Chen Weijie

A p-chlorobenzenesulfonic acid (CBSA)-based self-assembled layer dual-passivation strategy is employed to effectively eliminate interfacial lattice mismatch and detrimental reactions in NiO _x -based perovskite solar cells, which achieves unencapsulated devices preserving above 80% of initial efficiencies after storing in N₂ for 3000 h, in air with a relative humidity of 50–70% for 1000 h, and heating at 85 °C for 800 h, respectively.

Abstract

Interfacial lattice mismatch and adverse reaction are the key issues hindering the development of nickel oxide (NiO _x )-based inverted perovskite solar cells (PVSCs). Herein, a p-chlorobenzenesulfonic acid (CBSA) self-assembled small-molecule (SASM) is adopted to anchor NiO _x and perovskite crystals to endow dual-passivation. The chlorine terminal of SASMs can provide growth sites for perovskite, leading to interfacial strain release. Meanwhile, the sulfonic acid group from SASMs can passivate surface defects of NiO _x , conducive to charge carrier extraction. In addition, the self-assembled layer inhibits the adverse interfacial reaction by preventing NiO _x contact with perovskite. Therefore, the NiO _x /CBSA-based PVSCs obtain a champion power conversion efficiency (PCE) of 21.8%. Of particular note, the unencapsulated devices can retain above 80% of their initial PCE values after storage in a nitrogen atmosphere for 3000 h, in air with a relative humidity of 50–70% for 1000 h, and heating at 85 °C for 800 h, respectively.

A combined precrystallization and metal ion surface modification strategy has enabled the room temperature and cost-effective fabrication of high-quality SnO₂ electron transport layer for effectively accelerating charge extraction and suppressing charge recombination in flexible perovskite photovoltaics, achieving improved efficiencies up to 19.3% and remarkable mechanical strength.

Abstract

Room temperature-processed electron transport layers (RT-ETLs) demonstrate vast potential to be used in fabricating high-performance flexible perovskite solar cells (PSCs) in an energy-saving manner. However, the RT-ETL normally suffers from inferior crystallinity, mismatched energy level, and high surface trap-state density, which would result in under-optimized interfacial electron extraction and undesirable interfacial charge recombination at ETL/perovskite interface, thus limiting the device performance. Herein, a novel strategy is demonstrated to prepare annealing-free RT-ETL based on precrystalline metal ion-modified SnO₂ nanocrystals, which perfectly optimizes the interfacial energy level alignment between ETL and perovskite layer, achieving nearly zero-barrier charge transfer at the interface. As a result, the charge extraction has been remarkably accelerated and the interfacial charge recombination has been largely suppressed, leading to a ≈26% enhancement in device efficiency. The best-performing flexible PSCs achieve efficiencies up to 19.3%, accompanied by outstanding mechanical strength under repeated bending cycle tests, which, to the best of the knowledge, is one of the highest reported values for the flexible perovskite photovoltaics fabricated with RT-ETLs.

A solid–solid contact strategy is proposed to form an ultra-thin multifunctional ion-lock interface layer in PSCs. This dense Nafion layer can lock the ions migration between perovskite and CTLs and eliminate the surface defects/traps of perovskite. The PSCs with Nafion multifunctional ion-lock interface layer show a high efficiency of 23.13% with excellent humidity and operational stability.

Abstract

It has been a hindering issue in perovskite solar cells that the interfaces between the perovskite and charge transport layers show significantly high concentrations of defects with an amount about 100 times more than inside the bulk perovskite layer. The issue causes substantial reduction in both the efficiency and stability of the devices. Herein, a solid–solid contact approach is demonstrated to realize a multifunctional ion-lock layer with strong chemical interaction to the perovskite layer. The multifunctional ion-lock layer remarkably suppresses the interface defects and tunes the work function, contributing to promoting the carrier extraction, increasing the open-circuit voltage, and enlarging the photocurrent. In addition, the multifunctional ion-lock layer successfully locks ions from movement and thus improves the stability of the devices. Finally, with a multifunctional ion-lock layer, the perovskite solar cells deliver an efficiency of up to 23.13% along with desirable long-term operational, storage, and humidity stability. Consequently, the work offers guidelines for establishing defect-suppressed interfaces between perovskites and hole transport layers.

A vinylene-linker-based polymer acceptor (PY-V-γ) with rigid and coplanar chain conformations is synthesized, exhibiting redshifted absorption and ordered packing. When employed in all-polymer solar cells, the PY-V-γ-based devices yield a higher efficiency of 17.1% than PY-T-γ- and PY-2T-γ-based ones and exhibit robust mechanical stability in flexible devices, suggesting the potential for commercial application.

Abstract

State-of-art Y-series polymer acceptors are typically based on a mono-thiophene linker, which can cause some twisted molecular conformations and thus limit the performance of all-polymer solar cells (all-PSCs). Here, a high-performance polymer acceptor based on vinylene linkers is reported, which leads to surprising changes in the polymers’ molecular conformations, optoelectronic properties, and enhanced photovoltaic performance. It is found that the polymer acceptors based on thiophene or bithiophene linkers (PY-T-γ and PY-2T-γ) display significant molecular twisting between end-groups and linker units, while the vinylene-based polymer (PY-V-γ) exhibits a more coplanar and rigid molecular conformation. As a result, PY-V-γ demonstrates a better conjugation and tighter interchain stacking, which results in higher mobility and a reduced energetic disorder. Furthermore, detailed morphology investigations reveal that the PY-V-γ-based blend exhibits high domain purity and thus a better fill factor in its all-PSCs. With these, a higher efficiency of 17.1% is achieved in PY-V-γ-based all-PSCs, which is the highest efficiency reported for binary all-PSCs to date. This work demonstrates that the vinylene-linker is a superior unit to build polymer acceptors with more coplanar and rigid chain conformation, which is beneficial for polymer aggregation and efficient all-PSCs.

The solid additive, 1,4-diiodobenzene (DIB), has a high competence to optimize the vertical morphology of bulk heterojunction active layer, resulting in a high efficiency of 18.7% with a open-circuit voltage (V _OC) of 0.922 V, a short-circuit current (J _SC) of 26.6 mA cm⁻², and a fill factor (FF) of 75.6% for DIB-processed D18-Cl/L8-BO binary devices.

Abstract

The tuning of vertical morphology is critical and challenging for organic solar cells (OSCs). In this work, a high open-circuit voltage (V _OC) binary D18-Cl/L8-BO system is attained while maintaining the high short-circuit current (J _SC) and fill factor (FF) by employing 1,4-diiodobenzene (DIB), a volatile solid additive. It is suggested that DIB can act as a linker between donor or/and acceptor molecules, which significantly modifies the active layer morphology. The overall crystalline packing of the donor and acceptor is enhanced, and the vertical domain sizes of phase separation are significantly decreased. All these morphological changes contribute to exciton dissociation, charge transport, and collection. Therefore, the best-performing device exhibits an efficiency of 18.7% with a V _OC of 0.922 V, a J _SC of 26.6 mA cm⁻², and an FF of 75.6%. As far as it is known, the V _OC achieved here is by far the highest among the reported OSCs with efficiencies over 17%. This work demonstrates the high competence of solid additives with two iodine atoms to tune the morphology, particularly in the vertical direction, which can become a promising direction for future optimization of OSCs.

A low-cost, high volatile, and asymmetric halogen benzene derivate, 1,3-dibromo-5-chlorobenzene, is applied as process-aid solid to manipulate the blend nanomorphology and enhance the crystallinity in Y-series small molecule-based photoactive layer system. A champion power conversion efficiency of 17.0% is yielded, which is one of the highest performances for thick-film organic solar cells.

Abstract

Volatile solids with symmetric π-backbone are intensively implemented on manipulating the nanomorphology for improving the operability and stability of organic solar cells. However, due to the isotropic stacking, the announced solids with symmetric geometry cannot modify the microscopic phase separation and component distribution collaboratively, which will constrain the promotion of exciton splitting and charge collection efficiency. Inspired by the superiorities of asymmetric configuration, a novel process-aid solid (PAS) engineering is proposed. By coupling with BTP core unit in Y-series molecule, an asymmetric, volatile 1,3-dibromo-5-chlorobenzene solid can induce the anisotropic dipole direction, elevated dipole moment, and interlaminar interaction spontaneously. Due to the synergetic effects on the favorable phase separation and desired component distribution, the PAS-treated devices feature the evident improvement of exciton splitting, charge transport, and collection, accompanied by the suppressed trap-assisted recombination. Consequently, an impressive fill factor of 80.2% with maximum power conversion efficiency (PCE) of 18.5% in the PAS-treated device is achieved. More strikingly, the PAS-treated devices demonstrate a promising thickness-tolerance character, where a record PCE of 17.0% is yielded in PAS devices with a 300 nm thickness photoactive layer, which represents the highest PCE for thick-film organic solar cells.

The authors show that a twisted acceptor-donor-acceptor type compound forms mostly-amorphous phases in the as-cast film but can be readily converted into more crystalline domains by means of thermal annealing. As a result, strong crystallization during thin-film coating is limited, leading to the finely phase-separated morphology needed for organic photovoltaics.

Abstract

Molecular aggregation and crystallization during film coating play a crucial role in the realization of high-performing organic photovoltaics. Strong intermolecular interactions and high solid-state crystallinity are beneficial for charge transport. However, fast crystallization during thin-film drying often limits the formation of the finely phase-separated morphology required for efficient charge generation. Herein, the authors show that twisted acceptor-donor-acceptor (A-D-A) type compounds, containing an indacenodithiophene (IDT) electron-rich core and two naphthalenediimide (NDI) electron-poor units, leads to formation of mostly amorphous phases in the as-cast film, which can be readily converted into more crystalline domains by means of thermal annealing. This design strategy solves the aforementioned conundrum, leading to an optimal morphology in terms of reduced donor/acceptor domain-separation sizes (ca. 13 nm) and increased packing order. Solar cells based on these acceptors with a PBDB-T polymer donor show a power conversion efficiency over 10% and stable morphology, which results from the combined properties of desirable excited-state dynamics, high charge mobility, and optimal aggregation/crystallization characteristics. These results demonstrate that the twisted A-D-A motif featuring thermally-induced crystallization behavior is indeed a promising alternative design approach toward more morphologically robust materials for efficient organic photovoltaics.

The universal growth of ultrathin perovskite single crystals is realized by designing an oriented solvent microenvironment induced by the interfacial electric field originated from the charge separation between solid and liquid phases. Such a strategy can fabricate a wide range of high-quality ultrathin perovskite single crystals, from layered to nonlayered, organic to inorganic, and toxic to low-toxic lead-free perovskite. Notably, the realization of high quality and diversity of ultrathin perovskites will facilitate both fundamental studies and optoelectronic applications.

Abstract

Perovskites have engaged significant attention owing to rich species and remarkable physical properties as well as optoelectronic applications. Compared to bulk counterparts, ultrathin perovskites exhibit more available compositions due to the breaking of bulk lattice limitation. Coupled with crystal lattice relaxation and quantum confinement, infinite intriguing properties of ultrathin perovskites deserve to be explored. Developing ultrathin perovskites with alterable composition and structure is a necessity to fully explore this versatile family. Herein, a universal strategy is conceived via constructing oriented solvent microenvironment induced by the interfacial electric field originated from the charge separation between solid and liquid phases, which is conducive to controlling the precursor distribution and makes crystals preferentially nucleate and grow in the preferentially lateral mode. From layered to nonlayered, organic to inorganic, and toxic to low-toxic lead-free perovskite, a full-range synthesis is achieved of ultrathin perovskites. This work opens up opportunities both for ultrathin perovskite exploration through compositional engineering and for device miniaturization in energy conversion applications.

Three oligomeric acceptors were synthesized in this work. Investigations revealed that oligomer acceptor-based devices showed much better photovoltaic performance and light-soaking stability than small molecules and polymers. dBTICγ-EH, a dimer, showed a power conversion efficiency (PCE) of 16.06 % in Q-PHJ devices with superior device stability, which is the highest value among the reported oligomeric acceptors to date.

Abstract

Oligomeric acceptors are expected to combine the advantages of both highly developed small molecular and polymeric acceptors. However, organic solar cells (OSCs) based on oligomers lag far behind due to their slow development and low diversity. Here, three oligomeric acceptors were produced through oligomerization of small molecules. The dimer dBTICγ-EH achieved the best power conversion efficiencies (PCEs) of 14.48 % in bulk heterojunction devices and possessed a T80 (80 % of the initial PCE) lifetime of 1020 h under illumination, which were far better than that of small molecular and polymeric acceptors. More excitingly, it showed PCEs of 16.06 % in quasi-planar heterojunction (Q-PHJ) devices which is the highest value OSCs using oligomeric acceptors to date. These results suggest that oligomerization of small molecules is a promising strategy to achieve OSCs with optimized performance between the high efficiency and durable stability, and offer oligomeric materials a bright future in commercial applications.

Hydrophobic graphene quantum dots (HGQDs) containing amide linkages, which consist of carbonyl and dodecyl amine groups, are successfully applied as an efficient bifunctional interface modifier to simultaneously boost the power conversion efficiency and stability of perovskite solar cells.

Passivating the defects and grain boundaries (GBs) of perovskite films at the interface by interface engineering is a promising route to achieve efficient and stable perovskite solar cells (PSCs). Herein, a new type of graphene, that is, hydrophobic graphene quantum dots (HGQDs) containing amide linkages, which consist of carbonyl and dodecyl amine groups, is successfully used as a bifunctional interface modifier to engineer the interface of the perovskite/hole transport layer. A comprehensive characterization including X-ray photoelectron spectroscopy, Fourier-transform photocurrent spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and space-charge-limited current measurements is performed to identify the underlying passivation mechanisms. It can be demonstrated that the HGQDs, due to the bifunctional groups containing N and O atoms, effectively passivate the uncoordinated Pb²⁺ ions at the perovskite film surface and GBs and consequently induce a lower trap state density. Moreover, HGQDs enhance the quality of the perovskite film which reduces the charge recombination at the interface. Therefore, the power conversion efficiency of PSCs treated with HGQDs is significantly increased from 16.00% to 18.30%, mainly based on the improved open-circuit voltage and fill factor. Importantly, the HGQDs featuring hydrophobicity due to alkyl chains significantly enhance moisture stability.

This paper describes the impacts of sequential halogenation in selective positions of small molecule acceptors on the blend morphology, voltage loss, and photovoltaic performances. The A4-based organic solar cells exhibit the highest power conversion efficiency of 17.2%, attributed to the optimized blend morphology and reduced voltage loss.

Abstract

Herein, the impacts of the selective halogenation at two different positions of dicyanomethylene-3-indanone (IC) end groups and inner side chains of small molecular acceptors (SMAs) on the P _D:SMA interfacial interactions, blend morphology, and resulting photovoltaic properties are described. In this study, four different SMAs (A1, A2, A3, and A4) with the same molecular backbone, but with different degrees of halogenation, are synthesized. The IC end groups on the backbones of the A1 and A3, and A2 and A4 SMAs are chlorinated and fluorinated, respectively; in addition, 6-phenoxyhexyl inner side chains of the A3 and A4 are chlorinated. The SMAs are paired with a chlorinated PBDT-Cl P _D to construct organic solar cells (OSCs). The PBDT-Cl:A4-based OSC exhibits the highest power conversion efficiency of 17.2%, outperforming the PBDT-Cl:A1-(13.3%), PBDT-Cl:A2-(15.6%), and PBDT-Cl:A3-based OSC (16.5%). The Cl atoms on the side chains in the A3 and A4 SMAs enhance the molecular/energetic interactions at the P _D:SMA interfaces and improve the blend morphology in terms of domain purity and spacing. These effects lead to the improved fill factors and reduced voltage loss of the PBDT-Cl:A3- and PBDT-Cl:A4-based OSCs. This study demonstrates the importance of appropriate halogenation of SMAs in optimizing the blend morphology, reducing voltage loss, and improving OSC performance.