Chen Weijie

For the first time, the accelerated degradation process of flexible perovskite devices is highlighted under the synergistic effect of light and stress. Full-scale theoretical and experimental analysis suggests that carrier localization and dielectric shielding failure are intrinsic triggers of device degradation.

Metal-halide perovskites represent highly efficient and lightweight photovoltaic technology with promising applications in various scenarios. However, their stability is often deteriorated by various external factors in realistic applications, which is particularly severe for flexible devices. Herein this work, the degradation of flexible perovskite devices is focused on under two substantial factors: light and mechanical stress, where the degradation is surprisingly accelerated with simultaneous existence of these factors. Full-scale analysis demonstrates that the mismatch and charge accumulation at the interfaces are direct causes of this device failure. Theoretical simulations reveal that carrier-localization behavior, which is strongly associated with lattice distortion, is the core microscopic factor that destabilizes the device. This finding poses significant challenges to the stability of flexible perovskite devices and other inner strain-sensitive systems, which cannot be simply mitigated by conventional passivation or encapsulation. It is suggested in theoretical studies that this effect may be suppressed by certain physical modulations, such as external electric fields. In general, a better understanding of the degradation mechanisms of realistic flexible and rigid perovskite devices can be contributed in this study and the development of solutions is facilitated to address those challenges.

A series of cross-linked conjugated copolymer donors, named PC2, PC5, and PC8, are designed and synthesized. The cross-linking strategy leads to significant efficiency and mechanical durability improvements for polymer solar cells (PSCs) based on PC2 in comparison with the traditional linear copolymer PR2. These findings indicate that cross-linking method is a promising and straightforward approach for developing high-performance polymer donors for flexible PSCs.

Abstract

A cross-linking strategy can result in a three-dimensional network of interconnected chains for the copolymers, thereby improving their mechanical performance. In this work, a series of cross-linked conjugated copolymers, named PC2, PC5, and PC8, constructed with different ratios of monomers are designed and synthesized. For comparison, a random linear copolymer, PR2 is also synthesized based on the similar monomers. When blended with Y6 acceptor, the cross-linked polymers PC2, PC5, and PC8-based polymer solar cells (PSCs) achieve superior power conversion efficiencies (PCEs) of 17.58%, 17.02%, and 16.12%, respectively, which are higher than that (15.84%) of the random copolymer PR2-based devices. Moreover, the PCE of PC2:Y6-based flexible PSC retains ≈88% of the initial efficiency value after 2000 bending cycles, overwhelming the PR2:Y6-based device with the remaining 12.8% of the initial PCE. These results demonstrate that the cross-linking strategy is a feasible and facile approach to developing high-performance polymer donors for the fabrication of flexible PSCs.

The impact of the alkyl chains of the alkylammonium pesudohalide additives, such as methylammonium thiocyanate (MASCN), ethylammonium thiocyanate (EASCN), and propylammonium thiocyanate (PASCN), on the microstructures, optoelectronic properties of the Dion-Jacobson perovskite films and the performance of the solar cells is investigated. Among the additives, EASCN produces the most efficient and stable solar cells.

Abstract

Dion-Jacobson perovskite (DJP) films suffer from the high structural disorder and non-compact morphology, leading to inefficient and unstable solar cells (SCs). Here, how the alkyl chains of alkylammonium pseudohalide additives including methylammonium thiocyanate (MASCN) and ethylammonium thiocyanate (EASCN), and propylammonium thiocyanate (PASCN), impact the microstructures, optoelectronic properties and the performance of the solar cells is investigated. These additives substantially improve the structural order and the morphology of the DJP films, yielding more efficient and stable solar cells than the control device. They behave quite differently in modifying the morphological features. Particularly, EASCN outstands the additives in terms of the superior morphology, which is compact and uniform and consists of the largest flaky grains. Consequently, the corresponding device delivers a power conversion efficiency (PCE) of 15.27% and maintains ≈86% of the initial PCE after aging in the air for 182 h. Conversely, MASCN as an additive produces uneven DJP film and the device maintains only 46% of the initial PCE. PASCN as an additive produces the finest grains in the DJP film, and the corresponding device yields a PCE of 11.95%. From the economical point of view, it costs 0.0025 yuan per device for the EASCN additive, allowing for cost-effective perovskite solar cells.

The perovskite precursor chemistry is tailored via solvent engineering, which facilitates homogeneous, nucleation, and rapid crystallization of perovskite films in ambient air without necessity of thermal annealing. The room-temperature processed, blade-coated perovskite solar cells deliver a champion efficiency of 19.16% with negligible hysteresis, improved reproducibility, and extended lifespan.

Abstract

The perovskite solar cells (PSCs) are promising for commercialization and practical application. However, high-quality perovskite films are normally fabricated in inert gas-filled glovebox, followed by thermal annealing, which is energy-consuming and thus not cost-effective. In this study, a simple manufacturing strategy is demonstrated to fabricate the highly-crystalline perovskite films in ambient air (a relative humidity of over ≈50%) at room temperature via blade-coating without the subsequent thermal–annealing. The perovskite precursor chemistry is tailored by solvent engineering via employing 2-methoxyethanol, which can strongly coordinate with ammonium halide species, thus forming highly uniform small-sized colloids and facilitating the homogeneous nucleation and rapid crystallization of perovskite films even at room temperature. The resultant PSCs fabricated with ambient-processed, annealing-free MAPbI₃ perovskite films exhibit a champion efficiency up to 19.16% with negligible hysteresis and improved reproducibility, which is on par with the high-temperature annealed counterparts fabricated in N₂, and represented one of the highest reported efficiencies for the room-temperature processed PSCs in ambient air. The unencapsulated devices show extended lifespan over 1000 h with nearly no efficiency loss.

A bowl (corannulene)-assisted ball (fullerene) assembly strategy for solution-processing the favorable C₆₀ electron transport layer (ETL) of perovskite solar cells (PSCs) was deliberately proposed, delivering a highest power conversion efficiency (PCE) of 21.7 % with an excellent light-soaking stability of 1000 hours, which highlights the great potential of corannulene in solubilizing and stabilizing C₆₀ for efficient and stable PSCs.

Abstract

Pristine fullerene C₆₀ is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C₆₀-assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C₆₀, it also plays a critical role in forming C₆₀-corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C₆₀ (SP-C₆₀) ETL. Moreover, the stability of the CC device is far superior to that of the C₆₀-only device because corannulene can retard and curb the spontaneous aggregation of C₆₀. This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C₆₀ ETLs with high promise for fully-SP PSCs.

Publication date: 19 July 2023

Source: Joule, Volume 7, Issue 7

Author(s): Hang Hu, David B. Ritzer, Alexander Diercks, Yang Li, Roja Singh, Paul Fassl, Qihao Jin, Fabian Schackmar, Ulrich W. Paetzold, Bahram Abdollahi Nejand

A deformable coumarin has been successfully employed to passivate anion/cation defects and release residual stress, endowing that phase segregation can be effectively inhibited. Moreover, the benefit of the larger grain size and less trap-assisted recombination, yielding an exceptional efficiency of over 24% for rigid inverted perovskite solar cells and an efficiency of over 23% for flexible inverted perovskite solar cells.

Abstract

The defects and phase segregation in perovskite will significantly reduce the performance and stability of perovskite solar cells (PSCs). In this work, a deformable coumarin is employed as a multifunctional additive for formamidinium–cesium (FA-Cs) perovskite. During the annealing process of perovskite, the partial decomposition of coumarin passivates the Pb²⁺, iodine, and organic cation defects. Additionally, coumarin can affect colloidal size distributions, resulting in relatively large grain size and good crystallinity of target perovskite film. Hence, the carrier extraction/transport can be promoted, trap-assisted recombination is reduced, and energy levels are optimized in target perovskite films. Furthermore, the coumarin treatment can significantly release residual stress. As a result, the champion power conversion efficiencies (PCEs) of 23.18% and 24.14% are obtained for Br-rich (FA_0.88Cs_0.12PbI_2.64Br_0.36) and Br-poor (FA_0.96Cs_0.04PbI_2.8Br_0.12) based devices, respectively. The flexible PSCs based on Br-poor perovskite exhibit an excellent PCE of 23.13%, one of the highest values for flexible PSCs reported to date. Due to the inhibition of phase segregation, the target devices exhibit excellent thermal and light stability. This work provides new insights into the additive engineering of passivating defects, stress relief, and inhibition of phase segregation of perovskite films, offering a reliable method to develop state-of-the-art solar cells.

A surface treatment strategy via heat-induced decomposition of an interlayer to in situ reconstruct perovskite energetics for highly efficient and stable perovskite solar cells is developed, followed by the spontaneous generation of n/n⁻ homojunctions between the perovskite film bulk and the surface region, which significantly promotes hole extraction and suppresses nonradiative recombination of devices.

Abstract

Perovskite solar cells (PSCs) have demonstrated a high power conversion efficiency, however, the large energy loss due to non-radiative recombination is the main challenge for further performance enhancement. Here, a surface treatment strategy is developed by heat-induced decomposition of a thin interlayer 2,7-Naphthaleneditriflate (NAP) to in situ reconstruct perovskite energetics. It is verified that the reconstructed perovskite surface energetics match better with the upper hole transport layer compared to the intrinsic condition. Spontaneous generation of n/n⁻ homojunctions between the perovskite film bulk and the surface region promotes hole extraction, enhancing built-in electric field, and thus significantly suppresses charge recombination at such perovskite hole-selective heterojunctions. Moreover, the surface decomposed fluorine-rich complexes passivate the defects and improve the crystallinity of the perovskite film. These advantages are confirmed by a remarkably improved efficiency from 20.52% for the control device to 23.37% for the treated one with excellent stability. The work provides a promising approach of in situ reconstructing perovskite surface and interface for the design of highly efficient and stable PSCs.

Nature Materials, Published online: 12 June 2023; doi:10.1038/s41563-023-01550-z

Nature Energy, Published online: 12 June 2023; doi:10.1038/s41560-023-01274-z

Publication date: October 2023

Source: Journal of Energy Chemistry, Volume 85

Author(s): Geping Qu, Deng Wang, Xiaoyuan Liu, Ying Qiao, Danish Khan, Yinxin Li, Jie Zeng, Pengfei Xie, Yintai Xu, Peide Zhu, Limin Huang, Yang-Gang Wang, Baomin Xu, Zong-Xiang Xu

This study demonstrates an efficient and reproducible fabrication of all-scalable CH₃NH₃PbI₃ perovskite solar cells in ambient air. Power conversion efficiencies of 19.91% and 17.4% is achieved for rigid and flexible devices, respectively.

Perovskite solar cells (PSCs) are an attractive emerging photovoltaic technology due to their high-performance while being made by low-cost fabrication processes. The most efficient PSCs are small area and made by nonscalable coating method in an inert atmosphere, but these sizes and fabrication conditions are commercially irrelevant. Herein, fabrication of PSCs is reported using only scalable methods, that is, slot-die coating and blade coating methods, all in ambient air. The tolerance to relaxed fabrication conditions is enabled by the use of hydrated nonhalogenated lead source. Resurfacing strategy is then introduced to suppress charge carrier nonradiative recombination and obtained an efficiency of 19.91% for rigid and 17.4% for flexible PSCs by all-scalable fabrication. To the best of our knowledge, these are the highest efficiencies for n–i–p structured MAPbI₃-based PSCs in ambient air using all-scalable method to date. The devices showed excellent tolerance to oxygen and moisture (ISOS-D-1) as well as stable maximum power point operation following burn in a dry air glove box (relative humidity ≈ 20%) without encapsulation.

In inverted perovskite solar cells (PSCs), the hole transport layer (HTL) structure/morphology can greatly affect the quality of the perovskite film. In this paper, a newly crosslinked double-network of PEDOT:PSS@PEGDMA as HTL was used to fabricate Sn–Pb PSCs, and achieve an encouraging power conversion efficiency of 20.9% with good stability.

Abstract

Until now, poly(3,4-ethylenedioxythiophene):poly(styrensulfonate) (PEDOT:PSS) is widely used in Sn–Pb perovskite solar cells (PSCs) due to its many advantages, including high optical transparency, suitable conductivity, superior wettability, and so on. However, the acidic and hydroscopic properties of the PSS component, as well as the incongruous energy level of the hole transport layer (HTL), may lead to unsatisfying interface properties and decreased device performance. Herein, by adding polyethylene glycol dimethacrylate (PEGDMA) into PEDOT:PSS, a newly crosslinked-double-network obtain of PEDOT:PSS@PEGDMA film, which could not only optimize nucleation and crystallinity of Sn–Pb perovskite films, but also suppress defect density and optimize energy level alignment at the HTL/perovskite interface. As a result, the achieves highly efficient and stable mixed Sn–Pb PSCs with an encouraging power conversion efficiency of 20.9%. Additionally, the device can maintain good stability under N₂ atmosphere.

A novel and cost-competitive self-assembled monolayer (SAM) hole transport layer (HTL) is developed for organic solar cells (OSCs). A highest power conversion efficiency of 18.16% was enabled for PM6:BTP-eC9 blends. General applicability was found for typical OSCs systems. Importantly, the SAM can facilitate large-scale HTL fabrication via simple solution immersion, which is attractive for solution-processing large area OSCs.

Abstract

Simplifying solution-processing of bulk-heterojunction (BHJ) organic solar cells (OSCs) via efficient interfacial layers with good generality is in great demand for pushing their large-scale applications. In this study, such a novel and cost-effective self-assembled monolayer (SAM) is reported herein as efficient hole transport layer (HTL) for high efficiency OSCs. The SAM-structured 4-(5,9-dibromo-7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (DCB-BPA) enables not only enhanced photon harvesting in the active layer but also minimized nonradiative recombination losses to improve interface charge extraction/transport. As a consequence, high short-circuit current (≈28.07 mA cm⁻²) is achieved for PM6:BTP-eC9 based OSCs to deliver a champion power conversion efficiency of 18.16%, among the highest values for OSCs using small organic HTLs to date. Importantly, good generality of this SAMs is demonstrated for representative high-efficiency BHJ OSCs systems like PM6:Y6 and PM6:PC₆₁BM, outperforming conventional poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)-based counterparts. Excitingly, the SAM is applicable for large-area HTL processing via immersion method, affording 16.59% efficiency for PM6:BTP-BO-4Cl based OSCs. This study highlights the great potential of engineered SAMs for facile large-scale fabrication of high performance OSCs.

An additive strategy of using potassium formate (HCOOK) as an additive to suppress I₂ impurity defects and passivate perovskite defects is developed. Meanwhile, HCOOK also enlarges the grain size of perovskite, reduces the defects at grain boundaries as well as inhibits the migration of halide ions. The resultant planar n–i–p-structured PSCs exhibit impressive photovoltaic performance.

Abstract

The performance of perovskite solar cells (PSCs) is negatively affected by iodine (I₂) impurities generated from the oxidation of iodide ions in the perovskite precursor powder, solution, and perovskite films. In this study, the use of potassium formate (HCOOK) as a reductant to minimize the presence of detrimental I₂ impurities is presented. It is demonstrated that HCOOK can effectively reduce I₂ back to I⁻ in the precursor solution as well as in the devices under external conditions. Furthermore, the introduced formate anion (HCOO⁻) and alkali metal cation (K⁺) can reduce the defect density within the perovskite film by modulating perovskite growth and passivating electronic defects, significantly prolonging the carrier lifetime and reducing the J–V hysteresis. Consequently, the maximum efficiency of the HCOOK-doped planar n–i–p PSCs reaches 23.8%. After 1000 h of operation at maximum power point tracking under continuous 1 sun illumination, the corresponding encapsulated devices retain 94% of their initial efficiency.

A Lewis-base trans-Ferulic acid (t-FA) is introduced into ≈1.77 eV perovskite precursor solution. Larger perovskite crystals are formed, the residual microstrain is released, and the structure is stabilized with t-FA to inhibit light-induced halide segregation. The optimized device delivers a power conversion efficiency (PCE) of 19.9% and a V _OC of 1.32 V, among the highest performance reported in wide bandgap perovskite devices.

Abstract

Efficient and stable wide bandgap (WBG) perovskite solar cells (PSCs) are imperative for fabricating superior tandem devices. However, small crystal grains and light-induced phase segregation of WBG perovskite result in large open-circuit voltage (V _OC) deficits, critically impeding the development of the related devices. Herein, the effective functional groups of Lewis-base trans-Ferulic acid (t-FA) are employed to release the residual microstrain in the perovskite lattice. Larger perovskite crystals are formed by strengthening the interaction between the perovskite solute and solution. The lattice structure is stabilized to suppress light-induced halide segregation. Finally, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈1.77 eV is increased from 17.33% to 19.31% with the enhancement of V _OC. Moreover, replacing a mixture of MeO-2PACZ and Me-4PACZ as the hole transporting layer (HTL), the PCE further lifts to 19.9% and V _OC is 1.32 V, one of the highest performances reported for WBG PSCs, especially for devices prepared entirely by solution spin-coating. Therefore, this study provides a practicable alternative for realizing efficient WBG PSCs, which can contribute to the growth of perovskite-based tandem devices.

The amino naphthalene sulfonates (ANS) molecules are incorporated as a dipolar interlayer at the buried interface to fabricate CsPbI₃ perovskite indoor photovoltaics (PIPVs). The strong ion–dipole interaction between polar ANS molecules and ionic perovskites enables the target PIPVs to deliver a record indoor PCE of up to 41.2% (P _out:137.66 µW cm⁻²) under a standard LED light source (2956 K, 1062 lux).

Abstract

Metal halide perovskites are ideal candidates for indoor photovoltaics (IPVs) because of their easy-to-adjust bandgaps, which can be designed to cover the spectrum of any artificial light source. However, the serious non-radiative carrier recombination under low light illumination restrains the application of perovskite-based IPVs (PIPVs). Herein, polar molecules of amino naphthalene sulfonates are employed to functionalize the TiO₂ substrate, anchoring the CsPbI₃ perovskite crystal grains with a strong ion–dipole interaction between the molecule-level polar interlayer and the ionic perovskite film. The resulting high-quality CsPbI₃ films with the merit of defect-immunity and large shunt resistance under low light conditions enable the corresponding PIPVs with an indoor power conversion efficiency of up to 41.2% (P _in: 334.11 µW cm⁻², P _out: 137.66 µW cm⁻²) under illumination from a commonly used indoor light-emitting diode light source (2956 K, 1062 lux). Furthermore, the device also achieves efficiencies of 29.45% (P _out: 9.80 µW cm⁻²) and 32.54% (P _out: 54.34 µW cm⁻²) at 106 (P _in: 33.84 µW cm⁻²) and 522 lux (P _in: 168.21 µW cm⁻²), respectively.

An organic small-molecule octafluoro-1,6-hexanediol diacrylate (OF-HDDA) is introduced to in situ crosslink forming a polymer (POF-HDDA), which anchors uncoordinated lead ions and prevents lead leakage from water and oxygen invasion, and concurrently improves the long-term stability of the corresponding devices.

Abstract

High-performance perovskite solar cells have demonstrated commercial viability, but still face the risk of contamination from lead leakage and long-term stability problems caused by defects. Here, an organic small molecule (octafluoro-1,6-hexanediol diacrylate) is introduced into the perovskite film to form a polymer through in situ thermal crosslinking, of which the carbonyl group anchors the uncoordinated Pb²⁺ of perovskite and reduces the leakage of lead, along with the −CF₂− hydrophobic group protecting the Pb²⁺ from water invasion. Additionally, the polymer passivates varieties of Pb-related and I-related defects through coordination and hydrogen bonding interactions, regulating the crystallization of perovskite film with reduced trap density, releasing lattice strain, and promoting carrier transport and extraction. The optimal efficiencies of polymer-incorporated devices are 24.76 % (0.09 cm²) and 20.66 % (14 cm²). More importantly, the storage stability, thermal stability, and operational stability have been significantly improved.

Nature, Published online: 08 June 2023; doi:10.1038/s41586-023-06278-z