Perovskite Precursor Research Articles

High‐Efficiency Perovskite Solar Cells Enabled by Guanylation Reaction for Removing MACl Residual and In‐Situ Forming 2D Perovskite

The thermodynamical deprotonation of methylammonium chloride (MACl) has several detrimental influences on the quality of formamidinium (FA+)‐based perovskite, which limits both efficiency and stability of inverted perovskite solar cells (IPSCs). Herein, a new additive strategy was developed by introducing methyl carbamimidothioate hydroiodide (MCH) into perovskite precursor, where guanylation reaction occurred between MCH and MACl to form a new intermediate of methyl‐substituted guanidine (MSG). MSG could then bond with undercoordinated Pb2+ to in‐situ form a two‐dimensional (2D) perovskite, which would promote the growth and crystallization of three‐dimensional (3D) perovskite with higher crystallinity, lower defect‐states density and superior stability. Finally, the MCH‐treated IPSC with a small area (0.09 cm2) achieved an impressive power conversation efficiency (PCE) of 26.81% (certified as 26.02%), which is one of the highest PCEs reported to date. The large area MCH‐treated device (1.00 cm2) also obtained a high PCE of 24.36%. Moreover, the unencapsulated and MCH‐treated device exhibited excellent operational stability, maintaining 91.95% and 97.06% of their initial efficiencies after aging in air and a nitrogen‐filled atmosphere at 85 oC for 1200 h. The encapsulated MCH‐treated devices retained 94.25% of its initial efficiency after continuously tracking at the maximum power‐point for 1200 h in air.

High-Efficiency Perovskite Solar Cells Enabled by Guanylation Reaction for Removing MACl Residual and In-Situ Forming 2D Perovskite.

The thermodynamical deprotonation of methylammonium chloride (MACl) has several detrimental influences on the quality of formamidinium (FA+)-based perovskite, which limits both efficiency and stability of inverted perovskite solar cells (IPSCs). Herein, a new additive strategy was developed by introducing methyl carbamimidothioate hydroiodide (MCH) into perovskite precursor, where guanylation reaction occurred between MCH and MACl to form a new intermediate of methyl-substituted guanidine (MSG). MSG could then bond with undercoordinated Pb2+ to in-situ form a two-dimensional (2D) perovskite, which would promote the growth and crystallization of three-dimensional (3D) perovskite with higher crystallinity, lower defect-states density and superior stability. Finally, the MCH-treated IPSC with a small area (0.09 cm2) achieved an impressive power conversation efficiency (PCE) of 26.81% (certified as 26.02%), which is one of the highest PCEs reported to date. The large area MCH-treated device (1.00 cm2) also obtained a high PCE of 24.36%. Moreover, the unencapsulated and MCH-treated device exhibited excellent operational stability, maintaining 91.95% and 97.06% of their initial efficiencies after aging in air and a nitrogen-filled atmosphere at 85 oC for 1200 h. The encapsulated MCH-treated devices retained 94.25% of its initial efficiency after continuously tracking at the maximum power-point for 1200 h in air.

Enhancing Flexibility, Long-Term Stability, and Efficiency in Full Air Fabricated Perovskite Solar Cells via Multifunctional Fluorinated Polyurethane Additives.

Perovskite films often suffer from surface and grain boundary defects, including uncoordinated ions, lattice distortions, and dangling bonds, coupled with lattice distortions due to solvent volatilization anisotropy and the thermal expansion coefficient. Such defects severely compromise both the photovoltaic efficiency and long-term solar cell stability. Here, fluorinated polyurethane (FPU) was synthesized and introduced into the perovskite precursor as a multifunctional additive. Excess Pb2+ ions interact with the carbonyl group (C═O) of FPU, thereby reducing nonradiative recombination. The perovskite and FPU form various hydrogen bonds via MA+ with F and -NH with -I. This multiplies the passivation of grain boundary defects, increases grain size, reduces defect density, releases residual lattice stress, and facilitates charge transport. Accordingly, the power conversion efficiency of the FPU-modified perovskite solar cells (PSCs) on rigid substrates and flexible substrates reached 21.18 and 17.76%, respectively. Notably, the long-chain C-F compound, which constructs a moisture-resistant barrier, could inhibit moisture corrosion in the perovskite films. After 2000 h of storage at ambient temperature in dark, the PSCs's initial efficiency still remained 82%. Additionally, after it undergoes 300 bending cycles (r = 0.7 cm), the device maintains 92.4% of its initial efficiency.

Regulating Compressive Strain Enables High‐Performance Tin‐Based Perovskite Solar Cells

AbstractTin (Sn)‐based perovskites have emerged as promising alternatives to lead (Pb)‐based perovskites in thin‐film photovoltaics due to their comparable properties and reduced toxicity. Strains in perovskites can be tailored to modulate their optoelectronic properties, but mechanisms for the effects of strains on Sn‐based perovskite films and devices are unrevealed and corresponding strain engineering is unexplored. Herein, a strain engineering strategy is developed through incorporating 4‐fluorobenzylammonium halide salts (FBZAX, X = I, Br, Cl) into the perovskite precursor to regulate the strain effects in resultant Sn‐based perovskite films. It is found that a moderate level of compressive strain achieved by FBZABr alleviates the dislocations within perovskites to enhance carrier transport and reduces the defect density to prolong carrier lifetime. These improvements enable a champion efficiency exceeding 14% of Sn‐based perovskite solar cells with excellent operational stability.

Sn-Pb Perovskite with Strong Light and Oxygen Stability for All-Perovskite Tandem Solar Cells.

Research on mixed Sn-Pb perovskite solar cells (PSCs) is gaining significant attention due to their potential for high efficiency in all-perovskite tandem solar cells. However, Sn2+ in Sn-Pb perovskite is susceptible to oxidation, leading to a high defect density. The oxidation primarily occurs through two pathways: one involving a reaction with oxygen, and the other related to iodine defects, which generate I2 and further accelerate the oxidation of Sn2⁺, greatly reducing stability. First, to tackle the photo-stability issues caused by iodine defects, amber acid (AA) is screened as the additive. The Carboxyl group on AA can strongly coordinate with Sn2+, reinforcing the Sn─I bond and electrostatically interacting with negatively charged defects. This interaction inhibits the photoinduced formation of I2 and the subsequent oxidation of Sn2+, thereby enhancing the stability of Sn─Pb PSCs under continuous illumination. Building on the foundation of AA, a reductive sulfhydryl group is introduced to synthesize thiomalic acid (TA). It inhibits the formation of Sn4+ in both the perovskite precursor and the perovskite film, thereby improving air stability while maintaining strong photostability. Consequently, single PSCs achieved a champion efficiency of 22.7%. The best-performing two-terminal all-perovskite tandem solar cell achieved a power conversion efficiency of 28.6% with improved operational stability.

Unraveling the colloidal composition of perovskite precursor solutions and its impact on film formation

Unraveling the colloidal composition of perovskite precursor solutions and its impact on film formation

Efficient and Stable Inverted Perovskite Solar Cells Enabled by Inhibiting Voids via a Green Additive.

The buried interface in inverted perovskite solar cells (PSCs) is critical for determining device performance. However, during annealing, the perovskite crystallized downward from the film's top surfaces, and the use of dimethyl sulfoxide (DMSO) often resulted in voids at the perovskite bottom surface, which negatively impacted PSC performance. In this study, a green solid-state additive, piracetam (PA), was introduced into a perovskite precursor to reduce void formation. Due to the stronger interaction with perovskite components than DMSO, nonvolatile PA could remain within the perovskite films during thermal annealing to avoid volume collapse, thereby preventing the formation of voids at the buried interface as well as passivating the defects of undercoordinated Pb2+. Additionally, the introduction of PA could effectively enhance the crystallization of perovskite, leading to an improved quality of the perovskite films and depressed nonradiative recombination. As a result, the power conversion efficiency (PCE) of PSCs increased significantly from 20.95 to 23.42% with excellent operational and thermal stability.

Application of PACz-Based Self-Assembled Monolayer Materials in Efficient Perovskite Solar Cells.

Due to the advantages of low interface resistance, high work function, and high stability, PACz family materials have developed rapidly in p-i-n structure perovskite solar cells (PSCs) in recent years. Numerous studies have shown that PSCs prepared on the basis of PACz family materials or their derivatives as hole transport layers (HTLs) generally exhibit superior performance compared to PSCs prepared on the basis of organic HTL PTAA and inorganic HTL NiOx, especially in terms of stability, demonstrating unparalleled charm. Since the application of PACz-like molecule V1036 as a HTL in PSCs in 2018, research reports on high-performance PSCs based on the PACz family HTL have been widely disseminated. Currently, PSCs based on the PACz HTL exhibit a world record value of 26.7% power conversion efficiency (PCE), breaking the long-standing world record held by n-i-p-structured PSCs, indicating its great potential for application in PSCs. The main problem with using PACz as a HTL is that it exhibits poor wettability toward perovskite precursor solutions, is sensitive to the thickness of the HTL and the roughness of the substrate, has poor thermal stability, and lacks preparation methods, making it difficult to achieve large-area device fabrication. This review summarizes the outstanding achievements of PACz to date, describes the mechanism and unique properties of PACz in PSCs, and looks forward to the future development prospects of PACz.

Extending Shelf-Life of Two-Step Method Precursor Solutions through Targeted Regulation for Highly Efficient and Reproducible Perovskite Solar Cells.

Precursor solution aging process can cause significant influence on the photovoltaic performance of perovskite solar cells (PVSCs). Notably, we first observe that the aging phenomenon is more severe in the precursor of two-step sequential method compared to that in one-step method due to that the protic solvent isopropanol facilitates amine-cation side reaction and iodide ions oxidation. Herein, we report a novel approach for selectively stabilizing both organic amine salt and lead iodide (PbI2) precursor solutions in two-step method. The introduction of benzene-1,3-dithiol into organic amine salt solution can mitigate amine-cation side reactions due to the formation of an acidic and reducing environment. Simultaneously, decamethylferrocene (FcMe10/FcMe+ 10) pair can act as a redox shuttle in PbI2 solution to concurrently oxidize Pb0 and reduce I2 in cyclic manner. Consequently, the PVSCs device fabricated from ameliorative precursor solutions demonstrates superior power conversion efficiency of 25.31 %, retaining 95 % of its efficiency after 21 days of solution aging. Moreover, the unencapsulated devices maintain 85 % of primitive efficiency for 1500 h at maximum power point tracking under continuous illumination. This work establishes a fundamental guidance and scientific direction for the stabilization of two-step perovskite precursor solutions.

Extending Shelf‐Life of Two‐Step Method Precursor Solutions through Targeted Regulation for Highly Efficient and Reproducible Perovskite Solar Cells

AbstractPrecursor solution aging process can cause significant influence on the photovoltaic performance of perovskite solar cells (PVSCs). Notably, we first observe that the aging phenomenon is more severe in the precursor of two‐step sequential method compared to that in one‐step method due to that the protic solvent isopropanol facilitates amine‐cation side reaction and iodide ions oxidation. Herein, we report a novel approach for selectively stabilizing both organic amine salt and lead iodide (PbI2) precursor solutions in two‐step method. The introduction of benzene‐1,3‐dithiol into organic amine salt solution can mitigate amine‐cation side reactions due to the formation of an acidic and reducing environment. Simultaneously, decamethylferrocene (FcMe10/FcMe+10) pair can act as a redox shuttle in PbI2 solution to concurrently oxidize Pb0 and reduce I2 in cyclic manner. Consequently, the PVSCs device fabricated from ameliorative precursor solutions demonstrates superior power conversion efficiency of 25.31 %, retaining 95 % of its efficiency after 21 days of solution aging. Moreover, the unencapsulated devices maintain 85 % of primitive efficiency for 1500 h at maximum power point tracking under continuous illumination. This work establishes a fundamental guidance and scientific direction for the stabilization of two‐step perovskite precursor solutions.

Cation reactivity inhibits perovskite degradation in efficient and stable solar modules.

Perovskite solar modules (PSMs) show outstanding power conversion efficiencies (PCEs), but long-term operational stability remains problematic. We show that incorporating N,N-dimethylmethyleneiminium chloride into the perovskite precursor solution formed dimethylammonium cation and that previously unobserved methyl tetrahydrotriazinium ([MTTZ]+) cation effectively improved perovskite film. The in situ formation of [MTTZ]+ cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes. The optimized PSMs achieved a record (certified) PCE of 23.2% with an aperture area of 27.2 cm2, with a stabilized PCE of 23.0%. The encapsulated PSM retained 87.0% of its initial PCE after ~1900 hours of maximum power point tracking at 85°C and 85% relative humidity under 1.0-sun illumination.

Functional design and understanding of effective additives for achieving high-quality perovskite films and passivating surface defects

Achieving high-quality perovskite films without surface defects is regarded as a crucial target for the development of durable high-performance perovskite solar cells. Additive engineering is commonly employed to simultaneously control the growth of perovskite crystals and passivate defects. Here, 4-(trifluoromethyl)benzoic anhydride (4-TBA) composed of benzene rings functionalized with carbonyl and trifluoromethyl groups was used as an example additive to study the characteristics of additives used for producing high-quality perovskites and controlling their surface properties. The interaction between 4-TBA and perovskite precursor materials was investigated using density functional theory (DFT) simulations. The electron-rich carbonyl group efficiently passivated the under-coordinated lead-ion defects. Additionally, hydrogen bonding between trifluoromethyl and organic cations prevents the generation of cation vacancies. Because of its intrinsic hydrophobicity, the trifluoromethyl group simultaneously improves the moisture and heat stability of the film. 4-TBA serves as a universal modifier for various perovskite compositions. The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) based on methylammonium (MA) with 4-TBA was improved from 16.15% to 19.28%. Similarly, the PCE of inverted PSCs based on a cesium formamidinium MA (CsFAMA) perovskite film increased from 20.72% to 23.58%, upon addition of 4-TBA. Furthermore, the moisture and thermal stability of 4-TBA-treated films and devices was significantly enhanced, along with prolonged device performance. Our work provides guidance on selecting the structure and functional groups that are essential for surface defect passivation and the production of high-quality perovskites.

Low-temperature crosslinked hole transport material for high-performance inverted perovskite solar cells

Hole transport materials (HTMs) play a crucial role in the development of high-performance inverted perovskite solar cells (PSCs) by facilitating hole transport, passivating defects, and tuning crystallization. Achieving high efficiency and stability remains a key challenge for the PSCs. Crosslinked HTMs combine the efficiency of small molecules with enhanced environmental stability, however, a significant challenge in developing crosslinked HTMs for PSCs is the high temperature required for crosslinking. In this work, we synthesized a concise crosslinkable HTM, Tetrastyrenebiphenyldiamine (TPDA), based on a biphenyl core with four styrene groups, using a one-step method. TPDA can be crosslinked through an annealing process at 100℃ for 10 min without the need for any dopants or initiators. Interestingly, the compact films formed in the anneal process and the excellent spreadability for the perovskite precursor solution leading to the high-quality perovskite films, as a result, the inverted devices based on CL-TPDA achieve a champion power conversion efficiency (PCE) of 21.4%. Furthermore, the stability of the devices without encapsulation has notably improved. The PCE maintains over 85% of its initial value after 1000 h of storage in ambient air (25℃, relative humidity about 50%).

Crystallization Control to Prepare Uniform CsPbI2Br Thin Films for High-Efficiency Perovskite Solar Cells.

All-inorganic perovskite solar cells (PSCs) face challenges related to film inhomogeneity, which arises from nonideal crystallization. This issue significantly impedes the advancement of all-inorganic PSCs. In this study, we observed that during the crystallization process of CsPbI2Br, the Br-rich intermediate phase is often preferentially deposited, leading to an uneven distribution in the out-of-plane direction of the perovskite film. To address this issue, crown ether molecules (dibenzo-18-crown-6) were introduced into the perovskite precursor solution. The complexation of crown ether with Cs cations and Br anions optimizes the crystallization sequence of the perovskite, ensuring that the intermediate phase closely conforms to the standard stoichiometric ratio. This adjustment significantly mitigates the problem of uneven halogen ion distribution along the out-of-plane direction. Furthermore, the crown ether thermally decomposes during the high-temperature annealing process, thereby not affecting the composition of the final perovskite film. Following crown ether treatment, the efficiency of the PSCs reached 14.08%, and the unpackaged devices maintained 80% of their initial efficiency after 1000 h of exposure to light in an atmospheric environment.

Synergistic Passivation of Bulk and Interfacial Defects Improves Efficiency and Stability of Inverted Perovskite Solar Cells

Defects both in bulk and at the interfaces serve as charge trapping sites for nonradiative recombination and as ion migration pathways, resulting in degradation of perovskite solar cell efficiency and stability. In this work, a strategy for simultaneous passivation of both bulk and interfacial defects is reported. For bulk passivation polystyrene (PS) is used as an additive in the perovskite precursor which reduces the structural defects by forming larger defect‐free grains. While the F‐PEAI cation is used to passivate the interfacial defects, present at both perovskite HTL/ETL interfaces. Furthermore, by conducting control measurements with just bulk modification (PS), just interface modification (F‐PEAI), and a combination of both, the role of individual defect passivation strategies is decoupled. As a result of simultaneous bulk as well as interfacial passivation, the modified perovskite solar cell shows the highest efficiency of 22.32% with a high Voc of 1.14 V and fill factor of 80%. Moreover, the cells have excellent stability retaining 92% and 99% of their initial efficiency after 1008 h and 560 h under ISOS‐ D1 and D2 storage conditions. These results highlight the importance of simultaneous bulk and interfacial passivation for improving solar cell efficiency and stability.

Low-cost green antisolvent with an ultrawide processing window for efficient and stable perovskite solar cells

Antisolvent engineering is one of the most useful strategies to get high-efficiency perovskite solar cells (PSCs). Nevertheless, the most present commonly used effective antisolvents, such as chlorobenzene and diethyl ether, are toxic and expensive. Moreover, these antisolvents applied in PSCs are rather restricted due to their narrow processing window. Herein, we report a low-cost green antisolvent isopropanol (IPA) that displays ultrawide processing window, which dramatically enhances the reproducibility of PSCs. The highest power conversation efficiency of PSCs treated by IPA can reach as high as 24.8%. The origin of IPA effects is further disclosed by the intermolecular hydrogen-bonding force between IPA and DMF/DMSO, and the force can effectively remove DMF/DMSO in the spinning perovskite precursor film and helpfully enhance perovskite crystal growth with less carrier recombination as demonstrated by using various techniques. Our results here demonstrate a cheap green antisolvent for reproducible, high-efficient, stable PSCs and also provide an in-depth understanding the significant role of antisolvent in the fabrication of PSCs.

Fluorocarbon‐based Solvent‐Bath Annealing for High‐Performance Perovskite Photovoltaics

AbstractThermal annealing is a critical process in producing high‐quality perovskite films for high‐performance perovskite solar cells. Conventional TA presents challenges such as delayed heat transfer, leading to unwanted crystal growth and hindering processing scalability. Solvent‐bath annealing is an attractive approach that can improve heat transfer and promote perovskite crystallization by immersing the as‐deposited precursor film in a liquid medium. In this study, fluorocarbon‐based solvents are developed as novel solvent baths for uniform heat flow through omnidirectional annealing. In addition, the previously neglected solvent‐to‐solvent interaction between fluorocarbon and solvents for perovskite precursor is investigated by comparing two fluorocarbon solvents. By increasing the solvent‐solvent interaction, higher quality perovskite films with increased crystallinity, improved perovskite transition, and reduced film defects are achieved. As a result, the perovskite solar cells exhibited an increased power conversion efficiency with excellent reproducibility. These findings suggest that the selection of suitable solvent bath is promising for further improving perovskite quality and device performance.

Studying the effect of ambient temperature variations on perovskite precursor film formation using different antisolvents

This study investigates the sensitivity of two antisolvents to ambient temperature fluctuations during the fabrication of triple-cation perovskite thin films. Chlorobenzene (CB) and ethyl acetate (EA) were employed as antisolvents in the preparation of perovskite solar cells (PSCs) under identical ambient temperature variation conditions. The experimental results reveal that the quality of the perovskite films does not exhibit a consistent trend in response to ambient temperature changes depending on the antisolvent used. When CB was used as the antisolvent, the highest-performing device, produced at an ambient temperature of 18 °C, achieved a power conversion efficiency (PCE) of 19.9 %. In contrast, when EA was employed as the antisolvent, the highest-performing device was fabricated at 25 °C, reaching a PCE of 20.5 %. Furthermore, when the ambient temperature exceeded 30 °C, all films prepared with either antisolvent exhibited significant cracking, indicating that elevated temperatures adversely affect perovskite film formation. To further investigate the mechanism through which ambient temperature affects the film-forming process, antisolvents at varying temperatures were used during perovskite film preparation to simulate transient temperature increases during formation. This study reveals that the impact of ambient temperature variations on perovskite film formation does not exhibit a uniform trend but is significantly influenced by the choice of antisolvent. Moreover, this work offers valuable insights for optimizing the fabrication of high-quality perovskite thin films.

Boosting Efficiency to 22.73%: Unraveling the Role of Solvent Environment in Low‐Dimensional Perovskites Through Competitive Bonding Interactions

AbstractIt is reported that the solvent environment exerts a significant influence on the property of perovskite precursor solution and resultant film, which is more pronounced in more complex low‐dimensional perovskites. Four solvent additives with varying basicity are introduced to instigate a tug‐of‐war among bonding interactions, thereby exploring the systematic effect of the solvent environment on the growth of quantum wells and the photoelectric properties of the resultant low‐dimensional perovskite films. A governing principle that diverges significantly from those previously documented for three‐dimensional perovskites is elucidated in low‐dimensional perovskites. When coordination interactions predominate in the solvent environment, the emergence of a two‐dimensional GA2PbI4 transitional phase is fostered to facilitate subsequent transformation into the desirable ACI phase, and the perovskite crystallization kinetics is retarded to improve the film quality. Hence, the highest power conversion efficiency (PCE) of 22.73% is obtained for GA(MA)nPbnI3n+1 (n = 5) based solar cells with a p‐i‐n structure. The PCE achieved in this work is a record among the reported low‐dimensional perovskite solar cells.

Targeted synergistic chemical bonding strategy for Efficient and stable CsPbI3-based perovskite solar cells

Regulating the crystallization process of perovskite film and suppressing iodine-related defects hold significant importance in improving the efficiency and stability of CsPbI3-based perovskite solar cells (PSCs), thereby endowing their more potential for commercial applications. Herein, we introduced 2-Aminoethyl methylsulfone hydrochloride (AMS) into the perovskite precursor solution to establish targeted synergistic chemical bonding involving Lewis acid-base interactions and hydrogen bonds with CsPbI3 perovskite. We emphasize the importance of the DMAPbI3 intermediate phase for the crystal quality of CsPbI3 perovskite, and reveal that diminishing the size of Pb-I framework colloids in precursor solution can facilitate the formation of DMAPbI3 and optimize the crystallization process of CsPbI3 perovskite. Simultaneously, we demonstrate the generation of high valence iodine defects due to the photoinduction, and prove that constructing N-H···I hydrogen bond can effectively passivate the iodine-related defects. Consequently, the CsPbI3-based PSCs display an impressive power conversion efficiency of 19.59% along with markedly improved stability. Our finding presents a feasible strategy for managing perovskite crystallization and mitigating the defects-induced perovskite degradation, thus promoting the commercialization of CsPbI3-based PSCs.