Chen Weijie

Lower dimensional structure and lower formation energy of the phenyl-based perovskites are demonstrated by simply replacing the methylamine (MA) group with the formamidine (FA) group. Therefore, a more complete conversion of the PbI₂ residue using a formamidine (FA) functional group-based benzamidine hydrochloride (PFACl) post-treatment is realized, enabling the two-step-processed FAPbI₃ perovskite films with low surface roughness, narrow surface potential distribution, low trap density, fast charge transfer as well as good stability. As a result, more effective defect passivation is realized and thus contributes to scalable, efficient, and stable perovskite photovoltaics.

Abstract

Converting PbI₂ residues into low-dimensional perovskites through post-treatment with ammonium-based large cations can passivate 3D perovskites, thus has emerged as an effective strategy to improve the performance of perovskite solar cells (PSCs). Herein, a dramatically improved efficiency is demonstrated for PSCs based on a two-step-processed FAPbI₃ perovskite via post-treatment with formamidinium (FA)-based benzamidine hydrochloride (PFACl), outperforming the commonly used methylamine (MA)-based benzylamine hydrochloride (PMACl). With an in-depth exploration of the crystal structures and morphology changes of the FAPbI₃ perovskite upon the PFACl post-treatment, the preferential formation of 1D rather than 2D structures on the 3D perovskite film is identified. In contrast to the 2D counterpart, the more energetically favorable 1D structure enables a more effective elimination of PbI₂ residues. As a consequence, the PFACl-induced 1D/3D perovskite film is endowed with smoother morphology, more uniform surface potential distribution, lower trap density, faster charge transfer, and better film stability than the PMACl-induced 2D/3D perovskite and control films, demonstrating champion efficiencies of 24.9% for a small-size PSC, 23.6% for a 1 cm² large-size PSC, and 21.2% for a 5 × 5 cm² mini-module, which is the highest among the perovskite solar mini-modules using the two-step deposition method.

Material purity impacts optoelectronic properties; trace water in chemicals affects perovskite formation, influencing performance. This study unveils the significance of water content in PbI₂, affecting crystallization and texture and ultimately decreasing hole mobility. Imbalanced hole–electron mobility limits device performance. Certified PCEs of 24.3% and 22.9% for small and larger aperture solar cells are achieved by fine-controlling water content in PbI₂.

Abstract

The experimental replicability of highly efficient perovskite solar cells (PSCs) is a persistent challenge faced by laboratories worldwide. Although trace impurities in raw materials can impact the experimental reproducibility of high-performance PSCs, the in situ study of how trace impurities affect perovskite film growth is never investigated. Here, light is shed on the impact of inevitable water contamination in lead iodide (PbI₂) on the replicability of device performance, mainly depending on the synthesis methods of PbI₂. Through synchrotron-based structure characterization, it is uncovered that even slight additions of water to PbI₂ accelerate the crystallization process in the perovskite layer during annealing. However, this accelerated crystallization also results in an imbalance of charge-carrier mobilities, leading to a degradation in device performance and reduced longevity of the solar cells. It is also found that anhydrous PbI₂ promotes a homogenous nucleation process and improves perovskite film growth. Finally, the PSCs achieve a remarkable certified power conversion efficiency of 24.3%. This breakthrough demonstrates the significance of understanding and precisely managing the water content in PbI₂ to ensure the experimental replicability of high-efficiency PSCs.

Succinic acid derivative with multiple active sites and optimal spatial positions maximizes the defect binding energy, improves the film quality, and depresses the non-radiative recombination of the perovskite, giving a record efficiency of 25.41% for RbCsFAMA-based quadruple-cation perovskite devices.

Abstract

Minimizing interfacial charged traps in perovskite films is crucial for reducing the non-radiative recombination and improving device performance. In this study, succinic acid (SA) derivatives varying active sites and spatial configurations are designed to modulate defects and crystallization in perovskite film. The SA derivative with two symmetric Br atoms, dibromosuccinic acid (DBSA), exhibits the optimal spatial arrangement for defect passivation. Experimental and theoretical results indicate that the carboxyl group and atomic Br in DBSA synergistically interact with the under-coordinated Pb²⁺. Moreover, the strong electronegativity of Br efficiently stabilizes the formamidinium cation via electrostatic interaction. Consequently, film quality is significantly improved and non-radiative recombination is markedly depressed, resulting in a photoluminesence lifetime of exceeding 4 µs of and a carrier diffusion length of 3 µm. An exceptional efficiency of 25.41% (certified at 25.00%) along with a high fill factor of 84.39% and excellent long-term operational stability have been achieved finally.

A released distortion of 2D perovskite ((NAM)₂PbI₄) with large Pb-I-Pb angle is realized via weakening the hydrogen bonding between organic spacer and [PbI₆]⁴⁻ octahedron. It leads to the formation of well-matched heterointerface between (002) facet of (NAM)₂PbI₄ and (100) plane of FAPbI₃, which lowers the crystal formation energy and triggers the epitaxial growth α-FAPbI₃. An impressive power conversion efficiency of 25.4% (certified 25.2%) is achieved by the target perovskite solar cells, along with enhanced stability.

Abstract

Although the FAPbI₃ perovskite system exhibits an impressive optoelectronic characteristic and thermal stability because of its energetically unstable black phase at room temperature, it is considerably challenging to attain a controllable and oriented nucleation of α-FAPbI₃. To overcome this challenge, a 2D perovskite with a released inorganic octahedral distortion designed by weakening the hydrogen interactions between the organic interlayer and [PbI₆]⁴⁻ octahedron is presented in this study. A highly matched heterointerface can be formed between the (002) facet of the 2D structure and the (100) crystal plane of the cubic α-FAPbI₃, thereby lowering the crystallization energy and inducing a heterogeneous nucleation of α-FAPbI₃. This “epitaxial growth” mechanism results form the highly preferred crystallographic orientation of the (100) facets, improved crystal quality and film uniformity, substantially increased charge transporting characteristics, and suppressed nonradiative recombination losses. An impressive power conversion efficiency (PCE) of 25.4% (certified 25.2%) is achieved using target PSCs, which demonstrates outstanding ambient and operational stability. The feasibility of this strategy is proved for the scalable deposition of homogeneous and high-quality perovskite thin films by demonstrating the remarkably increased PCE of the large-area perovskite solar module, from 18.2% to 20.1%.

Publication date: 20 December 2023

Source: Joule, Volume 7, Issue 12

Author(s): Yang Jiang, Tian-Fei Xu, Hong-Qiang Du, Mathias Uller Rothmann, Zhi-Wen Yin, Ye Yuan, Wan-Chun Xiang, Zhi-Yi Hu, Gui-Jie Liang, Sheng-Zhong Liu, Mohammad Khaja Nazeeruddin, Yi-Bing Cheng, Wei Li

Alkoxythiophene additives are developed to induce the fibrillization of a series of BDT-type polymer donors for organic solar cells, demonstrating generally increased efficiency, with the PM6/L8-BO binary device reaching 19.2%.

Abstract

Realizing fibrillar molecular framework is highly encouraged in organic solar cells (OSCs) due to the merit of efficient charge carrier transport. This is however mainly achieved via the chemical structural design of photovoltaic semiconductors. In this work, through the utilization of three alkoxythiophene additives, T-2OMe, T-OEH, and T-2OEH, the intermolecular interactions among a series of BDT-type polymer donors, i.e., PM6, D18, PBDB-T, and PTB7-Th, are tuned to self-assemble into nanofibrils during solution casting. X-ray technique and molecular dynamics simulation reveal that the alkoxythiophene with (2-ethylhexyl)oxy (─OEH) chains can attach on the 2-ethylhexyl (EH) chains of these polymer donors and promote their self-assembly into 1D nanofibrils, in their neat films as well as photovoltaic blends with L8-BO. By adapting these fibrillar polymer donors to construct pseudo-bulk heterojunction (P-BHJ) OSCs via layer-by-layer deposition, generally improved device performance is seen, with power conversion efficiencies enhanced from 18.2% to 19.2% (certified 18.96%) and from 17.9% to 18.7% for the PM6/L8-BO and D18/L8-BO devices, respectively. This work provides a physical approach to promote the fibrillar charge transport channels for efficient photovoltaics.

A fully aromatic carbazole-based self-assembled monolayer, denoted as MeO-PhPACz, is employed as a hole-selective layer (HSL) in inverted wide-band gap perovskite solar cells (PSCs). The fully aromatic configuration is crucial in promoting the formation of a dense and highly ordered HSL, improving hole extraction/transport efficiency. The optimized wide-band gap PSCs attain a power conversion efficiency (PCE) of 21.10 % and excellent UV resistance.

Abstract

Ultraviolet-induced degradation has emerged as a critical stability concern impeding the widespread adoption of perovskite solar cells (PSCs), particularly in the context of phase-unstable wide-band gap perovskite films. This study introduces a novel approach by employing a fully aromatic carbazole-based self-assembled monolayer, denoted as (4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)phosphonic acid (MeO-PhPACz), as a hole-selective layer (HSL) in inverted wide-band gap PSCs. Incorporating a conjugated linker plays a pivotal role in promoting the formation of a dense and highly ordered HSL on substrates, facilitating subsequent perovskite interfacial interactions, and fostering the growth of uniform perovskite films. The high-quality film could effectively suppress interfacial non-radiative recombination, improving hole extraction/transport efficiency. Through these advancements, the optimized wide-band gap PSCs, featuring a band gap of 1.68 eV, attain an impressive power conversion efficiency (PCE) of 21.10 %. Remarkably, MeO-PhPACz demonstrates inherent UV resistance and heightened UV absorption capabilities, substantially improving UV resistance for the targeted PSCs. This characteristic holds significance for the feasibility of large-scale outdoor applications.

A dual-strategy of self-assembly 3D/0D quasi-core–shell structure and in situ excess PbI₂ has been introduced in FAPbI₃ perovskite solar cell, achieving the champion PCE of 23.23% for PSCs and 19.51% for 5 × 5 cm² mini-modules, meanwhile the enhanced T₈₀ lifetime of more than 3500 h at 40% relative humidity.

Abstract

FAPbI₃ perovskites have garnered considerable interest owing to their outstanding thermal stability, along with near-theoretical bandgap and efficiency. However, their inherent phase instability presents a substantial challenge to the long-term stability of devices. Herein, this issue through a dual-strategy of self-assembly 3D/0D quasi-core–shell structure is tackled as an internal encapsulation layer, and in situ introduction of excess PbI₂ for surface and grain boundary defects passivating, therefore preventing moisture intrusion into FAPbI₃ perovskite films. By utilizing this method alone, not only enhances the stability of the FAPbI₃ film but also effectively passivates defects and minimizes non-radiative recombination, ultimately yielding a champion device efficiency of 23.23%. Furthermore, the devices own better moisture resistance, exhibiting a T₈₀ lifetime exceeding 3500 h at 40% relative humidity (RH). Meanwhile, a 19.51% PCE of mini-module (5 × 5 cm²) is demonstrated. This research offers valuable insights and directions for the advancement of stable and highly efficient FAPbI₃ perovskite solar cells.

Pre-depositing an acceptor primer layer beneath the bulk-heterojunction layer results in higher acceptor phase continuity to facilitate electron collection. Surface doping preserves the thin primer layer from being completely removed during non-orthogonal solvent processing by slightly reducing its solubility. As a result, the primer layer remnant can constitute an acceptor-enriched bottom for a BHJ active layer and improve the domain orientation and size for efficient charge transport.

Abstract

In most non-fullerene organic solar cells comprising bulk-heterojunction active layers, the inter-domain connectivity of small-molecule acceptors is generally inferior to those of polymeric donors due to their intrinsic short-range ordering. This issue is even exacerbated by the physiochemical mismatch between acceptor-phases and metal-oxide electron transport layers in most inverted n-i-p devices, leading to inefficient electron collection. By pre-depositing an ultra-thin acceptor primer layer, it develops a novel acceptor-enriched-bottom active layer to reinforce the acceptor-phase continuity. It is however challenging to preserve the primer layer during non-orthogonal solvent processing. Thus, sequential n-type doping is implemented on the surface of the primer layer, which allows to slightly reduce the acceptor solubility by polarity regulation, as well as stabilize the film structure via strong π–π interaction between dopant/host acceptor. Upon acceptor enrichment, higher interfacial electron density enhances the built-in potential while the enlarged domains suppress both charge-transfer state and bimolecular recombination. Consequently, the champion device efficiency is greatly improved from ca. 16.1% to 18.0%, mainly resulting from the simultaneously elevated fill factor and short-circuit current density.

Three nonfused ring electron acceptors (3TT-C2-F, 3TT-C2-Cl, and 3TT-C2) are designed and synthesized with the concept of halogenation. Among them, the fluorinated acceptor 3TT-C2-F based devices can deliver the champion power conversion efficiency of over 17% due to enhanced the π–π stacking, improved the electron mobility, etc.

Abstract

Three nonfused ring electron acceptors (NFREAs), namely, 3TT-C2-F, 3TT-C2-Cl, and 3TT-C2, are purposefully designed and synthesized with the concept of halogenation. The incorporation of F or/and Cl atoms into the molecular structure (3TT-C2-F and 3TT-C2-Cl) enhances the π–π stacking, improves electron mobility, and regulates the nanofiber morphology of blend films, thus facilitating the exciton dissociation and charge transport. In particular, blend films based on D18:3TT-C2-F demonstrate a high charge mobility, an extended exciton diffusion distance, and a well-formed nanofiber network. These factors contribute to devices with a remarkable power conversion efficiency of 17.19%, surpassing that of 3TT-C2-Cl (16.17%) and 3TT-C2 (15.42%). To the best of knowledge, this represents the highest efficiency achieved in NFREA-based devices up to now. These results highlight the potential of halogenation in NFREAs as a promising approach to enhance the performance of organic solar cells.

Giant dimeric acceptors of Dimer-QX and Dimer-2CF are synthesized, without/with trifluoromethyl on quinoxaline core. Dimer-2CF exhibits stronger hetero-molecular interaction with donor, forming the smaller domains with ordered molecular packing and more favored vertical phase separation, thus promoting an efficiency of 19.02% and an FF of 80.03% with high stability in devices.

Abstract

Giant dimeric acceptor (G-Dimer) is becoming one of the most promising organic solar cell (OSC) materials because of its definite structure, long-term stability, and high efficiency. Strengthening the hetero-molecular interactions by monomer modification greatly influences the morphology and thus the device performance, but lacks investigation. Herein, two novel quinoxaline core-based G-Dimers, Dimer-QX and Dimer-2CF, are synthesized. By comparing trifluoromethyl-substituted Dimer-2CF and non-substituted Dimer-QX, the trifluoromethylation effect on the G-Dimer is investigated and revealed. The trifluoromethyl with strong electronegativity increases electrostatic potential and reduces surface energy of the G-Dimer, weakening the homo-molecular ordered packing but reinforcing the hetero-molecular interaction with the donor. The strong hetero-molecular interaction suppresses the fast assembly during the film formation, facilitating small domains with ordered molecular packing in the blend, which is a trade-off in conventional morphology control. Together with favorable vertical phase separation, efficient charge generation, and reduced bimolecular recombination are concurrently obtained. Hence, the Dimer-2CF-based OSCs obtain a cutting-edge efficiency of 19.02% with fill factor surpassing 80%, and an averaged extrapolated T ₈₀ of ≈12 000 h under continuous 80 °C heating. This study emphasizes the importance of hetero-molecular interaction and trifluoromethylation strategy, providing a facile strategy for designing highly efficient and stable OSC materials.

The effect of terminal groups on the different positions of spiro[fluorene-9,9′-xanthene]-diphenylamine is studied. SFX-3 exhibits apparent higher efficiency (22.42%) than other molecules in perovskite solar cells. SFX-3 also displays comparable efficiency, better device stability under different condition, and low synthesis cost compared to spiro-OMeTAD.

The molecular structures of hole-transporting materials (HTMs) have a significant effect on the performance of perovskite solar cells (PSCs). In this work, four small-molecular HTMs (SFX-1, SFX-2, SFX-3, and SFX-4) are prepared by regulating the substitution sites of terminal diphenylamine groups on the spiro[fluorene-9,9′-xanthene] core. As SFX-1 and SFX-2 are well-documented compounds, this article adopts the original publication's acronyms, referring to them as SFX-MeOTAD and HTM-FX′, respectively. It is found that the terminal substitution sites exhibit a noticeable effect on the molecular properties. Among these molecules, SFX-3, whose terminal groups are located at the 3,6-substitution site on the fluorene side of SFX, has high conductivity and hole mobility, and the highest occupied molecular orbital level matches well with the perovskite. SFX-3 also shows better film-forming properties and better hole extraction ability than the molecules with other substitution sites. Higher power conversion efficiency (PCE) in PSCs with SFX-3 is comparable to that of traditional spiro-OMeTAD, but SFX-3's synthesis cost is only about one-third that of spiro-OMeTAD. Furthermore, the device utilizing SFX-3 exhibits remarkable stability, surpassing that of spiro-OMeTAD. Notably, the champion PCE of SFX-3-based PSCs reached 22.42%, marking the highest reported efficiencies among HTMs with SFX as the core.

Interfacial treatments between perovskite active layers and charge-transporting layers are a ubiquitous approach to reduce energetic losses in spin-coated perovskite solar cells. Despite this, there have only been a handful of demonstrations of surface passivation via roll-to-roll compatible deposition technologies. It is demonstrated that the ultrasonic spray deposition of iso-butylammonium bromide dimensionally engineers and passivates the perovskite: hole-transporting layer interface.

Defect management in perovskite solar cells (PSCs) via surface passivation has become a cornerstone in maximizing both stability and solar-to-electrical power conversion efficiency (PCE) of devices by reducing defect densities and/or improving energetic alignment between the perovskite and charge-transporting layers. Despite this, few reports explore the use of roll-to-roll compatible technologies to deposit such interfacial treatments, limiting the applicability of passivation in real-world contexts. In this work, iso-butylammonium bromide (i-BABr) is spray-coated onto a Cs_0.15FA_0.85PbI_2.85Cl_0.15 perovskite surface which is deposited using gas-assisted ultrasonic spray coating. It is found that i-BABr treatments result in the formation of a quasi-2D perovskite layer. The spray-coated surface treatment results in an impressive 80 mV improvement in the median open-circuit voltage with respect to untreated devices. Importantly, the spray-coated passivation results in very similar positive benefits to the application of spin-coated treatments demonstrating the promise of the spray-passivation methodology. It is shown that devices created in this manner demonstrate PCEs of up to 21.0% (19.4% stabilized), representing the highest reported efficiency for one-step, spray-coated methylammonium-free PSCs. This work represents the first demonstration of a spray-coated surface passivation treatment that is compatible with high-throughput, roll-to-roll processing.

The single-glass encapsulation leads to thorough and homogeneous melting of the encapsulant, which alleviates the compression pressure on the perovskite solar cells during the lamination process alongwith minimized parasitic optical loss caused by the incomplete melted encapsulants. This strategy yields a nondestructive encapsulated device with exceptional stability and the underlying mechanism is explored through finite–element analysis and optical simulations.

Vacuum lamination encapsulation is widely adopted to prolong the duration of perovskite solar cells (PSCs) in real operation. However, additional encapsulant along with rigorous processing conditions leads to severe power conversion efficiency (PCE) loss to the corresponding devices. Herein, thermal and optical simulations and experiments are combined, to analyze the mechanisms for device failure during vacuum lamination. Single-glass encapsulation structure is proposed, which exhibits enhanced thermal conductivity, ensuring thorough and homogeneous melting of the encapsulant during the lamination process. This effectively mitigates delamination within the module and reduces parasitic photocurrent losses in the PSC device after encapsulation. Notably, the single-glass encapsulation devices retain 88% of their initial PCE after 1000 h damp heat test and successfully pass the thermal cycling standard (IEC 61 215:2016) with 95% retention of initial PCE after 250 cycles.

It has been found that doping naphthalimide-based molecules (NE or NDA) not only solves problems of ZnO aggregation and surface defects, but also enhances the ability of charge transfer and lowers the work function of the cathode in organic solar cells.

So far, the recombination center of photogenerated carriers caused by surface defects in ZnO results in poor thickness tolerance and inefficient charge extraction, severely limiting the performance and stability of inverted organic solar cells (OSCs). Therefore, hybrid cathode interfacial layers (CILs) are fabricated in devices by doping naphthalimide-based molecules (NE and NDA) into ZnO, and significantly improved performance and stability are achieved for all tested devices. It is found that doping NE or NDA not only solves the problems of ZnO aggregation and surface defects, but also enhances the ability of charge transfer and lowers the work function of cathode. As a result, the OSCs based on PM6:Y6 with ZnO:NE 1% as a CIL exhibit the highest power conversion efficiency (16.72%), which is better than that of pristine ZnO. The research shows that N atoms in naphthalimide react with Zn ions, and −NH bonds form noncovalent interaction with heteroatoms in the blend, which is conducive to the formation of better chemical bond in hybrid materials and providing more transfer channels for carriers. This study highlights a promising strategy for enhancing the performance of inverted OSCs by the hybrid CIL strategy.

Herein, an effective redox strategy is developed to improve the quality of perovskite film by incorporating 4-fluorobenzothiohydrazide (FBTH) into cesium lead triiodide (CsPbI₃) precursor solution. A new compound FBTH-I is obtained, which can passivate the Pb-related defects and restrain I⁻ migration. Consequently, FBTH-treated CsPbI₃ perovskite solar cell (PSC) achieves a distinguished PCE of 21.41% with an excellent V _oc of 1.231 V and an outstanding operational stability.

Abstract

To simultaneously stabilize cesium lead triiodide (CsPbI₃) precursor solution and passivate the defects in CsPbI₃ film is greatly significant for achieving highly stable and efficient CsPbI₃ perovskite solar cells (PSCs). Herein, an effective redox 4-fluorobenzothiohydrazide (FBTH) is developed to stabilize the precursor solution and passivate iodine/lead-related defects for high-quality CsPbI₃ film. The comprehensive research confirms that 1) a new compound FBTH-I is obtained from an effective redox interaction between FBTH and molecular iodine (I₂) in perovskite precursor solution, which can effectively impede the formation of I₂ molecule and restrain I⁻ migration in perovskite film by forming N–H···I bond; 2) FBTH-I can also passivate Pb-related defects via forming S···Pb interaction. Consequently, the CsPbI₃ PSC based on FBTH-treated precursor solution exhibits a fascinating power conversion efficiency (PCE) of 21.41%, which is one of the highest PCE values among the reported pure CsPbI₃ PSCs so far, and an outstanding stability against the harsh conditions, such as thermal annealing and continuous light-illumination.

The slow re-ordered stage in blend films facilitates better phase separation and proper grain size, while too strong interaction between the solvent and donor/acceptor materials leads to large grains and undesirable phase separation, which can seriously affect the photovoltaic properties in the blend film.

Abstract

Achieving high-performance in all-small-molecule organic solar cells (ASM-OSCs) significantly relies on precise nanoscale phase separation through domain size manipulation in the active layer. Nonetheless, for ASM-OSC systems, forging a clear connection between the tuning of domain size and the intricacies of phase separation proves to be a formidable challenge. This study investigates the intricate interplay between domain size adjustment and the creation of optimal phase separation morphology, crucial for ASM-OSCs’ performance. It is demonstrated that exceptional phase separation in ASM-OSCs’ active layer is achieved by meticulously controlling the continuity and uniformity of domains via re-packing process. A series of halogen-substituted solvents (Fluorobenzene, Chlorobenzene, Bromobenzene, and Iodobenzene) is adopted to tune the re-packing kinetics, the ASM-OSCs treated with CB exhibited an impressive 16.2% power conversion efficiency (PCE). The PCE enhancement can be attributed to the gradual crystallization process, promoting a smoothly interconnected and uniformly distributed domain size. This, in turn, leads to a favorable phase separation morphology, enhanced charge transfer, extended carrier lifetime, and consequently, reduced recombination of free charges. The findings emphasize the pivotal role of re-packing kinetics in achieving optimal phase separation in ASM-OSCs, offering valuable insights for designing high-performance ASM-OSCs fabrication strategies.

Herein, an electron transport layer ink is designed using hybrid fullerenes composed of mixed C₆₀, phenyl C₆₁ butyric acid methyl ester, and indene-C₆₀ bisadduct. This electron transport layer exhibits high conductivity, good energy-level alignment, and low interfacial nonradiative recombination. The all-perovskite tandem solar modules achieve a champion power conversion efficiency of 23.3% (aperture area = 20.25 cm²).

Abstract

All-perovskite tandem solar cells offer the potential to surpass the Shockley–Queisser (SQ) limit efficiency of single-junction solar cells while maintaining the advantages of low-cost and high-productivity solution processing. However, scalable solution processing of electron transport layer (ETL) in p-i-n structured perovskite solar subcells remains challenging due to the rough perovskite film surface and energy level mismatch between ETL and perovskites. Here, scalable solution processing of hybrid fullerenes (HF) with blade-coating on both wide-bandgap (≈1.80 eV) and narrow-bandgap (≈1.25 eV) perovskite films in all-perovskite tandem solar modules is developed. The HF, comprising a mixture of fullerene (C₆₀), phenyl C₆₁ butyric acid methyl ester, and indene-C₆₀ bisadduct, exhibits improved conductivity, superior energy level alignment with both wide- and narrow-bandgap perovskites, and reduced interfacial nonradiative recombination when compared to the conventional thermal-evaporated C₆₀. With scalable solution-processed HF as the ETLs, the all-perovskite tandem solar modules achieve a champion power conversion efficiency of 23.3% (aperture area = 20.25 cm²). This study paves the way to all-solution processing of low-cost and high-efficiency all-perovskite tandem solar modules in the future.

W e present a new 1.80 eV wide-bandgap (WBG) perovskite treated with piperazinium iodide (PI) for all-perovskite tandem solar cells. This treatment eliminates non-radiative recombination losses and reduces defect density resulting in an open circuit voltage of 1.36 V and enhanced photostability. Combined with a narrow bandgap (NBG) perovskite, this enables a tandem cell with a certified scan efficiency of 27.5%.

Abstract

All-perovskite tandem solar cells show great potential to enable the highest performance at reasonable costs for a viable market entry in the near future. In particular, wide-bandgap (WBG) perovskites with higher open-circuit voltage (V _OC) are essential to further improve the tandem solar cells’ performance. Here, a new 1.8 eV bandgap triple-halide perovskite composition in conjunction with a piperazinium iodide (PI) surface treatment is developed. With structural analysis, it is found that the PI modifies the surface through a reduction of excess lead iodide in the perovskite and additionally penetrates the bulk. Constant light-induced magneto-transport measurements are applied to separately resolve charge carrier properties of electrons and holes. These measurements reveal a reduced deep trap state density, and improved steady-state carrier lifetime (factor 2.6) and diffusion lengths (factor 1.6). As a result, WBG PSCs achieve 1.36 V V _OC, reaching 90% of the radiative limit. Combined with a 1.26 eV narrow bandgap (NBG) perovskite with a rubidium iodide additive, this enables a tandem cell with a certified scan efficiency of 27.5%.

A novel pyrene-fused dimerized acceptor has been synthesized to show extended π-conjugation, low solubility, high glass transition temperature, and low-lying frontier energy levels, leading to over 19% efficiency and highly stable ternary organic solar cells.

Abstract

A pyrene-fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive “butterfly-like” structure, comprising two Y-acceptors as wings fused with a pyrene-based backbone. The extended π-conjugated backbone and the electron-donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (T _g), and low-lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non-radiative voltage loss, and elevating open-circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high T _g exhibited by the pyrene-fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal-treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the “butterfly-like” design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs.

Sufficient conversion of residual photoinstable PbI₂ into robust 1D perovskite (EMIMPbI₃) can improve device stability, while the formation of an interfacial dipole layer at the SnO₂/perovskite interface can reduce the energetic mismatch via a single process. The optimized device delivers an efficiency of 24.28 % and a remarkable open circuit voltage of 1.19 V, accompanied with excellent humidity and operational stability.

Abstract

Eliminating the undesired photoinstability of excess lead iodide (PbI₂) in the perovskite film and reducing the energy mismatch between the perovskite layer and heterogeneous interfaces are urgent issues to be addressed in the preparation of perovskite solar cells (PVSCs) by two-step sequential deposition method. Here, the 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) is employed to convert superfluous PbI₂ to more robust 1D EMIMPbI₃ which can withstand lattice strain, while forming an interfacial dipole layer at the SnO₂/perovskite interface to reconfigure the interfacial energy band structure and accelerate the charge extraction. Consequently, the unencapsulated PVSCs device attains a champion efficiency of 24.28 % with one of the highest open-circuit voltage (1.19 V). Moreover, the unencapsulated devices showcase significantly improved thermal stability, enhanced environmental stability and remarkable operational stability accompanied by 85 % of primitive efficiency retained over 1500 h at maximum power point tracking under continuous illumination.

Nature Energy, Published online: 20 November 2023; doi:10.1038/s41560-023-01383-9

Efficient and stable lead-free tin perovskite solar cells are developed by modifying the buried interface between perovskite and NiO _x via self-assembled monolayer molecule (4-(7H-dibenzo[c,g]carbazol-7-yl)ethyl)phosphonic acid, which achieve a record power conversion efficiency of 14.19% for small-area device and 12.05% for large-area (1 cm²) device.

Abstract

Inorganic nickel oxide (NiO _x ) is an ideal hole transport material (HTM) for the fabrication of high-efficiency, stable, and large-area perovskite photovoltaic devices because of its low cost, stability, and ease of solution processing. However, it delivers low power conversion efficiency (PCE) in tin perovskite solar cells (TPSCs) compared to other organic HTMs. Here, the origin of hole transport barriers at the perovskite–NiO _x interface is identified and a self-assembled monolayer interface modification is developed, through introducing (4-(7H-dibenzo[c,g]carbazol-7-yl)ethyl)phosphonic acid (2PADBC) into the perovskite–NiO _x interface. The 2PADBC anchors undercoordinated Ni cations through phosphonic acid groups, suppressing the reaction of highly active Ni^≥3+ defects with perovskites, while increasing the electron density and oxidation activation energy of Sn at the perovskite interface, reducing the interface nonradiative recombination caused by tetravalent Sn defects. The devices deliver significantly increased open-circuit voltage from 0.712 to 0.825 V, boosting the PCE to 14.19% for the small-area device and 12.05% for the large-area (1 cm²) device. In addition, the 2PADBC modification enhances the operational stability of NiO _x -based TPSCs, maintaining more than 93% of their initial efficiency after 1000 h.

Nature Energy, Published online: 16 November 2023; doi:10.1038/s41560-023-01406-5