Chen Weijie

Intermolecular non-covalent interactions improve the planarity of the central moiety of DCT, resulting in a more densely packed molecular arrangement, and thus a high hole mobility. Devices based on dopant-free DCT exhibit a high efficiency of 22.50%, with excellent stability.

Abstract

Hole transport materials (HTMs) have a critical impact on the performance of perovskite solar cells (PSCs). Especially, the dopant-free HTMs could avoid the usage of hygroscopic dopants and reduce costs, which are important for device stability. Most of the current organic dopant-free HTMs are polycyclic aromatic hydrocarbons-based planar conjugated structures. Yet, the synthesis of conjugated fused heterocycles is often complicated. In this work, intramolecular non-covalent interaction is introduced to construct two organic HTMs (DCT and DTC), which can be facilely obtained through simple reactions. Compared to DTC with hexyl chain on the central benzene ring, DCT with hexyloxy chains shows better planarity in the core structure, as a result of the intramolecular non-covalent interactions between oxygen on hexyloxy and sulfur atom on the adjacent thiophene, as reflected from its single crystal structure. Moreover, DCT in a pristine state shows a decent hole mobility comparable to the doped Spiro-OMeTAD. Ultimately, conventional devices using dopant-free DCT as HTM show a high efficiency of 22.50%, with excellent long-term stability, and light and thermal stability. The results show that the noncovalent interaction is a useful and simple design strategy for dopant-free HTMs, that can effectively improve the efficiency and stability of PSCs.

The PbS interconnect layer is constructed to optimize lattice and energy level mismatch problems between SnO₂ and buried perovskite, which achieves a high efficiency of 24.24%.

Abstract

In n-i-p type perovskite solar cells (PSCs), mismatches in energy level and lattice at the buried interface is highly detrimental to device performance. Here, thin PbS interconnect layer in situ coating on the SnO₂ surface is grown. The function of PbS at the interface is different from the commonly used function of crystalline seeds in perovskite bulk. The theoretical calculation show that it helps construct an interconnect structure of SnO₂/PbS/Perovskite with matched energy level and lattice. This not only increases conductivity of SnO₂, but also upshifts Fermi energy levels (E _F) of both SnO₂ and buried perovskite due to charge transfer and perovskite's internal defect changes. Such a suitable energy level arrangement ensures a better energy level match at the interface, favoring efficient charge transfer and less open circuit voltage (V _oc) loss. Additionally, in situ PL reveals that the template effect of PbS enable perovskite grain to grow bottom-up because of their highly matched lattice parameters. This growth mode optimizes buried interface contact and crystallinity of perovskite. Ultimately, after PbS modification, a remarkable power conversion efficiency (PCE) exceeding 24% and better device stability are obtained. This work demonstrates an effective interconnect layers strategy to realize ideal interface contact toward high-performance PSCs.

The primary challenges related to Sn-based perovskite solar cells (PSCs) are the inherent susceptibility of Sn²⁺ oxidation and the significant energy mismatch between the perovskite and electron transport layer (ETL). Doping of n-type polymer (N2200) into PCBM retards the Sn²⁺ oxidation and reduces the conduction band offset energy at the perovskite/ETL interface. This makes Sn-PSCs highly stable under operational conditions.

Abstract

Developing high-performance and stable Sn-based perovskite solar cells (PSCs) is difficult due to the inherent tendency of Sn²⁺ oxidation and, the huge energy mismatch between perovskite and Phenyl-C61-butyric acid methyl ester (PCBM), a frequently employed electron transport layer (ETL). This study demonstrates that perovskite surface defects can be passivated and PCBM's electrical properties improved by doping n-type polymer N2200 into PCBM. The doping of PCBM with N2200 results in enhanced band alignment and improved electrical properties of PCBM. The presence of electron-donating atoms such as S, and O in N2200, effectively coordinates with free Sn²⁺ to prevent further oxidation. The doping of PCBM with N2200 offers a reduced conduction band offset (from 0.38 to 0.21 eV) at the interface between the ETL and perovskite. As a result, the N2200 doped PCBM-based PSCs show an enhanced open circuit voltage of 0.79 V with impressive power conversion efficiency (PCE) of 12.98% (certified PCE 11.95%). Significantly, the N2200 doped PCBM-based PSCs exhibited exceptional stability and retained above 90% of their initial PCE when subjected to continuous illumination at maximum power point tracking for 1000 h under one sun.

A novel D-π-A configured small-molecule donor DTICPF is developed, which exhibits strong and broad optical absorption, and deep highest occupied molecular orbital (HOMO) energy levels. Vacuum-deposited organic solar cells (OSCs) based on DTICPF: C₇₀ display power conversion efficiency (PCE) of 9.36% (certified 9.15%) with short-circuit current density (J _sc) up to 17.49 mA cm⁻², which is the highest J _sc reported so far for vacuum-deposited OSCs.

Abstract

The development of high-performance organic photovoltaic materials is of crucial importance for the commercialization of organic solar cells (OSCs). Herein, two structurally simple donor-π-conjugated linker-acceptor (D-π-A)-configured small-molecule donors with methyl-substituted triphenylamine as D unit, 1,1-dicyanomethylene-3-indanone as A unit, and thiophene or furan as π-conjugated linker, named DTICPT and DTICPF, are developed. DTICPT and DTICPF are facilely prepared via a two-step synthetic process with simple procedures. DTICPF with a furan π-conjugated linker exhibits stronger and broader optical absorption, deeper highest occupied molecular orbital (HOMO) energy levels, and better charge transport, compared to its thiophene analog DTICPT. As a result, vacuum-deposited OSCs based on DTICPF: C₇₀ show an impressive power conversion efficiency (PCE) of 9.36% (certified 9.15%) with short-circuit current density (J _sc) up to 17.49 mA cm⁻² (certified 17.56 mA cm⁻²), which is the highest J _sc reported so far for vacuum-deposited OSCs. Besides, devices based on DTICPT: C₇₀ and DTICPF: C₇₀ exhibit excellent long-term stability under different aging conditions. This work offers important insights into the rational design of D-π-A configured small-molecule donors for high efficient and stable vacuum-deposited OSCs.

The different groups of amidino additives can largely impact defect passivation and crystallization dynamics of FAPbI₃ perovskite. Compared with ABAc containing carboxyl group, ABAm with amide group at para-position of amidino possesses large dipole and enables stronger interactions with perovskite components to produce high-quality perovskite film, delivering the higher efficiency of 24.60% and better long-term stability in ambient condition.

Abstract

Amidino-based additives show great potential in high-performance perovskite solar cells (PSCs). However, the role of different functional groups in amidino-based additives have not been well elucidated. Herein, two multifunctional amidino additives 4-amidinobenzoic acid hydrochloride (ABAc) and 4-amidinobenzamide hydrochloride (ABAm) are employed to improve the film quality of formamidinium lead iodide (FAPbI₃) perovskites. Compared with ABAc, the amide group imparts ABAm with larger dipole moment and thus stronger interactions with the perovskite components, i.e., the hydrogen bonds between N…H and I⁻ anion and coordination bonds between C = O and Pb²⁺ cation. It strengthens the passivation effect of iodine vacancy defect and slows down the crystallization process of α-FAPbI₃, resulting in the significantly reduced non-radiative recombination, long carrier lifetime of 1.7 µs, uniformly large crystalline grains, and enhances hydrophobicity. Profiting from the improved film quality, the ABAm-treated PSC achieves a high efficiency of 24.60%, and maintains 93% of the initial efficiency after storage in ambient environment for 1200 hours. This work provides new insights for rational design of multifunctional additives regarding of defect passivation and crystallization control toward highly efficient and stable PSCs.

The poor stability of perovskite solar cells is still a fatal defect. MgO buffer layer prepared by LTALD resists the erosion of water vapor, inhibits the migration of metal ions and the decomposition products of perovskite, and finally improves the stability of the device. At the same time, it passivates the defects of Spiro, thus enhancing carrier transport efficiency and device performance.

Abstract

The performance of perovskite solar cells has been continuously improving. However, humidity stability has become a key problem that hinders its promotion in the process of commercialization. A buffer layer deposited by atomic layer deposition is a very helpful method to solve this problem. In this work, MgO film is deposited between Spiro-OMeTAD and electrode by low-temperature atomic layer deposition at 80 °C, which resists the erosion of water vapor, inhibits the migration of electrode metal ions and the decomposition products of perovskite, then finally improves the stability of the device. At the same time, the MgO buffer layer can passivate the defects of porous Spiro, thus enhancing carrier transport efficiency and device performance. The Cs_0.05(FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskite device with a MgO buffer layer has displayed PCE of 22.74%, also with a high V_oc of 1.223 V which is an excellent performance in devices with same perovskite component. Moreover, the device with a MgO buffer layer can maintain 80% of the initial efficiency after 7200 h of storage at 35% relative humidity under room temperature. This is a major achievement for humidity stability in the world, providing more ideas for further improving the stability of perovskite devices.

A dual additives-assisted layer-by-layer sequential deposition strategy is used to prepare D18/L8-BO organic solar cells. DIM regulates D18 crystallization and DIO promotes L8-BO diffusion into the D18 layer, forming a vertical composition distribution active layer with large donor/acceptor interpenetrated regions. The optimized PCE of 19.59% is achieved.

Abstract

The ideal vertical phase separation active layer morphology is crucial for the photoelectric conversion of organic solar cells. In this work, a layer-by-layer sequential deposition method is used to prepare D18/L8-BO-based organic solar cells and a dual additives strategy is adopted to construct the ideal active layer. Additive DIM regulates the crystallization of the D18 layer, and additive DIO induces L8-BO to diffuse into the interior of the D18 layer to form a vertical composition distribution with large donor/acceptor interpenetrated regions. The improvement of active layer induced by DIM and DIO dual additives promote exciton generation and dissociation, shorten charge transfer distance, and improve carrier dynamics. With improved charge transport performance and suppressed carrier recombination, the short-circuit current density and fill factor of the D18/L8-BO quasi-bulk heterojunction organic solar cells are improved simultaneously, and the power conversion efficiency is boosted significantly from 18.21% to 19.59%. Moreover, the improved photovoltaic performance is further verified in D18/Y6 and PM6/L8-BO-based organic solar cells, which implies the generalizability of the dual additive-assisted layer-by-layer -sequential deposition method.

A novel strategy of passivating 2D perovskite in 3D/2D heterojunction with a thin surface termination layer is proposed. It demonstrates that surface defects of 2D perovskite are terminated by the AMTD molecule through multi-site interaction, resulting in an impressive PCE of 25.09% and a high V _OC of 1.211 V processed in air, with significantly enhanced long-term illumination and storing stability.

Abstract

Bilayer 3D/2D heterojunction perovskite solar cells (PSCs) have attracted increasing interest due to great advantages of high power conversion efficiency (PCE) and ultrastability. Previous studies are mostly focused on addressing the issue of poor charge transport originated from the spacer cations or random phase distribution of 2D perovskite in 3D/2D heterojunction. However, the carrier recombination at the surface of 2D layer is often ignored. Herein, a novel strategy of passivating 2D perovskite in 3D/2D heterojunction with a thin surface termination layer (STL) is proposed. It demonstrates that surface defects of 2D perovskite are terminated by the molecule of 2-amino-5-mercapto-1,3,4-thiadiazole through multi-site interaction, leading to the significant suppression of non-radiative recombination and considerable improvement of hole transport with the well-aligned energy band simultaneously. As a result, the PSCs with the constructed 3D/2D/STL structure processed in air have achieved a champion PCE of 25.09% with high open-circuit voltage of 1.211 V (the voltage deficient of 0.349 V). The unencapsulated devices retain exceeding 90% of the initial PCE after storing in air for 1008 h or under illumination in N₂ for 504 h. This work opens up an important, but unnoticed topic of defect passivation of 2D perovskite for 3D/2D heterojunction PSCs.

A new carbazole-based halo (iodine)-functional small molecule (O1) is successfully synthesized and employed as a hole-transport material (HTM) in inverted perovskite solar cells. Compared to the reference O2 HTM without any halo-function, the strong interaction between O1 and perovskite, i.e., I···I^- halogen bonding, leads to a big increase by 114 mV in the open-circuit voltage of corresponding devices.

Abstract

Interfacial properties of a hole-transport material (HTM) and a perovskite layer are of high importance, which can influence the interfacial charge transfer dynamics as well as the growth of perovskite bulk crystals particularly in inverted structure. The halogen bonding (XB) has been recognized as a powerful functional group to be integrated with new small molecule HTMs. Herein, a carbazole-based halo (iodine)-functional HTM (O1), is synthesized for the first time, demonstrating a high hole mobility and suitable energy levels that align well with those of perovskites. The strong interaction between O1 and perovskite, i.e., I···I⁻, induces the formation of an ordered interlayer, which are verified by both theoretical and experimental studies. Compared to the reference HTM (O2) without any halo-function, the XB-induced interlayer effectively enhances the interfacial charge extraction efficiency, while significantly hindering the non-radiative charge recombination by reducing the surface traps upon the strong passivation effect. This is reflected as a big increase in the open-circuit voltage by up to 114 mV in the fabrication of inverted devices with the highest power conversion efficiency of 22.34%. Moreover, the ordered XB-driven interlayer at the interface of O1 and perovskite is mainly responsible for the extended lifespan under the operational conditions.

A molecular design strategy for the third component is proposed. Starting with the Y6 molecular framework, asymmetric non-fullerene acceptors (BTP-SA1, BTP-SA2, BTP-SA3) through end-group, side-chain, and halogenation modifications are created. The ternary device, D18/Y6:BTP-SA3, shows a synergistic improvement in V _OC, J _SC, and FF, resulting in a high PCE of 19.36%, showcasing tolerance to varying component ratios (10–50%).

Abstract

The ternary strategy proves effective for breakthroughs in organic photovoltaics (OPVs). Elevating three photovoltaic parameters synergistically, especially the proportion-insensitive third component, is crucial for efficient ternary devices. This work introduces a molecular design strategy by comprehensively analyzing asymmetric end groups, side-chain engineering, and halogenation to explore the outstanding optoelectronic properties of the proportion-insensitive third component in efficient ternary systems. Three asymmetric non-fullerene acceptors (BTP-SA1, BTP-SA2, and BTP-SA3) are synthesized based on the Y6 framework and incorporated as the third component into the D18:Y6 binary system. BTP-SA3, featuring asymmetric terminal (difluoro-indone and dichloride-cyanoindone terminal), with branched alkyl side chains, exhibited high open-circuit voltage (V _OC), balanced crystallinity and compatibility, achieving synergistic enhancements in V _OC (0.862 V), short circuit-current density (J _SC, 27.52 mA cm⁻²), fill fact (FF, 81.01%), and power convert efficiency (PCE, 19.19%). Device based on D18/Y6:BTP-SA3 (layer-by-layer processed) reached a high efficiency of 19.36%, demonstrating a high tolerance for BTP-SA3 (10–50%). This work provides novel insights into optimizing OPVs performances in multi-component systems and designing components with enhanced tolerance.

By adopting side-chain tailoring strategy, two polymer hole-transporting materials with high mobility and multisite passivation functions are developed for the buried-interface engineering of inverted quasi-2D Ruddlesden‒Popper perovskite solar cells (PSCs). Among which, PVCz-ThSMeTPA-based inverted quasi-2D PSCs achieve impressive power conversion efficiency of 22.37% along with excellent thermal and long-term stability.

Abstract

Although quasi-2D Ruddlesden‒Popper (RP) perovskite exhibits advantages in stability, their photovoltaic performance are still inferior to 3D counterparts. Optimizing the buried interface of RP perovskite and suppress energetic losses can be a promising approach for enhancing efficiency and stability of inverted quasi-2D RP perovskite solar cells (PSCs). Among which, constructing polymer hole-transporting materials (HTMs) with defect passivation functions is of great significance for buried-interface engineering of inverted quasi-2D RP PSCs. Herein, by employing side-chain tailoring strategy to extend the π-conjugation and regulate functionality of side-chain groups, target polymer HTMs (PVCz-ThSMeTPA and PVCz-ThOMeTPA) with high mobility and multisite passivation functions are achieved. The presence of more sulfur atom-containing groups in side-chain endows PVCz-ThSMeTPA with increased intra/intermolecular interaction, appropriate energy level, and enhanced buried interfacial interactions with quasi-2D RP perovskite. The hole mobility of PVCz-ThSMeTPA is up to 9.20 × 10⁻⁴ cm² V⁻¹ S⁻¹. Furthermore, PVCz-ThSMeTPA as multifunctional polymer HTM with multiple chemical anchor sites for buried-interface engineering of quasi-2D PSCs can enable effective charge extraction, defects passivation, and perovskite crystallization modulation. Eventually, the PVCz-ThSMeTPA-based inverted quasi-2D PSC achieves a champion power conversion efficiency of 22.37%, which represents one of the highest power conversion efficiencies reported to date for quasi-2D RP PSCs.

Sodium periodate is employed to enhance the crystallinity and increase the Ni³⁺/Ni²⁺ ratio of sputtered NiO _x thin films. This treatment improves SAM's anchoring capability on NiO _x , optimizes hole extraction at the interface, and minimizes phase separation in perovskite films. As a result, the study successfully fabricates perovskite/silicon tandem solar cells with an impressive power conversion efficiency of up to 30.48%.

Abstract

Sputtering nickel oxide (NiO _x ) is a production-line-compatible route for depositing hole transport layers (HTL) in perovskite/silicon tandem solar cells. However, this technique often results in films with low crystallinity and structural flaws, which can impair electronic conductivity. Additionally, the complex surface chemistry and inadequate Ni³⁺/Ni²⁺ ratio impede the effective binding of self-assembled monolayers (SAMs), affecting hole extraction at the perovskite/HTL interface. Herein, these issues are addressed using a recrystallization strategy by treating sputtered NiO _x thin films with sodium periodate (NaIO₄), an industrially available oxidant. This treatment improved crystallinity and increased the Ni³⁺/Ni²⁺ ratio, resulting in a higher content of nickel oxyhydroxide. These enhancements strengthened the SAM's anchoring capability on NiO _x and improved the hole extraction at the perovskite/HTL interface. Moreover, the NaIO₄ treatment facilitated Na⁺ diffusion within the perovskite layer and minimized phase separation, thus improving device stability. As a result, single-junction perovskite solar cells with a 1.68 eV bandgap achieve a power conversion efficiency (PCE) of 23.22% for an area of 0.12 cm². Perovskite/silicon tandem cells with an area of 1 cm² reached a PCE of 30.48%. Encapsulated tandem devices retained 95% of their initial PCE after 300 h of maximum power point tracking under 1-sun illumination at 25 °C.

Rubidium thiocyanate as additive is incorporated in 1.66 eV bandgap perovskites to regulate film crystallization, significantly reduced device hysteresis, non-radiative recombination, ion-migration, and phase segregation. The perovskite solar cell achieved state-of-art 1.3 V V _OC and 24.3% efficiency, with T₈₀ lifetime of 944 h under 1 sun/65°C. After integrating with flat silicon subcell, 30% efficiency is obtained for silicon/perovskite tandem device.

Abstract

Developing high-quality wide bandgap (WBG) perovskites with ≈1.7 eV bandgap (E _g) is critical to couple with silicon and create efficient silicon/perovskite tandem devices. The sufferings of large open-circuit voltage (V _OC) loss and unstable power output under operation continuously highlight the criticality to fully develop high-quality WBG perovskite films. In this study, rubidium and thiocyanate as additive regulators in WBG perovskites are incorporated, significantly reducing non-radiative recombination, ion-migration, and phase segregation. The optimized 1.66 eV E _g perovskite solar cells achieved state-of-art 1.3 V V _OC (0.36 V deficit), and delivered a stabilized power conversion efficiency of 24.3%, along with good device stability (20% degradation (T₈₀) after over 994 h of operation under 1 sun at ≈65°C). When integrated with a flat front side silicon cell, silicon/perovskite two-terminal tandem device (30% efficient) is obtained with a 1.97 V V _OC, and T₉₀ operational lifetime of more than 600 h at room temperature.

A conductive adhesive, named polyaniline (PANI) with strong adhesion and high conductivity, is used to construct an adhesive bridge between SAM and perovskite layers. The nitrogen-containing groups of PANI are harnessed to passivate the buried interface defects, and the π–π interactions between PANI and SAM molecules facilitate the charge transport to optimize the buried interface contact. The strategy enables the inverted perovskite solar cells an impressive power conversion efficiency of 25.59%.

Abstract

The effective utilization of self-assembled monolayers (SAMs) has indeed resulted in significant improvement in the power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs). However, the poor interface contact between self-assembled monolayer (SAM) and perovskite layers limits the further improvement of inverted PSCs. Herein, polyaniline is employed as a conductive adhesive, enabling interaction with the perovskite and simultaneous coupling with the SAM, to optimize the buried interface contact. Furthermore, the adhesive strategy is validated to alleviate residual tensile strain at the buried interface using the non-destructive back grazing-incidence wide-angle X-ray scattering (BGIWAXS) technique. As a result, the optimized inverted PSCs achieve a champion PCE of 25.59% with impressive stability by retaining 97.3% of its initial efficiency after 1200 h under ambient conditions and light-emitting diode illumination. The findings provide a facial adhesive bridging strategy to play more impressive functions in the SAM-based inverted PSCs.

The heterogeneous integration of wide-bandgap semiconductors (WBGs) and 2D materials is emerging as a promising way to address various challenges faced by WBGs. This review covers recent advancements in fabrication techniques, mechanisms, devices, and novel functionalities of WBG/2D heterostructures. Furthermore, the directions and perspectives are outlined for realizing practical applications in the near future.

Abstract

Wide-bandgap semiconductors (WBGs) are crucial building blocks of many modern electronic devices. However, there is significant room for improving the crystal quality, available choice of materials/heterostructures, scalability, and cost-effectiveness of WBGs. In this regard, utilizing layered 2D materials in conjunction with WBG is emerging as a promising solution. This review presents recent advancements in the integration of WBGs and 2D materials, including fabrication techniques, mechanisms, devices, and novel functionalities. The properties of various WBGs and 2D materials, their integration techniques including epitaxial and nonepitaxial growth methods as well as transfer techniques, along with their advantages and challenges, are discussed. Additionally, devices and applications based on the WBG/2D heterostructures are introduced. Distinctive advantages of merging 2D materials with WBGs are described in detail, along with perspectives on strategies to overcome current challenges and unlock the unexplored potential of WBG/2D heterostructures.

The electron delocalization effect is innovatively utilized to optimize the interaction between additives and PbI₂, ensuring the regulation of the crystallization process while effectively avoiding the negative effects caused by additive residual. This strategy further enhanced the device performance, achieving an impressive power conversion efficiency of 25.95 %.

Abstract

Achieving high-efficiency perovskite solar cells (PSCs) hinges on the precise control of the perovskite film crystallization process, often improved by the inclusion of additives. While dimethyl sulfoxide (DMSO) is traditionally used to manage this process, its removal from the films is problematic. In this work, methyl phenyl sulfoxide (MPSO) was employed instead of DMSO to slow the crystallization rate, as MPSO is more easily removed from the perovskite structure. The electron delocalization associated with the benzene ring in MPSO decreases the electron density around the oxygen atom in the sulfoxide group, thus reducing its interaction with PbI². This strategy not only sustains the formation of a crystallization-slowing intermediate phase but also simplifies the elimination of the additive. Consequently, the optimized PSCs achieved a leading power conversion efficiency (PCE) of 25.95 % along with exceptional stability. This strategy provides a novel method for fine-tuning perovskite crystallization to enhance the overall performance of photovoltaic devices.

We develop a downsizing strategy by combining a dynamic bowl-shaped core with smaller DPA groups to fabricate structurally compact HTMs. The unique structure of the HTMs facilitates intermolecular π–π interactions, efficient film formation, and charge transport, resulting in enhanced charge mobility and glass transition temperature. Consequently, the PSC employing the dopant-free HTM exhibits an impressive PCE of 24.01 % along with exceptional operational stability, retaining 96 % of its initial performance after 800 hours.

Abstract

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor-(DPA)₅ , characterized by a bowl-shaped core with symmetric five diphenylamine groups. Compared to already-known HTMs, the bowl-shaped and relatively compact structure of cor-(DPA)₅ facilitates intermolecular π–π interactions, promotes film formations, and enhances charge transport. Consequently, the cor-[DPA(2)]₅ HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro-OMeTAD and cor-OMePTPA, our newly synthesized cor-(DPA)₅ HTM is free from any ionic dopants. As a result, the dopant-free cor-[DPA(2)]₅ -based PSC demonstrates an impressive efficiency of 24.01 %, and exhibits outstanding operational stability. It retains 96 % after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Methylamine gas treatment (MATM) presents a promising approach for “healing” perovskite films. Compared to other techniques such as antisolvent method, MATM yields perovskite films with more uniform morphology and higher crystallinity, leading to the enhanced conversion efficiency of over 18% for large-area perovskite module devices. These highlights demonstrate the significant potential of MATM for future large-scale production of perovskite films.

Methylamine (MA⁰) gas treatment (MATM) is a process that involves the adsorption of MA⁰ on methylammonium (MA)-based lead perovskite thin films, forming an adsorption intermediate, which appears as a visually transparent liquid. When MA⁰ is desorbed from this intermediate, recrystallization of the MA-based perovskite occurs. Due to the highly reversible nature of MATM and its ability to inherently levelize the film surface through liquefaction, MATM is a promising method for fabricating uniform and intact perovskite thin films over large areas, which is crucial for the commercialization of perovskite solar cells. Herein, efforts to control the MATM process are presented, including slowing down the kinetics of MA adsorption by introducing a diluent into the MA stock solution, establishing a monitoring system to investigate the desorption process in detail, and demonstrating the success of MATM in fabricating perovskite solar modules. It is found that MATM not only heals morphological flaws but also promotes (110) orientation crystallinity and reduces trap density in recrystallized MAPbI₃ films. Finally, MATM is applied to prepare perovskite minimodules using an in-house designed MA-induced liquefaction and recrystallization reactor. The minimodule (5 × 5 cm) fabricated using MATM achieves 18.32% efficiency, significantly surpassing the performance of those fabricated using antisolvent-treating (7.50%) and vacuum drying (16.09%) methods.

A cross-linkable fullerene (BCM) is synthesized and used as an electron transport layer (ETL) in inverted perovskite solar cells (PSCs). BCM can in situ form a compact cross-linked BCM (CBCM) film that not only effectively transports electrons but also acts as an internal encapsulation layer to suppress the diffusion of perovskite components, thereby achieving high-efficiency and long-term stability in PSCs.

Abstract

A stable and compact fullerene electron transport layer (ETL) is crucial for high-performance inverted perovskite solar cells (PSCs). However, traditional fullerene-based ETLs like C₆₀ and PCBM are prone to aggregate under operational conditions, a challenge recently recognized by academic and industrial researchers. Here, we designed and synthesized a novel cross-linkable fullerene molecule, bis((3-methyloxetan-3-yl)methyl) malonate-C₆₀ monoadduct (BCM), for use as an ETL in PSCs. Upon a low-temperature annealing at 100 °C, BCM undergoes in situ cross-linking to form a robust cross-linked BCM (CBCM) film, which demonstrates excellent electron mobility and a suitable band structure for efficient PSCs. Our results show that PSCs incorporating CBCM-based ETL achieve an impressive efficiency of 25.89 % (certified: 25.36 %), significantly surpassing the 23.25 % efficiency of PCBM-based devices. The intramolecular covalent interactions within CBCM films effectively prevent aggregation and enhance film compactness, creating an internal encapsulation layer that mitigates the decomposition and ion migration of perovskite components. Consequently, CBCM-based PSCs show exceptional stability, maintaining 97.8 % of their initial efficiency after 1000 hours of maximum power point tracking, compared to only 78.6 % retention in PCBM-based devices after less than 820 hours.

Nature Energy, Published online: 18 October 2024; doi:10.1038/s41560-024-01651-2

This work introduces a reactive passivator at the perovskite/C₆₀ interface to suppress non-radiative recombination and enhance charge carrier transport across the interface. The tailored perovskite/C₆₀ interface improves the performance of perovskite/silicon tandem solar cells, resulting in a stabilized efficiency of 30.59%. The unencapsulated device retains 94% of its initial efficiency over 200 h under continuous 1-sun full spectrum illumination.

Abstract

Integrating perovskite solar cells with crystalline silicon bottom cells in a monolithic two-terminal tandem configuration enables power conversion efficiency (PCE) surpassing the theoretical limits of single-junction cells. However, wide bandgap (WBG) perovskite films face challenges related to phase stability and open circuit voltage (V _OC) deficit, particularly due to severe non-radiative recombination at the perovskite/C₆₀ interface. Here, the interfacial defects are passivated by incorporating a reactive passivator that reacts with lead halides to form low-dimensional phases. The target product obtained by optimizing the reaction temperature not only suppresses recombination across the interface, but also facilitates the transfer of charge carriers. More importantly, this product can suppress phase segregation of WBG perovskite films under exposure to light illumination and moisture. This strategy enables a high V _OC of 1.25 V for WBG perovskite device based on polymer hole transport layer and a certified stabilized PCE of 30.52% for a monolithic perovskite/silicon tandem solar cell. The unencapsulated tandem device retains 94% of its initial PCE over 200 h under continuous 1-sun full spectrum illumination in air, demonstrating the improved phase stability.

Thiophene-based cations are introduced in tin halide perovskites to form 2D/3D heterojunctions, in which 2-(thiophen-3-yl)ethan-1-aminium (3-TEA) leads to the most compact crystal packing of [SnI₆]⁴⁻ octahedral layers with the lowest hole effective mass and formation energy in the resultant 2D phase. This effect facilitates charge transfer in the tin-based perovskite solar cells and improves the device efficiency and stability.

Abstract

Tin halide perovskites are the most promising candidate materials for lead-free perovskite solar cells (PSCs) thanks to their low toxicity and ideal band gap energies. The introduction of 2D/3D mixed perovskite phases in tin-based PSCs (TPSCs) has proven to be the most effective approach to improving device efficiency and stability. However, a 2D perovskite phase normally shows relatively low carrier mobility, which will be unfavorable for carrier transfer in the devices. In this work, we used a thiophene-based cation 2-(thiophen-3-yl)ethan-1-aminium (3-TEA) as a spacer to form a novel 2D perovskite phase in TPSCs, which shows the most promising effect on the performance enhancement in comparison with other cations like 2-(thiophen-2-yl)ethan-1-aminium (2-TEA) and benzene-based 2-phenylethan-1-aminium (PEA). Theoretical calculations reveal that 3-TEA enables the most compact crystal packing of [SnI₆]⁴⁻ octahedral layers, resulting in the lowest hole effective mass and formation energy in the 2D phase. This effect significantly enhances device efficiency and stability by facilitating more efficient carrier transfer within the 2D phase. These findings indicate that thiophene-based 2D perovskites are well-suited for high-performance TPSCs.

An integrated omnidirectional strategy for designing non-volatile solid additives was proposed, by employing this strategy, new solid additive PyMC5 was designed. Compared with its counterpart PyDC5, PyMC5 is capable of enhancing the photo-/thermal-stability of the device and boosting the power conversion efficiency of the binary OSC to 19.52 %, this result is among the best efficiencies reported so far.

Abstract

Solid additives have drawn great attention due to their numerous appealing benefits in enhancing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). To date, various strategies have been reported for the selection or design of non-volatile solid additives. However, the lack of a general design/evaluation principles for developing non-volatile solid additives often results in individual solid additives offering only one or two efficiency-boosting attributes. In this work, we propose an integrated omnidirectional strategy for designing non-volatile solid additives. By validating the method on the 4,5,9,10-pyrene diimide (PyDI) system, a novel non-volatile solid additive named PyMC5 was designed. PyMC5 is capable of enhancing device performance by establishing synergistic dual charge transfer channels, forming appropriate interactions with active layer materials, reducing non-radiative voltage loss and optimizing film morphology. Notably, the binary device (PM6 : L8-BO) treated by PyMC5 achieved a PCE over 19.5 %, ranking among the highest reported to date. In addition, the integration of PyMC5 mitigated the degradation process of the devices under photo- and thermal-stress conditions. This work demonstrates an efficient integrated omnidirectional approach for designing non-volatile solid additives, offering a promising avenue for further advancements in OSC development.

We developed a new electron-deficient arene, fluorinated bithiophene imide (F-BTI) and its polymer donor SA1, in which two fluorine atoms were introduced at the β-positions in the thiophene rings of BTI to fine-tune the energy levels and aggregation of the resulting polymers. The SA1-based all-PSCs achieved a record efficiency of 19.33 % (certified PCE: 19.17 %). These results highlight that F-BTI is a promising unit for constructing high-performance polymer donors for all-PSCs.

Abstract

All-polymer solar cells (all-PSCs) present compelling advantages for commercial applications, including mechanical durability and optical and thermal stability. However, progress in developing high-performance polymer donors has trailed behind the emergence of excellent polymer acceptors. In this study, we report a new electron-deficient arene, fluorinated bithiophene imide (F-BTI) and its polymer donor SA1, in which two fluorine atoms are introduced at the outer β-positions in the thiophene rings of BTI to fine-tune the energy levels and aggregation of the resulting polymers. SA1 exhibits a deep HOMO level of −5.51 eV, a wide bandgap of 1.81 eV and suitable miscibility with the polymer acceptor. Polymer chains incorporating F-BTI result in a highly ordered π–π stacking and favorable phase-separated morphology within the all-polymer active layer. Thus, SA1 : PY-IT-based all-PSCs exhibit an efficiency of 16.31 % with excellent stability, which is further enhanced to a record value of 19.33 % (certified: 19.17 %) by constructing ternary device. This work demonstrates that F-BTI offers an effective route for developing new polymer materials with improved optoelectronic properties, and the emergence of F-BTI will change the scenario in terms of developing polymer donor for high-performance and stable all-PSCs.

A series of π-conjugated polymers based on thienobenzobisthiazole (TBTz) with alkyl, ester, and acyl groups are synthesized by the late-stage functionalization strategy, where the TBTz-monomers are efficiently synthesized via the common intermediate. Among them, the ester-functionalized polymer shows the highest power conversion efficiency in organic photovoltaic cells with a small nonradiative voltage loss and a high charge generation efficiency.

Abstract

Derivatization is essential for optimizing organic material properties. However, because functional groups are often introduced at an early stage of the synthesis, similar intermediates have to be repeatedly synthesized to produce derivatives, which amounts to a daunting and time-consuming task. Using thienobenzobisthiazole (TBTz) as a building unit of donor polymers for organic photovoltaics (OPVs), we demonstrate an efficient derivatization of a TBTz-based π-conjugated polymer by late-stage functionalization. In the developed synthetic route, functional groups are introduced at the last step of monomer synthesis, enabling us to easily synthesize several derivatives from a common intermediate. Ester and acyl groups are introduced into the polymer instead of the alkyl group, giving rise to deep HOMO energy levels and resulting in OPV cells with high open-circuit voltage even in the absence of halogen substituents that are typically introduced into the donor polymers. Notably, the ester-functionalized TBTz-based polymer shows a small nonradiative voltage loss (ΔV _nr) of 0.19 V and has one of the highest charge generation efficiencies among the halogen-free donor polymers with similar ΔV _nr, improving the critical trade-off relationship between voltage loss and charge generation. Our results provide an important guideline for the efficient development of high-performance polymers for OPVs.