Chen Weijie

A series of non-fullerene acceptors (NFAs, Y-H, Y-F, and Y-Cl) are introduced as modifier layers for perovskite/electron transport layers (ETL) interface, causing a decrease in non-radiative recombination. Furthermore, profiting from the cascade energy-level alignment and superior carrier transport, the inverted perovskite solar cell achieves an impressive power conversion efficiency of 24.52%.

Abstract

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 FA_0.88Cs_0.12PbI_2.64Br_0.36 (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 Cs_0.05(FA_0.95MA_0.05)_0.95PbI_2.64Br_0.36 (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.

Multi-carboxylate potassium salts are performed to bridge SnO₂ and perovskite. The mechanisms of hysteresis elimination and buried interface bridging are revealed. The bridging interaction is dominated by carboxyl groups, potassium ions, and molecular twist. The formation of K-I₄ chemical bonds immobilizes the surface of iodine, enhancing iodine mobility energy. Bridging molecules with good twisting ability facilitate COO-Sn, COO-Pb, and K-I₄ coordination.

Abstract

Interface passivation through Lewis acid–base coordinate chemistry in perovskite solar cells (PSCs) is a universal strategy to reduce interface defects and hinder ion migration. However, the formation of coordinate covalent bonding demands strict directional alignment of coordinating atoms. Undoubtedly, this limits the selected range of the interface passivation molecules, because a successful molecular bridge between charge transport layer and perovskite bottom interface needs a well-placed molecular orientation. In this study, it is discovered that potassium ions can migrate to the hollow sites of multiple iodine ions from perovskite to form K-I_x ionic bonding, and the ionic bonds without directionality can support molecular backbone rotation to facilitate polar sites (carboxyl groups) chelating Pb at the bottom perovskite interface, finally forming a closed-loop bonding structure. The synergy of coordinate and ionic bonding significantly reduces interface defects, changes electric field distribution, and immobilizes iodine at the perovskite bottom interface, resulting in eliminating the hysteresis effect and enhancing the performance of PSCs. As a result, the corresponding devices achieve a high efficiency exceeding 24.5% (0.09 cm²), and a mini-module with 21% efficiency (12.4 cm²). These findings provide guidelines for designing molecular bridging strategies at the buried interface of PSCs.

A novel aluminum halide-based electron-selective passivating contact for crystalline silicon solar cells is reported. By the implementation of ultrathin silicon oxide passivation interlayer and thermally evaporated electron-selective aluminum fluoride thin film, a silicon solar cell with an efficiency of 21% is achieved. This work expands the pool of available metal compound-based passivating contacts for crystalline silicon solar cells.

Abstract

Extensive research has focused on developing wide-bandgap metal compound-based passivating contacts as alternatives to conventional doped-silicon-layer-based passivating contacts to mitigate parasitic absorption losses in crystalline silicon (c-Si) solar cells. Herein, thermally-evaporated aluminum halides (AlX)-based electron-selective passivating contacts for c-Si solar cells are investigated. A low contact resistivity of 60.5 and 38.4 mΩ cm² is obtained on the AlCl _x /n-type c-Si (n-Si) and AlF _x /n-Si heterocontacts, respectively, thanks to the low work function of AlX. Power conversion efficiencies (PCEs) of 19.1% and 19.6% are achieved on proof-of-concept n-Si solar cells featuring a full-area AlCl _x /Al and AlF _x /Al passivating contact, respectively. By further implementing an ultrathin SiO₂ passivation interlayer and a pre-annealing treatment, the electron selectivity (especially the surface passivation) of AlX is significantly enhanced. Accordingly, a remarkable PCE of 21% is achieved on n-Si solar cells featuring a full-area SiO₂/AlF _x /Al rear contact. AlF _x -based electron-selective passivating contacts exhibit good thermal stability up to ≈400 °C and better long-term environmental stability. This work demonstrates the potential of AlF _x -based electron-selective passivating contact for solar cells.

An unprecedented triple cross-linking engineering strategy is proposed by introducing cross-linkable 4-fluorophenyl 5-(1,2-dithiolan-3-yl) pentanoate into the bottom, bulk, and top interface of the perovskite film to form steric passivation, enabling flexible perovskite solar cells with excellent PCE and superior overall stability.

Abstract

Inverted flexible perovskite solar cells (fPSCs) are promising for commercialization due to their low cost, lightweight, and excellent stability. However, enhancing fPSCs’ power conversion efficiency and stability remains challenging. Here, an unprecedented triple cross-linking engineering strategy is innovatively exhibit for efficient and stable inverted fPSCs. First, a carefully designed cross-linker, 4-fluorophenyl 5-(1,2-dithiolan-3-yl) pentanoate (FB-TA), is added to the perovskite precursor solution. During the perovskite film's crystallization at a low temperature, the cross-linking product of FB-TA can passivate the grain boundaries and reduce the film's residual strain and Young's module. Then, FB-TA is also introduced for the bottom- and top-interface modification of the perovskite film. The interfacial treating strategy protects the perovskite from water invasion and strengthens the interfaces. The combination of triple strategies affords highly efficient inverted fPSCs with a champion efficiency of 21.42% among the state-of-the-art inverted fPSCs based on nickel oxides. More importantly, the flexible devices also exhibit superior stabilities with T₉₀ >4000 bending cycles, photostability with T₉₀ >568 h, and ambient stability with T₉₀ >2000 h, especially the stability with T₈₀ >1120 h under harsh damp-heat conditions (i.e., 85 °C and 85% RH). The strategy provides new insights into the industrialization of high-performance and stable fPSCs.

In this study, enhanced particle-to-particle interaction is demonstrated in the electron-transport layer ink by a phase-transfer catalyst, resulting in the highest efficiency (17.6%) for all scalable flexible n–i–p-structured perovskite solar cells based on MAPbI₃ fabricated in ambient air using scalable techniques.

Perovskite solar cells (PSCs) have exceeded 26% efficiency. One attribute of PSCs is their printability at relatively low temperatures, particularly advantageous for flexible solar cells. However, developing efficient, fully printable flexible PSCs on rough and soft plastic substrates remains a challenge. Herein, efficient flexible PSCs fabricated by only scalable methods in ambient conditions are reported. First, the source of the issue in fabricating flexible PSCs—the presence of charge carrier shorting pathways within electron-transport layer (ETL) due to incomplete coverage of surface of flexible substrates—is identified. To address this challenge, the ETL deposition ink is modified with a phase-transfer catalyst, often used in synthetic organic chemistry. Dynamic light scattering and nuclear-magnetic resonance studies show that the catalyst enhances ETL particle-to-particle interaction in the ink, eventually leading to conformal coverage of rough flexible substrates. As a result, a power conversion efficiency of 17.6% for all-scalable flexible n–i–p-structured PSCs based on methylammonium lead iodide (MAPbI₃) is demonstrated, among the highest reported to date for fully scalable flexible PSCs, all fabricated in ambient air.

Incorporating trisodium citrate (TC) into SnO₂ precursor efficiently inhibits SnO₂ nanoparticle agglomeration, eliminating defects and reducing surface work function of electron-transport layer. Additionally, enhanced interface interaction improves the stability of perovskite layer, resulting in a reduction in lead leakage. Finally, the modification with TC enhances the performance and stability of the fully air-processed perovskite solar cells.

Electron-transport layer (ETL) is integral in conventional perovskite solar cells (PSCs), serving as an essential role in both the growth of perovskite and the extraction of charge carriers. This dual functionality poses a challenge, especially in the context of the ETL in all-air-processed PSCs. Herein, a multifunctional modification strategy is proposed, where trisodium citrate (TC) is incorporated into SnO₂ precursor. The introduction of TC can efficiently inhibit the agglomeration of SnO₂ nanoparticle in precursor. This also eliminates the oxygen vacancy defects and reduces the work function of the SnO₂ film surface. This synergistic effect remarkably improves the quality of ETL. Meanwhile, TC can passivate the undercoordinated Pb²⁺ at the buried interface, thus suppressing nonradiative recombination and reducing lead leakage. Furthermore, Na ions in the TC molecule facilitate the perovskite crystallization by migrating into the perovskite layer, resulting in formation of a high-quality perovskite film. Consequently, the efficiency of the TC-treated device made in fully ambient-air conditions reaches 21.17% with suppressing hysteresis. In particular, the unencapsulated device maintains about 81% of the original efficiency after 2500 h under air exposure. In this study, a straightforward and effective method is presented for achieving efficient and stable air-processed PSCs.

Post-treatment of the Sn–Pb perovskite films with phenylhydrazine effectively reduces hole trap density, which leads to an increase in power conversion efficiency from 18.16% to 20.67% due mainly to the significant improvement of open-circuit voltage from 0.75 to 0.83 V.

Narrow-bandgap Sn–Pb-alloyed perovskite is potential for a bottom cell in perovskite tandem solar cells. However, Sn-contained perovskites tend to be readily oxidized in air atmosphere, which has ill influence on stability and photovoltaic performance. Herein, a method to suppress oxidation of divalent tin via post-treatment of perovskite film with phenylhydrazine is reported. Phenylhydrazine-treated FA_0.5MA_0.5Pb_0.5Sn_0.5I₃ perovskite films effectively reduce the hole traps caused by the oxidation of Sn²⁺ on the perovskite surfaces. In addition, surface energetics are well aligned by post-treatment, which is beneficial for voltage gain and charge transport. As a result, power conversion efficiency (PCE) is increased from 18.16% to 20.67% after post-treatment due mainly to the significant improvement of open-circuit voltage from 0.75 to 0.83 V. Furthermore, the device stability is improved, where 91.67% of initial PCE is maintained after 1000 h.

Differing from the previous fluorinated photovoltaic materials that C(sp²)─F bonds in conjugated backbone or C(sp³)─F bonds in sidechains, this work develops a new molecular design concept by introducing polyfluoride units containing C(sp³)─F bonds into the backbone, which would not affect the conjugation but enhance the intermolecular interaction. Thus, the relevant fluoropolymers exhibit superior performance in the ternary organic solar cells.

Abstract

Fluorination strategy is demonstrated to be a successful approach for optimizing the electron distribution and morphology of organic photovoltaic materials. The previous works focus on introducing only a few C(sp²)─F bonds into conjugated backbone or C(sp³)─F bonds into sidechains. Herein, a new strategy by introducing C(sp³)─F polyfluoride unit into the backbone is proposed, wherein the fluorine atoms are not involved into the conjugation but can promote the intermolecular interaction between backbones. Two wide-bandgap fluoropolymers are prepared and employed as the third component for ternary organic solar cells. As expected, even if there are six fluorine atoms in a single repeat unit, the relevant fluoropolymers possess complementary absorption and aligned energy levels. More importantly, the polyfluoride backbone affords adequate non-covalent interactions, consequently enhancing the polymer aggregation and packing order, which is verified by a fibril-like morphology in the blend film with the host polymer PM6 and only 10 wt.% fluoropolymer. In addition, the decreased surface energy caused by polyfluoride unit is beneficial for the improvement of domain purity and the formation of nanoscale phase separation between donor and acceptor materials. As a result, the fluoropolymer-assisted ternary device displays a higher efficiency of 18.74% compared with the binary device (17.39%).

The research utilizing guanidine phosphate in perovskite films creates a low-dimensional perovskite enveloping layer at the buried interface and grain boundaries, enhancing exciton dissociation, and reducing recombination while improving moisture resistance. This approach results in an improved power conversion efficiency and a T90 lifetime of 1000 h under MPPT tests, marking an advancement in perovskite solar energy technology.

Abstract

To elevate the performance and durability of perovskite solar cells, a holistic approach to mitigating defects throughout the device is essential. While advancements in refining top interfaces have been significant, the potential of stabilizing buried interfaces and grain boundaries has not been fully tapped. The research underscores the transformative impact of guanidine phosphate (GP), a chemical agent that converts surplus PbI₂ into a low-dimensional perovskite, thus reinforcing the stability of both buried interfaces and grain boundaries. Employing GP on quantum dot tin dioxide (QD-SnO₂) surfaces revealed an exceptional grain wrapping effect at these critical junctures, as revealed by high-resolution transmission electron microscopy. This novel low-dimensional perovskite enveloping strategy not only passivates the grain boundaries but also delays the cooling of hot carriers, thereby diminishing charge carrier recombination. This strategy exhibits an enhanced power conversion efficiency, rising from 23.16% to 24.55%. Moreover, the modified device sustains over 90% of their initial efficiency after 1000 h of maximum power point tracking under one sun illumination and maintain 90% efficiency after 1400 h in moderate humidity, all achieved without the encapsulation. This breakthrough points to a robust method for augmenting perovskite solar cell, promising a more durable, and efficient solar energy.

This work sandwiches Cd-CsPbCl₃:Mn²⁺ QDs within the gaps of ETLs to prevent their diffusion into the perovskite. Moreover, this work adopts the method of dual fluorescence conversion layers inside and outside the PSCs with the PCE of 24.63% with significantly improved photostability. This work paves the way for the development of efficient and stable photoluminescence-converted PSCs.

Abstract

Introduction of fluorescent down-conversion layer inside perovskite solar cells (PSCs) can highly improve the ultraviolet response of the devices and the light stability. However, such a device is usually confronted with the problem of inter-diffusion with the perovskite absorber layer, which severely limits its further development. To address this problem, herein, this work employs an interfacial dual electron transport layers (ETLs) strategy, sandwiching Cd-CsPbCl₃:Mn²⁺ luminescent quantum dots within gap of the ETLs, which not only reduces the interface energy level offset, but also improves the nucleation and crystallization kinetics of perovskite films and prevents their diffusion to the perovskite absorber layer. As a result, the efficient synergy effect effectively elevates both the open-circuit voltage and fill factor of the PSCs, reaching maximum values of 1.181 V and 81.14%, respectively, finally delivering progressively increased device power conversion efficiency (PCE) of 24.32% with significantly improved light stability. To further improve the ultraviolet response, this work further adopts the strategy of dual fluorescent conversion layers inside and outside the PSCs, and finally obtains PCE of 24.63%, which is the best for various luminescent conversion cells. This work opens a new door for the development of efficient and stable photoluminescence conversion PSCs.

Charge transport plays a significant role in determining the performance of organic solar cells (OSCs). Here, a highly interconnected electron-transport pathway in simple-structured nonfused-ring electron acceptor (NFREA) is achieved by manipulating the alkyl-chain topology. Therefore, the 3TTB-4F with branched alkyl side-chains demonstrates a record-breaking power conversion efficiency of 17.38% (certified 16.59%), establishing it as the highest efficiency among NFREA-based OSCs.

Abstract

Achieving desirable charge-transport highway is of vital importance for high-performance organic solar cells (OSCs). Here, it is shown how molecular packing arrangements can be regulated via tuning the alkyl-chain topology, thus resulting in a 3D network stacking and highly interconnected pathway for electron transport in a simple-structured nonfused-ring electron acceptor (NFREA) with branched alkyl side-chains. As a result, a record-breaking power conversion efficiency of 17.38% (certificated 16.59%) is achieved for NFREA-based devices, thus providing an opportunity for constructing low-cost and high-efficiency OSCs.

This review systematically summarizes asymmetric small-molecule acceptors and donors, exploring their structure-performance relationship, molecular packing, and morphology. Balancing open circuit voltage and short-circuit current density, reducing charge recombination and non-radiative recombination are crucial for enhancing photovoltaic performance in asymmetric materials. Finally, challenges and prospects for future development and application of asymmetric molecules and asymmetric strategies are discussed.

Abstract

The conjugated small-molecule materials of organic solar cells have always played a crucial role in light-harvesting, charge transport, morphology optimization, and the attainment of efficient devices. The advancement of novel materials and the understanding of underlying molecular design rules serve as the driving force for furthering efficient and stable photovoltaic devices. Among a variety of design principles, the symmetry-breaking strategy, which is well developed in 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene (ITIC)-series acceptors, recently demonstrates great potential in small-molecule acceptors and donors for realizing high power conversion efficiency. In this review, in order to give a deep insight on asymmetric strategy, the small-molecule acceptors and donors are systematically summarized with asymmetric structure to elucidate structure-performance relationship, molecular packing behaviors, and morphology evolution. Not only the delicate balance between open circuit voltage and short-circuit current density, but also the reductions in charge recombination and non-radiative recombination are considered to play the key points in improving the photovoltaic performance when the asymmetric molecule is used as host or guest materials. Finally, concise challenges and outlooks are provided for the future development and application of asymmetric molecules and symmetry-breaking strategies.

A cyclic reaction pathway in perovskite conversion facilitated by catalytic PbI₂-mesylate anion complexes is explored. This approach yields a remarkably homogeneous perovskite film, resulting in a remarkable power conversion efficiency of 24.51% and excellent maximum-power-point-tracking stability in the corresponding perovskite solar cells.

Abstract

High-quality perovskite films are essential for achieving high performance of optoelectronic devices; However, solution-processed perovskite films are known to suffer from compositional and structural inhomogeneity due to lack of systematic control over the kinetics during the formation. Here, the microscopic homogeneity of perovskite films is successfully enhanced by modulating the conversion reaction kinetics using a catalyst-like system generated by a foaming agent. The chemical and structural evolution during this catalytic conversion is revealed by a multimodal synchrotron toolkit with spatial resolutions spanning many length scales. Combining these insights with computational investigations, a cyclic conversion pathway model is developed that yields exceptional perovskite homogeneity due to enhanced conversion, having a power conversion efficiency of 24.51% for photovoltaic devices. This work establishes a systematic link between processing of precursor and homogeneity of the perovskite films.

An interface bridging strategy (IBS) is proposed to mitigate energy loss and enhance stability at the perovskite/C₆₀ interface by designing A-D-A type perylene monoimide (PMI) derivatives. This IBS effectively passivates surface defects, enhances interfacial coupling, and optimizes the film-forming process of the C₆₀ layer, leading to the successful development of large-area, high-performance perovskite solar submodules with an efficiency of 18.7%.

Abstract

As the photovoltaic field endeavors to transition perovskite solar cells (PSCs) to industrial applications, inverted PSCs, which incorporate fullerene as electron transport layers, have emerged as a compelling choice due to their augmented stability and cost-effectiveness. However, these attributes suffer from performance issues stemming from suboptimal electrical characteristics at the perovskite/fullerene interface. To surmount these hurdles, an interface bridging strategy (IBS) is proposed to attenuate the interface energy loss and enhance the interfacial stability by designing a series of A-D-A type perylene monoimide (PMI) derivatives with multifaceted advantages. In addition to passivating defects, the IBS plays a crucial role in facilitating the binding between perovskite and fullerene, thereby enhancing interface coupling and importantly, improving the formation of fullerene films. The PMI derivatives, functioning as bridges, serve as a protective barrier to enhance the device stability. Consequently, the IBS enables a remarkable efficiency of 24.62% for lab-scale PSCs and an efficiency of 18.73% for perovskite solar modules craft on 156 × 156 mm² substrates. The obtained efficiencies represent some of the highest recorded for fullerene-based devices, showcasing significant progress in designing interfacial molecules at the perovskite/fullerene interface and offering a promising path to enhance the commercial viability of PSCs.

Publication date: 17 April 2024

Source: Joule, Volume 8, Issue 4

Author(s): Yaohua Wang, Yuanyuan Meng, Chang Liu, Ruikun Cao, Bin Han, Lisha Xie, Ruijia Tian, Xiaoyi Lu, Zhenhua Song, Jun Li, Shuncheng Yang, Congda Lu, Ziyi Ge

Three new non-fully conjugated dimerized giant acceptors with different alkyl-linked sites are developed. Among them, wing-sited 2Y-wing has fine-tuned packing and better miscibility with donor, allowing to 19.13 % efficiency (which is the highest value among the devices with giant acceptors) and highly stable organic solar cells.

Abstract

Achieving both high power conversion efficiency (PCE) and device stability is a major challenge for the practical development of organic solar cells (OSCs). Herein, three non-fully conjugated dimerized giant acceptors (named 2Y-sites, including wing-site-linked 2Y-wing, core-site-linked 2Y-core, and end-site-linked 2Y-end) are developed. They share the similar monomer precursors but have different alkyl-linked sites, offering the fine-tuned molecular absorption, packing, glass transition temperature, and carrier mobility. Among their binary active layers, D18/2Y-wing has better miscibility, leading to optimized morphology and more efficient charge transfer compared to D18/2Y-core and D18/2Y-end. Therefore, the D18/2Y-wing-based OSCs achieve a superior PCE of 17.73 %, attributed to enhanced photocurrent and fill factor. Furthermore, the D18/2Y-wing-based OSCs exhibit a balance of high PCE and improved stability, distinguishing them within the 2Y-sites. Building on the success of 2Y-wing in binary systems, we extend its application to ternary OSCs by pairing it with the near-infrared absorbing D18/BS3TSe-4F host. Thanks to the complementary absorption within 300–970 nm and further optimized morphology, ternary OSCs obtain a higher PCE of 19.13 %, setting a new efficiency benchmark for the dimer-derived OSCs. This approach of alkyl-linked site engineering for constructing dimerized giant acceptors presents a promising pathway to improve both PCE and stability of OSCs.

Amine-releasable mediator methylammonium pyridine-2-carboxylic (MAPyA) is demonstrated to in situ repair the imperfections in perovskite film. The specific mechanism is that MAPyA-released methylamine gifts a crystal reconstruction environment by inducing liquid intermediate phase, thus reconvert the microcrystals and residual PbI₂ to perfect perovskites in situ. The optimized device exhibits efficiency of 24.06 % and excellent photostability.

Abstract

Residual lead iodide (PbI₂) is deemed to a double-edged sword in perovskite film as small amounts of PbI₂ are beneficial to the photovoltaic performance, but excessive will cause degradation of photovoltaic performance and stability. Herein, an in situ repair strategy has been developed by introducing amine-releasable mediator (methylammonium pyridine-2-carboxylic, MAPyA) to eliminate over-residual PbI₂ and regulate the crystal quality of perovskite film. Notably, MAPyA can be partially decomposed into methylamine (MA) gas and pyridine-2-carboxylic (PyA) during high temperature annealing. The released MA can locally form liquid intermediate phase, facilitating the reconstruction of perovskite microcrystals and residual PbI₂. Moreover, the leftover PyA is confirmed to effectively passivate the uncoordinated lead ions in final perovskite film. Based upon this, superior perovskite film with optimized crystal structure and holistic negligible PbI₂ is acquired. The assembled device realizes outstanding efficiency of 24.06 %, and exhibits a remarkable operational stability that maintaining 87 % of its origin efficiency after continuous illumination for 1480 h. And the unencapsulated MAPyA-treated devices present significant uplift in humidity stability (maintaining ~93 % of the initial efficiency over 1500 h, 50–60 % relative humidity). Furthermore, the further optimization of this strategy with nanoimprint technology proves its superiority in the amplificative preparation for perovskite films.

PTFBK has been employed as a multifunctional additive to target and modulate bulk perovskite defects and carrier dynamics of PSCs, endowing the decrease of Young′s modulus and residual stress in the perovskite layer. Moreover, benefit to the dominant crystal orientation and the suppression of non-radiative recombination, excellent stable inverted device with PCE of 24.99% was achieved.

Abstract

The main obstacles to promoting the commercialization of perovskite solar cells (PSCs) include their record power conversion efficiency (PCE), which still remains below the Shockley–Queisser limit, and poor long-term stability, attributable to crystallographic defects in perovskite films and open-circuit voltage (V _oc) loss in devices. In this study, potassium (4-tert-butoxycarbonylpiperazin-1-yl) methyl trifluoroborate (PTFBK) was employed as a multifunctional additive to target and modulate bulk perovskite defects and carrier dynamics of PSCs. Apart from simultaneously passivating anionic and cationic defects, PTFBK could also optimize the energy-level alignment of devices and weaken the interaction between carriers and longitudinal optical phonons, resulting in a carrier lifetime of greater than 3 μs. Furthermore, it inhibited non-radiative recombination and improved the crystallization capacity in the target perovskite film. Hence, the target rigid and flexible p-i-n PSCs yielded champion PCEs of 24.99 % and 23.48 %, respectively. More importantly, due to hydrogen bonding between formamidinium and fluorine, the target devices exhibited remarkable thermal, humidity, and operational tracking at maximum power point stabilities. The reduced Young's modulus and residual stress in the perovskite layer also provided excellent bending stability for flexible target devices.

An alternating copolymer of aza[5]helicene, ethylenedioxythiophene, and phenoxazine, featured by matched energy levels, excellent film-forming properties, enhanced Young's modulus and diminished external species diffusion coefficients, was demonstrated for perovskite solar cells, which attain average initial efficiency of 25.5 %, excellent 85 °C thermal stability, and operational stability under the full sunlight.

Abstract

The strategic design of solution-processable semiconducting polymers possessing both matched energy levels and elevated glass transition temperatures is of urgent importance in the progression of thermally robust n-i-p perovskite solar cells with efficiencies exceeding 25 %. In this work, we employed direct arylation polymerization to achieve the high-yield synthesis of three aza[5]helicene-derived copolymers with distinct HOMO energy levels and exceptional glass transition temperatures. Upon integration of these semiconducting polymers into formamidinium lead triiodide-based perovskite solar cells, marked disparities in photovoltaic parameters manifest, primarily stemming from variations in the electrical conductivity and film morphology of the hole transport layers. The p-A5HP-E-POZOD-E copolymer, featuring a main chain comprising alternating repeats of aza[5]helicene, ethylenedioxythiophene, phenoxazine, and ethylenedioxythiophene, attains an initial average efficiency of 25.5 %, markedly surpassing reference materials such as spiro-OMeTAD (23.0 %), PTAA (17.0 %), and P3HT (11.6 %). Notably, p-A5HP-E-POZOD-E exhibits a high cohesive energy density, resulting in enhanced Young's modulus and diminished external species diffusion coefficients, thereby conferring perovskite solar cells with exceptional 85 °C tolerance and operational stability.

Nature Communications, Published online: 10 February 2024; doi:10.1038/s41467-024-45512-8

Nature Communications, Published online: 14 February 2024; doi:10.1038/s41467-024-45649-6