Chen Weijie

For printable mesoscopic perovskite solar cells, bidentate passivation (BP) is an important approach to enhance their photovoltaic performance. Here, the competition mechanism is discovered between the chlorine atom of the multidentate molecule 6-CP and the adjacent nitrogen atoms in the imidazole and pyrimidine rings. By utilizing the bidentate coordination between the chlorine atom and the nitrogen atom in the imidazole unit, the power conversion efficiency (PCE) is increased of the pristine sample from 16.25% to 17.63%. The formation of BP enhances the interface hole selectivity and charge transfer, suppresses nonradiative recombination, and improves the device stability under high humidity conditions.

Abstract

For metal halide perovskite solar cells, bidentate passivation (BP) is highly effective, but currently, only passivation sites rather than molecular environments are being considered. Here, the authors report an effective approach for high-performance fully printable mesoscopic perovskite solar cells (FP-PSCs) through the BP strategy using the multidentate molecule 6-chloropurine (6-CP). By utilizing density functional theory (DFT) calculations, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) characterizations, the competition mechanism is identified of BP between the chlorine atom and neighboring nitrogen atom of the imidazole and pyrimidine rings. Through BP between the chlorine atom and adjacent nitrogen atom in imidazole, the power conversion efficiency (PCE) of the pristine samples is significantly enhanced from 16.25% to 17.63% with 6-CP. The formation of BP enhances interfacial hole selectivity and charge transfer, and suppresses nonradiative recombination, improving device stability under high humidity conditions. The competition mechanism of BP between two aromatic cycles provides a path for designing molecular passivants and selecting passivation pathways to approach theoretical limits.

A new non-halogenated solvent additive, 9-fluorenone (9-FL), is utilized to effectively optimize the morphology of the photoactive layer, mainly due to the enhanced thermal-assisted molecular reorganization upon volatilization of the additive. Consequently, efficient and symmetric charge transport and suppressed photo-induced trap generation are obtained, resulting in halogen-free solvent-processed organic photovoltaic cells with remarkably high efficiencies and significantly extended lifetime.

Abstract

Achieving environmentally friendly solvent-processed high-performance organic photovoltaic cells (OPVs) is a crucial step toward their commercialization. Currently, OPVs with competitive efficiencies rely heavily on harmful halogenated solvent additives. Herein, the green and low-cost 9-fluorenone (9-FL) is employed as a solid additive. By using the o-xylene/9-FL solvent system, the PM6:BTP-eC9-based devices deliver power-conversion efficiencies of 18.6% and 17.9% via spin-coating and blade-coating respectively, outperforming all PM6:Y-series binary devices with green solvents. It is found that the addition of 9-FL can regulate the molecular assembly of both PM6 and BTP-eC9 in film-formation (molecule-level mixing) and post-annealing (thermal-assisted molecular reorganization with additive volatilization) stages, so as to optimize the blend morphology. As a result, the charge transport ability of donor and acceptor phases are simultaneously enhanced, and the trap-assisted recombination is reduced, which contributes to the higher short-circuit current density and fill factor. Moreover, the generation of photo-induced traps is significantly suppressed, resulting in improved stability under illumination. It is further demonstrated the excellent universality of 9-FL in various photoactive systems, making it a promising strategy to advance the development of eco-friendly OPVs.

Efficient doping of hybrid perovskites holds the potential to further advance solar cell efficiency. This study presents a generic strategy for perovskite doping by constructing ultra-shallow near-edge states. These states can effectively prolong electron-hole recombination through efficient trap and de-trap processes, resulting in over 25% efficiency in inverted perovskite solar cells with superior long-term operational stability.

Abstract

Electronic band structure engineering of metal-halide perovskites (MHP) lies at the core of fundamental materials research and photovoltaic applications. However, reconfiguring the band structures in MHP for optimized electronic properties remains challenging. This article reports a generic strategy for constructing near-edge states to improve carrier properties, leading to enhanced device performances. The near-edge states are designed around the valence band edge using theoretical prediction and constructed through tailored material engineering. These states are experimentally revealed with activation energies of around 23 milli-electron volts by temperature-dependent time-resolved spectroscopy. Such small activation energies enable prolonged carrier lifetime with efficient carrier transition dynamics and low non-radiative recombination losses, as corroborated by the millisecond lifetimes of microwave conductivity. By constructing near-edge states in positive-intrinsic-negative inverted cells, a champion efficiency of 25.4% (25.0% certified) for a 0.07-cm² cell and 23.6% (22.7% certified) for a 1-cm² cell is achieved. The most stable encapsulated cell retains 90% of its initial efficiency after 1100 h of maximum power point tracking under one sun illumination (100 mW cm⁻²) at 65 °C in ambient air.

The integration of ANT into the CsPbI₂Br perovskite precursor serves multiple beneficial functions: it slows down the crystallization process and passivates uncoordinated Pb²⁺ dangling bonds, as well as antisite defects (PbI₃ ⁻). This contributes to the formation of high-quality CsPbI₂Br perovskite, ultimately enhancing the photovoltaic performance of perovskite solar cells.

All-inorganic CsPbI₂Br mixed halide perovskites show promise as wide-bandgap photoabsorbers in photovoltaics. However, the rapid crystal growth observed in solution-processed CsPbI₂Br often leads to morphologies plagued by pinholes and defects, which limit device performance. This study introduces 2-Amino-5-nitrothiazole (ANT), an innovative precursor additive, to enhance film quality. ANT's selective interactions with the perovskite precursor moderate the crystal growth, resulting in a dense, flawless CsPbI₂Br film characterized by superior crystallinity and coverage. Furthermore, the NH₂ group in ANT coordinates with Pb octahedra, effectively mitigating charge defects through NHI/Br bonds. Simultaneously, SCN sites interact with uncoordinated Pb²⁺ ions, reducing defect states and nonradiative recombination. This innovation achieves an impressive device efficiency of 17.13% with a fill factor (FF) of 83.41%, surpassing the control's efficiency of 15.21% (FF of 80.45%). Notably, the champion device maintains an efficiency of 29.47% under indoor light-emitting diode lighting at 1000 lux. Additionally, the optimized perovskite solar cell demonstrates remarkable stability, retaining ≈90% of its efficiency for over 720 h at 85 °C in air, even without encapsulation.

Three isomeric perhalogenated thiophenes were reported as solid additives to optimize the morphological characters of all-polymer organic solar cells (APSCs). Among them, power conversion efficiency over 18 % and long-term thermal stability (T ₉₀ lifetime is 550 hours) were realized for SA-T1-treated binary APSC, providing a possibility for obtaining high-performance APSCs.

Abstract

Morphological control of all-polymer blends is quintessential yet challenging in fabricating high-performance organic solar cells. Recently, solid additives (SAs) have been approved to be capable in tuning the morphology of polymer: small-molecule blends improving the performance and stability of devices. Herein, three perhalogenated thiophenes, which are 3,4-dibromo-2,5-diiodothiophene (SA-T1), 2,5-dibromo-3,4-diiodothiophene (SA-T2), and 2,3-dibromo-4,5-diiodothiophene (SA-T3), were adopted as SAs to optimize the performance of all-polymer organic solar cells (APSCs). For the blend of PM6 and PY-IT, benefitting from the intermolecular interactions between perhalogenated thiophenes and polymers, the molecular packing properties could be finely regulated after introducing these SAs. In situ UV/Vis measurement revealed that these SAs could assist morphological character evolution in the all-polymer blend, leading to their optimal morphologies. Compared to the as-cast device of PM6 : PY-IT, all SA-treated binary devices displayed enhanced power conversion efficiencies of 17.4–18.3 % with obviously elevated short-circuit current densities and fill factors. To our knowledge, the PCE of 18.3 % for SA-T1-treated binary ranks the highest among all binary APSCs to date. Meanwhile, the universality of SA-T1 in other all-polymer blends is demonstrated with unanimously improved device performance. This work provide a new pathway in realizing high-performance APSCs.

The surface contamination issue of solution-grown perovskite single crystals is addressed by the self-cleaning effect induced by an amphiphilic molecule, which leads to improved crystal properties and a record efficiency of 23.4 % for single-crystal perovskite solar cells. Moreover, this strategy applies to perovskite single crystals with different morphologies and compositions, which can contribute to improve other optoelectronic devices.

Abstract

Metal halide perovskite single crystals are promising for diverse optoelectronic applications. As a universal issue of solution-grown perovskite single crystals, surface contamination causes adverse effect on material properties and device performance. Herein, learning from the self-cleaning effect of lotus leaf, we address the surface contamination issue by introducing an amphiphilic long-chain organic amine into the perovskite crystal growth solution. Self-assembly of CTAC provides a hydrophobic crystal surface, inducing spontaneous removal of residual growth solution, which results in clean surface and better optoelectronic properties of perovskite single crystals. An impressive efficiency of 23.4 % is obtained, setting a new record for FA_xMA_1-xPbI₃ single-crystal perovskite solar cells (PSCs). Moreover, our strategy also applies to perovskite single crystals with different morphology and composition, which may contribute to improvement of other single-crystal perovskite optoelectronic devices.

Nature Energy, Published online: 04 January 2024; doi:10.1038/s41560-023-01421-6

A new star-shaped trimer acceptor (TYT-S) is developed. The organic solar cells (OSCs) using TYT-S exhibit a high power conversion efficiency (PCE) of 19.0% and long-term stability, as well as excellent mechanical robustness (crack-onset strain = 21.6%). Consequently, intrinsically stretchable OSCs using TYT-S achieve high PCE and device stretchability at the same time, highlighting great potential for wearable applications.

Abstract

High power conversion efficiency (PCE), long-term stability, and mechanical robustness are prerequisites for the commercial applications of organic solar cells (OSCs). In this study, a new star-shaped trimer acceptor (TYT-S) is developed and high-performance OSCs with a PCE of 19.0%, high photo-stability (t _80% lifetime = 2600 h under 1-sun illumination), and mechanical robustness with a crack-onset strain (COS) of 21.6% are achieved. The isotropic molecular structure of TYT-S affords efficient multi-directional charge transport and high electron mobility. Furthermore, its amorphous structure prevents the formation of brittle crystal-to-crystal interfaces, significantly enhancing the mechanical properties of the OSC. As a result, the TYT-S-based OSCs demonstrate a significantly higher PCE (19.0%) and stretchability (COS = 21.6%) than the linear-shaped trimer acceptor (TYT-L)-based OSCs (PCE = 17.5% and COS = 6.4%) and the small-molecule acceptor (MYT)-based OSCs (PCE = 16.5% and COS = 1.3%). In addition, the increased molecular size of TYT-S, relative to that of MYT and dimer (DYT), suppresses the diffusion kinetics of the acceptor molecules, substantially improving the photostability of the OSCs. Finally, to effectively demonstrate the potential of TYT-S, intrinsically stretchable (IS)-OSCs are constructed. The TYT-S-based IS-OSCs exhibit high device stretchability (strain at PCE_80% = 31%) and PCE of 14.4%.

Here, Ph-4PACz is designed and synthesized to achieve a stronger interface dipole layer and suitable energy level alignment, meanwhile, aluminum oxide nanoparticles (Al₂O₃-NPs) are introduced to enhance the substrate flatness and self-assembled monolayer (SAM) coverage, resulting in a conformal perovskite film with minimal gaps and energy loss at the buried interface. Hence, excellent performance is obtained in large-area devices.

Abstract

The efficiency loss caused by area scaling is one of the key factors hindering the industrial development of perovskite solar cells. The energy loss and contact issues in the buried interface are the main reasons. Here, a new self-assembled monolayer (SAM), Ph-4PACz, with a large dipole moment (2.32 D) is obtained . It is found that Ph-4PACz with high polarity can improve the band alignment and minimize the energy loss , resulting in an open-circuit voltage (V _oc) as high as 1.2 V for 1.55 eV perovskite. However, when applied to large-area devices, the fill factor (FF) still suffered from significant attenuation. Therefore, alumina nanoparticles (Al₂O₃-NPs) are introduced to the interface between Ph-4PACz and rough FTO substrate to further improve the flatness , resulting in a conformal perovskite film with almost no voids in the buried interface, thus promoting low exciton binding energy, fast hot-carrier extraction and low non-radiative recombination. The final devices achieved a small-area power conversion efficiency (PCE) of 25.60% and a large-area (1 cm²) PCE of 24.61% (certified at 24.48%), which represents one of the highest PCE for single device ≥ 1 cm² area. Additionally, mini-modules and stability testing are also carried out to demonstrate the feasibility of commercialization.

Blade-coated wide-bandgap perovskites encounter top–down inhomogeneity strains. Utilizing mixed-cation post-treatment for strain relief, large-area wide-bandgap solar cells demonstrate enhanced efficiency and stability. Specifically, 1 cm²-area 1.77 eV-bandgap cells achieve an 18.71% efficiency (stabilized at 18.50%), while 4-terminal all-perovskite tandems reach an exceptional 27.64% efficiency, coupled with enhanced stability.

Abstract

The realization of efficient large-area perovskite solar cells stands as a pivotal milestone for propelling their future commercial viability. However, the upscaling fabrication of perovskite solar cells is hampered by efficiency losses, and the underlying growth mechanism remains enigmatic. Here, it is unveiled that a prevalent upscaling technology, namely blade-coating, inherently triggers top-down inhomogeneity strains, predominantly concentrated on the surface of wide-bandgap perovskite films. Through strain mitigation strategies, the perovskite films exhibit reduced halide vacancies, leading to enhanced stability and improved optoelectronic characteristics. Consequently, the blade-coated perovskite solar cells achieve minimal efficiency loss when transitioning from small-area to large-area devices, enabling the realization of 1 cm²-area 1.77 eV-bandgap cells with a remarkable efficiency of 18.71%. Additionally, the strain-relieved device exhibits an exceptional 109% retention of its initial efficiency even after 400 h of continuous operation, in stark contrast to the control device which experiences a decline to 91%. Furthermore, the resulting 4-terminal all-perovskite tandem solar cells crafted utilizing blade-coated 1.77 eV-bandgap subcells achieve a maximum efficiency of 27.64% (stabilized at 27.28%). This study not only sheds light on the intricacies of upscaling preparation techniques but also overcomes potential obstacles that can impede the trajectory toward achieving large-scale perovskite solar cells.

The exciton utilization near the cathode of LbL OPVs is still challenging due to the restricted diffusion distance of excitons. By incorporating less PM1 into the L8-BO layer, an optimal PCE of 18.81% can be achieved benefiting from more efficient exciton separation in the L8-BO layer near the cathode, as well as more ordered molecular arrangement for charge transport and collection.

Abstract

The layer-by-layer (LbL) organic photovoltaics (OPVs) are constructed with wide-bandgap donor PM1 and narrow-bandgap acceptor L8-BO. The exciton utilization near cathode is still challenging considering restricted diffusion distance of excitons and inability for transferring energy from L8-BO to PM1. Herein, donor incorporation into acceptor layer (DIA) strategy is employed to improve exciton utilization near cathode. The efficiency of LbL OPVs can be improved from 18.02% to 18.81% by incorporating 10 wt% PM1 into L8-BO layer, which is closely associated with efficient exciton separation into L8-BO layer originated from more adequate donor/acceptor interface for faster charge transfer, as evidenced by magneto-photocurrent and transient absorption results. The in situ test and morphological characterization clarify that molecular packing property can be improved benefited from prolonged aggregation and nucleation time of acceptor layer assisted by DIA strategy, contributing to more efficient charge transport and inhibited charge recombination in active layers. The thickness insensitive property of LbL OPVs can be also improved induced by DIA strategy, indicated by PCE retention value (82.2% vs. 74.0%) for PM1/L8-BO:PM1 and PM1/L8-BO OPVs when acceptor layer thickness increased to ≈180 nm. This work demonstrates the effectiveness of DIA strategy in improving efficiency and thickness tolerance of LbL OPVs.

Two dipole spacers based on azetidine (Az), namely 3-OHAz and 3,3-DFAz, were developed for 2D PSCs. The 3,3-DFAz-Pb (n=4) with highly polarized dipole and fluorinated spacers exhibits improved film quality, better-matched energy level alignment, and a lower exciton binding energy compared to 3-OHAz-Pb film. When using mixed A-site cations, the 3,3-DFAz-based device achieved a champion PCE of 19.85 %.

Abstract

Layered two-dimensional (2D) perovskites are emerging as promising optoelectronic materials owing to their excellent environmental stability. Regulating the dipole moment of organic spacers has the potential to reduce the exciton binding energy (E _b) of 2D perovskites and improve their photovoltaic performance. Here, we developed two azetidine-based secondary ammonium spacers with different electron-withdrawing groups, namely 3-hydroxyazatidine (3-OHAz) and 3,3-difluoroazetidine (3,3-DFAz) spacers, for 2D Ruddlesden-Popper (RP) perovskites. It was found that the large dipole moment of the fluorinated dipole spacer could effectively enhance the interaction between organic spacers and inorganic layers, leading to improved charge dissociation in 2D RP perovskite. In contrast to 3-OHAz spacer, the 2D perovskite using 3,3-DFAz as spacer also shows improved film quality, optimized energy level alignment, and reduced exciton binding energy. As a result, the 2D perovskite (n=4) device based on 3,3-DFAz yields an outstanding efficiency of 19.28 %, surpassing that of the 3-OHAz-Pb device (PCE=11.35 %). The efficiency was further improved to 19.85 % when using mixed A-site cation of MA_0.95FA_0.05. This work provides an effective strategy for modulating the energy level alignment and reducing the E _b by regulating the dipole moment of organic spacers, ultimately enabling the development of high-performance 2D perovskite solar cells.

In this study, we introduce trimethoxy (3,3,3-trifluoropropyl)-silane (F₃-TMOS) with molecular dipole moment pointing towards the hole transport layer as the buried interface modification material, which not only optimizes energy level alignment and carrier dynamics but also relieves interface strain and reduces lattice distortion, resulting in a champion power conversion efficiency (PCE) of 14.67 %.

Abstract

Buried interface modification can effectively improve the compatibility between interfaces. Given the distinct interface selections in perovskite solar cells (PSCs), the applicability of a singular modification material remains limited. Consequently, in response to this challenge, we devised a tailored molecular strategy based on the electronic effects of specific functional groups. Therefore, we prepared three distinct silane coupling agents, and due to the varying inductive effects of these functional groups, the electronic distribution and molecular dipole moments of the coupling agents are correspondingly altered. Among them, trimethoxy (3,3,3-trifluoropropyl)-silane (F₃-TMOS), which possesses electron-withdrawing groups, generates a molecular dipole moment directed toward the hole transport layer (HTL). This approach changes the work function of the HTL, optimizes the energy level alignment, reduces the open-circuit voltage loss, and facilitates carrier transport. Furthermore, through the buffering effect of the coupling agent, the interface strain and lattice distortion caused by annealing the perovskite are reduced, enhancing the stability of the tin-based perovskite. Encouragingly, tin PSCs treated with F₃-TMOS achieved a champion efficiency of 14.67 %. This strategy provides an expedient avenue for the design of buried interface modification materials, enabling precise molecular adjustments in accordance with distinct interfacial contexts to ameliorate mismatched energetics and enhance carrier dynamics.

We developed four small-molecule acceptors (Qo1, Qo2, Qo3 and Qo4) by incorporating a methylation strategy. Solar cells fabricated with polymer donor PM6 and Qo2 realized the highest power conversion efficiency of 18.4 %, surpassing the efficiencies of devices based on Qo1 (15.8 %), Qo3 (16.7 %), and Qo4 (2.4 %).

Abstract

Utilizing intermolecular hydrogen-bonding interactions stands for an effective approach in advancing the efficiency and stability of small-molecule acceptors (SMAs) for polymer solar cells. Herein, we synthesized three SMAs (Qo1, Qo2, and Qo3) using indeno[1,2-b]quinoxalin-11-one (Qox) as the electron-deficient group, with the incorporation of a methylation strategy. Through crystallographic analysis, it is observed that two Qox-based methylated acceptors (Qo2 and Qo3) exhibit multiple hydrogen bond-assisted 3D network transport structures, in contrast to the 2D transport structure observed in gem-dichlorinated counterpart (Qo4). Notably, Qo2 exhibits multiple and stronger hydrogen-bonding interactions compared with Qo3. Consequently, PM6 : Qo2 device realizes the highest power conversion efficiency (PCE) of 18.4 %, surpassing the efficiencies of devices based on Qo1 (15.8 %), Qo3 (16.7 %), and Qo4 (2.4 %). This remarkable PCE in PM6 : Qo2 device can be primarily ascribed to the enhanced donor-acceptor miscibility, more favorable medium structure, and more efficient charge transfer and collection behavior. Moreover, the PM6 : Qo2 device demonstrates exceptional thermal stability, retaining 82.8 % of its initial PCE after undergoing annealing at 65 °C for 250 hours. Our research showcases that precise methylation, particularly targeting the formation of intermolecular hydrogen-bonding interactions to tune crystal packing patterns, represents a promising strategy in the molecular design of efficient and stable SMAs.

Publication date: March 2024

Source: Nano Energy, Volume 121

Author(s): Yapeng Sun, Jiankai Zhang, Bo Yu, Shengwei Shi, Huangzhong Yu

For achieving highly efficient and stable perovskite/silicon tandem solar cells on the fully-textured silicon substrate, triple-functional 2-fluoroisonicotinic acid (2-FNA) is used as passivator in the perovskite. 2-FNA can efficiently suppress non-radiative recombination and aid in the formation of better interfacial contact between perovskite and C₆₀ layers, eventually leading to a top power conversion efficiency of 28.6%.

Abstract

Perovskite/silicon tandem solar cells (TSCs) have aroused much attentions in recent years. One of keys for achieving highly efficient and stable TSCs is to guarantee effective charge transfer, especially on the rough textured silicon substrate due to the poor adhesion between interlayers. Here, a 2-fluoroisonicotinic acid (2-FNA) additive that possesses fluorine (-F), carboxylic acid (-COOH), and pyridine nitrogen as functional groups in the perovskite precursor to assist the crystallization process is utilized. It shows that 2-FNA can efficiently reduce the defects and suppress non-radiative recombination of perovskite layers by bonding with the uncoordinated Pb²⁺ ions, formamidinium (FA⁺), and halide vacancies, leading to notably prolonged carrier lifetime. Most importantly, this found that 2-FNA aids in the formation of better interfacial contact between the perovskite and C₆₀ layer on top, thus enhancing the interfacial electron extraction therein, eventually leading to an increased power conversion efficiency (PCE) of 28.61% on champion perovskite/silicon TSCs from 27.08% on control counterparts. This work provides a practical route to further advance the PV performance and applicability of perovskite/silicon TSCs.

Pb–Sn-based inorganic perovskite solar cells with a record efficiency of 17.12% are achieved via B-site Mn co-doping strategy and introducing benzhydroxamic acid (BHA) as multifunctional additive. Mn-doping contributes to structurally stable inorganic perovskite. While, BHA additive mitigates Sn²⁺ oxidation, and passivates Sn(II) related defects, forming an in situ encapsulation of the perovskite.

Abstract

Pb–Sn mixed inorganic perovskite solar cells (PSCs) have garnered increasing interest as a viable solution to mitigate the thermal instability and lead toxicity of hybrid lead-based PSCs. However, the relatively poor structural stability and low device efficiency hinder its further development. Herein, high-performance manganese (Mn)-doped Pb–Sn–Mn-based inorganic perovskite solar cells (PSCs) are successfully developed by introducing Benzhydroxamic Acid (BHA) as multifunctional additive. The incorporation of smaller divalent Mn cations contributes to a contraction of the perovskite crystal, leading to an improvement in structural stability. The BHA additive containing a reductive hydroxamic acid group (O═C–NHOH) not only mitigates the notorious oxidation of Sn²⁺ but also interacts with metal ions at the B-site and passivates related defects. This results in films with high crystallinity and low defect density. Moreover, the BHA molecules tend to introduce a near-vertical dipole moment that parallels the built-in electric field, thus facilitating charge carrier extraction. Consequently, the resulting device delivers a champion PCE as high as 17.12%, which represents the highest reported efficiency for Pb–Sn-based inorganic PSCs thus far. Furthermore, the BHA molecule provides an in situ encapsulation of the perovskite grain boundary, resulting in significant enhancement of device air stability.

Publication date: 17 January 2024

Source: Joule, Volume 8, Issue 1

Author(s): Fuzong Xu, Erkan Aydin, Jiang Liu, Esma Ugur, George T. Harrison, Lujia Xu, Badri Vishal, Bumin K. Yildirim, Mingcong Wang, Roshan Ali, Anand S. Subbiah, Aren Yazmaciyan, Shynggys Zhumagali, Wenbo Yan, Yajun Gao, Zhaoning Song, Chongwen Li, Sheng Fu, Bin Chen, Atteq ur Rehman

4-Fluoro aniline hydroiodide is used to enhance the SnO₂ properties. Fluorine helps in altering the energy levels of SnO₂ while, aniline groups aid defect passivation at the perovskite|SnO₂ interface. The modified surface is probed for surface energy, crystallization onset changes along withcharge extraction mechanisms at SnO₂|FACs interfaces. Carbon-based perovskite solar cells with the modified SnO₂ render efficiency >15.6%.

SnO₂ is a widely used electron-transporting layer (ETL) in perovskite solar cells. Despite the high compatibility with the perovskite absorber layers, the presence of traps at the perovskite|SnO₂ interface results in performance losses; hence, their modification to improve the performance and stability of perovskite solar cells (PSCs) is therefore important. Herein, the SnO₂ ETL is enhanced by incorporating a bifunctional aromatic amino fluorine molecule into the SnO₂ precursor solution. The fluorine molecule is found to partially substitute the Sn and alter the energy levels while the aniline group aids in regulating the nucleation/growth rate of the perovskite crystalline films. Herein, a hole transporting material-free carbon-based PSCs (CPSCs) is fabricated. It is found that perovskite absorber layers deposited on these modified SnO₂ hybrid layers have higher optoelectronic quality, resulting in enhanced photovoltaic performance, device stability, and reduced hysteresis in CPSCs. Devices made with the modified hybrid SnO₂ layers exhibit power conversion efficiencies of 15.6% significantly better than unmodified SnO₂ with 13.5%. CPSCs with these modified SnO₂ films also exhibit remarkable retention of 88.7% of their initial PCE for a shelf-life period (ISOS-D1I) exceeding 1200 h.

A strategy of passivating dipole layer to reconstruct an efficient 3D/2D perovskite heterojunction has been successfully developed, enabling high-performance p-i-n perovskite solar cells.

Abstract

Constructing 3D/2D perovskite heterojunction is a promising approach to integrate the benefits of high efficiency and superior stability in perovskite solar cells (PSCs). However, in contrast to n-i-p architectural PSCs, the p-i-n PSCs with 3D/2D heterojunction have serious limitations in achieving high-performance as they suffer from a large energetic mismatch and electron extraction energy barrier from a 3D perovskite layer to a 2D perovskite layer, and serious nonradiative recombination at the heterojunction. Here a strategy of incorporating a thin passivating dipole layer (PDL) onto 3D perovskite and then depositing 2D perovskite without dissolving the underlying layer to form an efficient 3D/PDL/2D heterojunction is developed. It is revealed that PDL regulates the energy level alignment with the appearance of interfacial dipole and strongly interacts with 3D perovskite through covalent bonds, which eliminate the energetic mismatch, reduce the surface defects, suppress the nonradiative recombination, and thus accelerate the charge extraction at such electron-selective contact. As a result, it is reported that the 3D/PDL/2D junction p-i-n PSCs present a power conversion efficiency of 24.85% with robust stability, which is comparable to the state-of-the-art efficiency of the 3D/2D junction n-i-p devices.

Two functional 2D polymers with lead anchoring groups, namely, 2DP-BT and 2DP-Por, are synthesized. The 2D polymer (2DP-Por) exhibits matched energy levels and excellent defect passivation properties. A high efficiency of 24.12% has been demonstrated when 2DP-Por is used as a functional interfacial layer in perovskite solar cells, coupled with dramatically improved stability.

The hygroscopic dopants used in Spiro-OMeTAD hole-transport materials (HTMs) in n–i–p perovskite solar cells (PSCs) inevitably cause device degradation. Herein, two polymer interface materials based on lead anchoring groups are developed. It is found that 2D polymers 2DP-BT and 2DP-Por can form dense films and exhibit excellent hydrophobicity. Importantly, 2DP-Por can passivate the surface defects through noncovalent interactions, reducing nonradiative recombination loss. After introducing these polymer interface materials between the perovskite layer and the HTM layer, the optimized devices using 2DP-Por and 2DP-BT achieve champion power conversion efficiency of 24.12% and 23.29%, respectively, and the stability is significantly improved. These results indicate that developing polymer interface materials containing lead anchoring groups can improve PSC efficiency and stability and elucidate critical molecular design rules for interface materials.

A new, room-temperature-processed (RTP) Zn₂SnO₄ (ZSO) electron-transport layer (ETL) is developed to fabricate efficient all RTP perovskite solar cells (PSCs). The RTP-PSCs show high efficiency of 21.06% with almost no hysteresis, which are the best efficiencies reported to date for all RTP-PSCs. This work demonstrates that ZSO is an appropriate ETL for high-efficiency RTP-PSCs.

Room-temperature-processed (RTP) electron-transport layer (ETL) is a prerequisite for fabricating fully RTP perovskite solar cells (PSCs). Herein, an RTP-Zn₂SnO₄ (ZSO) ETL is deposited for achieving RTP-PSCs by magnetron sputtering using ZnO and SnO₂ targets. The ZSO ETL exhibits great electrical properties, better band alignment, and yields increased grain size of the perovskite grown on it, thus facilitating electron extraction from the perovskite layer to the ETL. As a result, a champion power conversion efficiency of 21.06% is achieved in the ZSO-based device, which is the highest value for RTP-PSCs. The ZSO-based PSCs also exhibit high device stability. Moreover, the efficiency of a large-area perovskite module based on ZSO ETL reaches 17.79%.

Two star-shape triazinane molecules, cyanuric acid (CA) and trisbutylhydroxybenzyl isocyanuric acid (TPCA) having multifunctional groups, are employed as additive and surface modifier in inverted PSCs. Excessive CA and PbI₂ formed highly stable 2D structure at GBs. The devices modified by CA + TPCA combination processes demostrate reduced defect density and enhanced power conversion efficiency and stabilities.

Active layers of p–i–n organic–inorganic hybrid perovskite solar cells (PSCs) are passivated by star-shape, multifunctional triazinane molecules, cyanuric acid (CA), and Tris(dibutylhydroxy- benzyl)isocyanuric acid (TPCA). The most interesting is that CA is used as a bulk additive is able to induce a two-dimensional (2D) structure at grain boundaries (GBs) of the perovskite when excess PbI₂ is present. TPCA is also important to use as a perovskite surface modifier and to reduce the defects in perovskite layer further. The reduced ideality factors, enhanced photoluminescence, and prolonged lifetimes all indicate suppression of non-radiative recombination. The combination of the two substantially improves fill-factors and open-circuit voltages of the devices. This leads to markedly enhanced stabilities of the devices.

An air-stable n dopant named EMIC is introduced to perovskite films, which can effectively n dope perovskite films and prolong electron diffusion length to over 1.21 microns. The doped perovskite solar cells and modules processed by blade-coating realize high power conversion efficiencies of 24.3% and 20.6% at 7.4 mm² and 25.0 cm² aperture areas, respectively.

Abstract

N doping is an essential strategy to prolong electron diffusion length and improve the photovoltaic performance of p–i–n structured perovskite solar devices, but current n-dopants generally suffer from air instability, poor compatibility with perovskites, and the compensation from perovskite intrinsic defects, thus limiting their doping effectiveness. To address these issues, in this work, a new perovskite n-doping strategy is developed by incorporating an air-stable n-dopant (1-ethyl-3-methylimidazolium-2-carboxylate, EMIC) that has no detrimental effects on perovskite crystallinity and morphology. EMIC is soluble in most polar solvents and can be readily introduced into perovskite precursor solutions. Upon thermal annealing of perovskite films, the decarboxylation of EMIC releases imidazolylidene, a reactive species that highly tends to donate electrons and thus efficiently prolongs the electron diffusion length from 0.57 µm to over 1.21 µm. As a result, the blade-coated perovskite solar cells and modules realize high power conversion efficiencies of 24.3% and 20.6% at 7.4 mm² and 25.0 cm² aperture areas, respectively.