.10% with a high FF of 80.5%., (© 2022 Wiley-VCH GmbH.)

Flexible perovskite solar cells (f-PSCs) have attracted great attention because of their unique advantages in lightweight and portable electronics applications. However, their efficiencies are far inferior to those of their rigid counterparts. Herein, a novel histamine diiodate (HADI) is designed based on theoretical study to modify the SnO 2 /perovskite interface. Systematic experimental results reveal that the HADI serves effectively as a multifunctional agent mainly in three aspects: 1) surface modification to realign the SnO 2 conduction band upward to improve interfacial charge extraction; 2) passivating the buried perovskite surface, and 3) bridging between the SnO 2 and perovskite layers for effective charge transfer. Consequently, the rigid MA-free PSCs based on the HADI-SnO 2 electron transport layer (ETL) display not only a high champion power conversion efficiency (PCE) of 24.79% and open-circuit voltage (V OC ) of 1.20 V but also outstanding stability as demonstrated by the PSCs preserving 91% of their initial efficiencies after being exposed to ambient atmosphere for 1200 h without any encapsulation. Furthermore, the solution-processed HADI-SnO 2 ETL formed at low temperature (100 °C) is utilized in f-PSCs that achieve a PCE as high as 22.44%, the highest reported PCE for f-PSCs to date., (© 2022 Wiley-VCH GmbH.)

A wide bandgap small molecular acceptor, SFBRCN, containing a 3D spirobifluorene core flaked with a 2,1,3-benzothiadiazole (BT) and end-capped with highly electron-deficient (3-ethylhexyl-4-oxothiazolidine-2-yl)dimalononitrile (RCN) units, has been successfully synthesized as a small molecular acceptor (SMA) for nonfullerene polymer solar cells (PSCs). This SMA exhibits a relatively wide optical bandgap of 2.03 eV, which provides a complementary absorption to commonly used low bandgap donor polymers, such as PTB7-Th. The strong electron-deficient BT and RCN units afford SFBRCN with a low-lying LUMO (lowest unoccupied molecular orbital) level, while the 3D structured spirobifluorene core can effectively suppress the self-aggregation tendency of the SMA, thus yielding a polymer:SMA blend with reasonably small domain size. As the results of such molecular design, SFBRCN enables nonfullerene PSCs with a high efficiency of 10.26%, which is the highest performance reported to date for a large bandgap nonfullerene SMA., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel-small molecular acceptor with electron-deficient 1,3,5-triazine as the core and perylene diimides as the arms is developed as the acceptor material for efficient bulk heterojunction organic solar cells with an efficiency of 9.15%., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)