Chen Weijie

With the incorporation of fluorinated organic ammonium (4-trifluoromethyl phenethyl ammonium iodide (4FPAI)), high-efficiency 2D/3D perovskite solar cells are fabricated by one step spin coating. The 4FPAI-treated film shows improved crystallization, enhanced charge transport as well as significantly improved moisture stability thereby yielding the resulting device with a champion power conversion efficiency of 22.12% and improved device stability.

Despite the prominent photovoltaic performance and broad application prospect of perovskite solar cells (PVSCs), a significant challenge for their commercialization is the stability issue. Herein, a fluorinated organic ammonium salt, 4-trifluoromethyl phenethyl ammonium iodide (4FPAI), is utilized for the spontaneous formation of gradient 2D/3D perovskite which can be prepared by a simple one-step spin-coating process with low-dimensional phases on the surface and high-dimensional phases at the bottom. The introduction of 4FPAI leads to improved charge transport as well as reduced nonradiative recombination. The optimal 4FPAI-based PVSC exhibits a power conversion efficiency (PCE) of 22.12% which is higher than that of the control PVSC without the 4FPAI treatment (20.87%). Meanwhile, the encapsulated 4FPAI-based device remains at about 88% of its initial PCE under ambient air exposure for 80 days, demonstrating its improved moisture resistance compared to the reference device. This work provides an important strategy for fabricating high efficiency and long-term stable 2D/3D PVSCs.

Herein, a way to control the defects and voids by ternary solvent engineering is demonstrated. The power conversion efficiency with the ternary solvent increases by over 20% with uniform perovskite morphology with minimal defects. Additionally, ternary solvent engineering can be beneficial from an industrial perspective for achieving stable and uniform large-area perovskite devices.

Recent reports reveal that a smooth and uniform surface morphology can endow perovskite solar cells with excellent stability and remarkable power conversion efficiency (PCE). Herein, a ternary solvent strategy is employed using dimethylformamide (DMF), dimethyl-sulfoxide (DMSO), and γ-butyrolactone (GBL) to improve contact between the charge transporting layers and the perovskite layer. This approach yields enhanced surface morphology, charge extraction, and passivation. The thermally stable intermediates generated through the ternary solvent promote uniform MAPbI₃ films with a smooth surface. These intermediates reduce surface roughness, increase grain size, and fill voids or defects in MAPbI₃ due to a strong interaction of ternary solvent. The PCE with the ternary solvent (DMF:GBL:DMSO) increases to 20.23% compared to binary solvents of GBL:DMSO and DMF:DMSO. Additionally, ternary solvent engineering is beneficial from an industrial perspective for achieving a stable and uniform morphology of perovskite in large-area device fabrication.

The study introduces real-time J–V absorbance spectroscopy for observing halide segregation in mixed halide perovskite solar cells under broadband light. This novel setup enables concurrent J–V measurements and absorbance spectra collection, offering in situ analysis of light-induced degradation. The research emphasizes the significance of experimental conditions like humidity and voltage injection, advocating for meticulous characterization of perovskite solar cells under realistic conditions.

Abstract

In this work, a novel real-time current-voltage (J–V) absorbance spectroscopy (RTJAS) setup is introduced for directly observing halide segregation in mixed halide perovskite solar cells under broadband light illumination, simulating solar exposure. The setup incorporates a broadband light source calibrated to one sun irradiation and a CMOS camera for simultaneous capture of all diffracted wavelengths. J–V measurements are performed concurrently with absorbance spectra collection, enabling in situ analysis of light-induced degradation due to halide segregation, including bandgap shifts and cell performance data. Comparison of photoluminescence measurements with RTJAS data reveals differing rates of bandgap decrease, underscoring the advantages of real-time measurement techniques. The work highlights the importance of accounting for experimental conditions, such as humidity and voltage injection, which can accelerate halide segregation, ultimately emphasizing the need for careful consideration of experimental conditions to accurately characterize perovskite solar cell behavior under realistic conditions.

In this work, by introducing ─NH₃ ⁺ rich proline hydrochloride as a versatile medium for buried interface in flexible perovskite solar cells, it not only provides a solid α-phase FAPbI₃ template but also prevents the phase transition induced degradation. A new record power conversion efficiency of 24.61% is achieved. Besides, the devices demonstrate excellent shelf-life/light soaking stability and mechanical stability.

Abstract

The buried interface of the perovskite layer has a profound influence on its film morphology, defect formation, and aging resistance from the outset, therefore, significantly affects the film quality and device performance of derived perovskite solar cells. Especially for FAPbI₃, although it has excellent optoelectronic properties, the spontaneous transition from the black perovskite phase to nonperovskite phase tends to start from the buried interface at the early stage of film formation then further propagate to degrade the whole perovskite. In this work, by introducing ─NH₃ ⁺ rich proline hydrochloride (PF) with a conjugated rigid structure as a versatile medium for buried interface, it not only provides a solid α-phase FAPbI₃ template, but also prevents the phase transition induced degradation. PF also acts as an effective interfacial stress reliever to enhance both efficiency and stability of flexible solar cells. Consequently, a champion efficiency of 24.61% (certified 23.51%) can be achieved, which is the highest efficiency among all reported values for flexible perovskite solar cells. Besides, devices demonstrate excellent shelf-life/light soaking stability (advanced level of ISOS stability protocols) and mechanical stability.

Three novel polymer acceptors based on quinoxaline units are synthesized. Central core substitutions are modified and achieve systemic adjustment of aggregation ability and interaction with polymer donor PM6, leading to different film-formation processes. As a result, PM6:PQx3-based devices deliver high power conversion efficiencies (18.06%, one of the highest values for binary all-polymer solar cells), excellent film-thickness tolerance, and superior stability.

Abstract

Molecular interactions and film-formation processes greatly impact the blend film morphology and device performances of all-polymer solar cells (all-PSCs). Molecular structure, such as the central cores of polymer acceptors, would significantly influence this process. Herein, the central core substitutions of polymer acceptors are adjusted and three quinoxaline (Qx)-fused-core-based materials, PQx1, PQx2, and PQx3 are synthesized. The molecular aggregation ability and intermolecular interaction are systematically regulated, which subsequently influence the film-formation process and determine the resulting blend film morphology. As a result, PQx3, with favorable aggregation ability and moderate interaction with polymer donor PM6, achieves efficient all-PSCs with a high power conversion efficiency (PCE) of 17.60%, which could be further improved to 18.06% after carefully optimizing device annealing and interface layer. This impressive PCE is one of the highest values for binary all-PSCs based on the classical polymer donor PM6. PYF-T-o is also involved in promoting light utilization, and the resulting ternary device shows an impressive PCE of 18.82%. In addition, PM6:PQx3-based devices exhibit high film-thickness tolerance, superior stability, and considerable potential for large-scale devices (16.23% in 1 cm² device). These results highlight the importance of structure optimization of polymer acceptors and film-formation process control for obtaining efficient and stable all-PSCs.

Using scalable room temperature techniques in constructing perovskite solar cells is one of the main challenges toward their simplified processing. Herein, scalable pulsed laser deposition is used as a damage-free, dry, and single-source method to deposit SnO₂ in p–i–n perovskite solar cells showing on par efficiencies with state-of-the-art atomic layer deposited SnO₂.

Pulsed laser deposition (PLD) has already been adopted as a low damage deposition technique of transparent conducting oxides on top of sensitive organic charge transport layers in optoelectronic devices. Herein, SnO₂ deposition is demonstrated as buffer layer in p–i–n perovskite solar cells (PSCs) via wafer-scale (4 inch) PLD at room temperature. The PLD SnO₂ properties, its interface with perovskite/C₆₀, and device performance are compared to atomic layer deposited (ALD) SnO₂, i.e., state-of-the-art buffer layer in perovskite-based single junction and tandem photovoltaics. The PLD SnO₂-based solar cells exhibit on par efficiencies (17.8%) with that of SnO₂ fabricated using ALD. The solvent-free room temperature processing and wafer-scale approach of PLD open up possibilities for buffer layer formation with increased deposition rates while mitigating potential thermal or physical damage to the top organic layers. This is a promising outlook for fully physical vapor-processed halide PSCs and optoelectronic devices requiring low thermal budget.

A patterned insulator contact (PIC) is presented to overcome the passivation-transport trade-off. It is realized by patterning the thermally-evaporated metal fluorides. This PIC has a high coverage of ≈80% and a thickness tolerance increased by 3–5, achieving a power-conversion efficiency of 25% in p–i–n perovskite solar cells.

Abstract

Including an ultrathin insulator interlayer at the perovskite/charge transport interface is a critical strategy for suppressing surface recombination in state-of-the-art perovskite solar cells. However, its further improvement with increased thickness faces a trade-off due to the exponentially inhibited electrical transport. Here, a patterned insulator contact (PIC) design is presented to overcome this passivation-transport trade-off where the conventional ultrathin interlayer is replaced by a thicker counterpart with local openings. Such a PIC is realized using metal fluorides with a high coverage of 80% and a thickness tolerance increased by 3–5. Balancing inhibited transport via local openings is verified by direct observation with local photocurrent mapping. It revealed the atomic passivation mechanism of hydrogen bonding between fluoride ions and perovskite organic cations. It extends the top-surface passivation to double-sided passivation and find that LiF-modified substrate improves the wettability and promotes the out-of-plane growth of perovskite. These combined advances and distilled knowledge allow us to achieve power-conversion-efficiency (PCE) of 25% (certified 24.95%) in p–i–n perovskite solar cells by simultaneously enhancing the open-circuit voltage (V _oc) and the fill factor (FF). The device's reproducibility and operational stability are also improved.

A post-surface engineering strategy called the “clean-passivate” method is proposed to address the problems of perovskite interfaces. A clean and passivated perovskite surface is demonstrated to realize efficient and stable FA_xCs_1-xPbI₃-based devices with inverted structure. Finally, the inverted FA_xCs_1-xPbI₃ perovskite solar cell achieves an efficiency of 24.27%. An initial efficiency of 97.12% after continuous light soaking for 1500 h.

Abstract

Formamidinium-cesium triiodide (FA_xCs_1-xPbI₃) perovskite exhibits excellent phase stability, making it the most promising candidate for commercial perovskite solar cell (PSC) applications, particularly those with inverted structures present a promising contribution to the field of perovskite production. However, this composition often forms small grain sizes and has a large number of defects and PbI₂ residues on its surface, which can damage device performance. In this study, a post-surface engineering strategy called the “clean-passivation” method is proposed to address the interfacial problem between the perovskite and the electron transport layer (ETL). This method significantly reduces surface and grain boundary defects and eliminates unreacted PbI₂, resulting in suppressed iodine decomposition and ion migration during operation. As a result, an excellent power conversion efficiency of 24.27% with superior stability is achieved, as the unencapsulated device maintains 97.12% of its initial efficiency after 1500 h of continuous light soaking. Furthermore, this new surface clean-passivate strategy can be universally applied to other typical perovskite compositions.

3D/2D structured PSCs, realized with phenylethylammonium iodide based salts ( x-XPEAI; x : o, m, p; X: F, Cl, Br), that are synthesized by simple three-step method, have significant impact on photovoltaic device performance and stability. It is shown that salts substituted at meta positions with halogens outperform their -o and -p analogs independent of the halogen type due to favorable surface dipoles supported by detailed density functional theory analyses.

Abstract

Surface passivation with 2D perovskites is a powerful strategy to achieve improved stability and performance in perovskite solar cells (PSCs). Various large organic cations have been successfully implemented, led by phenylethylammonium (PEA⁺ ) and its derivatives. However, systematic studies on large sets of cations to understand the effect of substituent position on 2D perovskite passivation and device performance are lacking. Herein, a collection of halogenated PEA⁺ iodide salts ( x-XPEAI where x : ortho (o), meta (m), para (p), X: F, Cl, Br) are synthesized by a facile method and deposited on top of 3D perovskite. The 2D perovskite layer formation is confirmed by X-ray diffraction (XRD) and grazing-incidence wide-angle X-ray scattering  analyses for all cations, regardless of the nature and position of the halogen. Density functional theory analysis reveals that lower formation energies and higher interfacial dipoles achieved by m-substituted cations are responsible for enhanced performance compared to their o- and p- counterparts. While the m-BrPEAI-treated device shows a champion efficiency of 23.42%, (V _OC=1.13 V, FF=81.2%), considering average efficiencies, stability, and reproducibility, the treatment with m-ClPEAI salt yields the best overall performance. This comprehensive study provides guidelines for understanding the influence of large cation modification on performance and stability of 3D/2D PSCs.

Ternary all-polymer solar cells comprising two polymer donors (D1 and D2) and one polymer acceptor (A) are prepared. The systematic study demonstrates that a pseudo-binary blend morphology with a mixed D1 and D2 domain and an A domain allows broad tunability of the open-circuit voltage and composition tolerance of the fill factor.

Abstract

Tuning the open-circuit voltage (V _OC) and fill factor (FF) without sacrificing the short-circuit current density is crucial for achieving performance advantages in ternary blend organic solar cells as an alternative to the binary ones. This study investigates ternary all-polymer solar cells comprised of two polymer donors (D1 and D2) and one polymer acceptor (A), using two types of D2 polymers with different compatibilities with D1. As demonstrated by photoelectron yield spectroscopy, the ionization energy (IE) of the ternary blends continuously shifts between the IEs of D1:A and D2:A binary blends when D2 forms a single indistinguishable domain with D1. In contrast, the IE of the blends does not exhibit any noticeable change when D2 induces distinct phase separation with D1. Models describing the blend composition dependence of the V _OC and FF are constructed by correlating the effects of the blend morphology and the shift in the energy level of the hole-transporting state in the ternary blends. This study demonstrates that a pseudo-binary blend morphology with a mixed D1 and D2 donor domain and an A acceptor domain is necessary to obtain a broad tunability of V _OC and tolerance of FF to the blend composition in ternary all-polymer solar cells.

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part A

Author(s): Xiaodong Hu, Yongyan Pan, Jianan Wang, Zonghao Liu, Wei Chen

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part B

Author(s): Junyi Xu, Andreas Späth, Wolfgang Gruber, Anastasiia Barabash, Philipp Stadler, Kirill Gubanov, Mingjian Wu, Karen Forberich, Erdmann Spiecker, Rainer H. Fink, Tobias Unruh, Iain McCulloch, Christoph J. Brabec, Thomas Heumüller

Publication date: 11 January 2024

Source: Chem, Volume 10, Issue 1

Author(s): Bo Li, Shuai Li, Jianqiu Gong, Xin Wu, Zhen Li, Danpeng Gao, Dan Zhao, Chunlei Zhang, Yan Wang, Zonglong Zhu

Herein, thermal treatment and the introduction of asymmetric small molecule acceptors are combined to jointly regulate the solubility and crystallinity of the active layer. Based on this strategy, green solvent processed organic solar cells with power conversion efficiency of 17.89% are fabricated, which provides a new idea for the preparation of eco-friendly organic solar cells with high efficiency and high stability.

Using green solvents to fabricate high-efficiency organic solar cells (OSCs) is the ultimate choice for realizing commercial application of OSCs. However, the low solubility of conventional materials in green solvents and unfavorable phase separation limit the development of green solvent-processed organic solar cells (GSP-OSCs). To solve the above problems, a new strategy in which asymmetric acceptor and thermal processing jointly optimize the device performance is proposed. PM6 with temperature-dependent aggregation property is chosen as the donor, and thermal treatment can improve its solubility. The asymmetric small molecule acceptor BTP-2F2Cl is chosen as the third material due to its strong crystallinity and good miscibility with the main system materials. Meanwhile, BTP-2F2Cl can induce the formation of well-ordered crystallization and molecular stacking in the active layer material, which promotes charge transport and inhibits recombination. Therefore, the PM6: L8-BO: BTP-2F2Cl-based ternary GSP-OSCs achieve a champion power conversion efficiency of 17.89% compared with the binary devices (16.99%). The results indicate that the introduction of asymmetric acceptor and thermal treatment are an effective strategy to regulate the active layer morphology and enhance the performance of GSP-OSCs.

The up-conversion (UC) and down-conversion (DC) play a great role in extending the spectral response of the perovskite solar cells (PSCs) and improving both the power conversion efficiency and the stability of the devices. This review provides a comprehensive overview of the recent advances of the rear-earth-based UC/DC techniques in PSCs.

Perovskite solar cells (PSCs) have been considered as one of the most promising photovoltaics, and the power conversion efficiency (PCE) has been boosted to 26.0% in 2023. Extending the spectral absorption range and improving the utilization rate of incident light is one of the effective strategies to further improve the PCE of PSCs. Up-conversion (UC) and down-conversion (DC) can convert low-energy or high-energy photons into visible light, and the luminesced visible light can be further absorbed by the photoactive layer to generate extra photocurrent. Therefore, UC and DC effects offer the potential of broadening the spectral absorption range and the possibility of overcoming the Shockley–Queisser limit for the single-junction solar cell. In this review, the spectral-converting mechanism underling the rare-earth-based UC/DC processes is first discussed. Then recent advances in UC/DC applications in PSCs are comprehensively reviewed. Finally, a concise summary and the challenges for the future development of UC/DC in PSCs are outlined.

Nature Communications, Published online: 30 September 2023; doi:10.1038/s41467-023-41853-y

Publication date: January 2024

Source: Journal of Energy Chemistry, Volume 88

Author(s): Devthade Vidyasagar, Yeonghun Yun, Jae Yu Cho, Hyemin Lee, Kyung Won Kim, Yong Tae Kim, Sung Woong Yang, Jina Jung, Won Chang Choi, Seonu Kim, Rajendra Kumar Gunasekaran, Seok Beom Kang, Kwang Heo, Dong Hoe Kim, Jaeyeong Heo, Sangwook Lee

TEA₂PbI₄ and TEA₂PbBr₄ 2D perovskites are directly employed for surface passivation in hybrid perovskite solar cells with a 3D structure. The passivated perovskite devices demonstrate enhanced surface morphology when compared to the devices utilizing 3D perovskites. Furthermore, the solar cells with surface passivation exhibit significantly higher efficiency in comparison to conventional 3D perovskite solar cells.

Surface passivation of 3D perovskites with highly stable 2D perovskite is an effective strategy to improve both performance and stability of perovskite solar cells (PSCs). Herein, a new approach has been employed for the synthesis of oleic acid and octylamine-assisted 2D perovskites TEA₂PbX₄ (X = I, Br) in antisolvent and directly used them for the surface passivation of MAFAPbI₃ (3D) perovskite. The grain boundary and interface are both optimized in 3D/2D perovskite by 2D perovskite to improve surface morphology. It is found that the 2D perovskite effectively suppresses carrier recombination by reducing the defect density and facilitates interfacial charge extraction through better energy-level alignments. As a result, power conversion efficiency of PSCs is boosted up to 18.56% and 19.87% for passivation with TEA₂PbI₄ and TEA₂PbBr₄, respectively. The passivated perovskite devices exhibit good thermal, operational, and long-term stability in an ambient environment because of the material robustness of 3D/2D hybrid perovskites.

Perovskite solar cells (PSCs) encounter phase segregation, component loss, lattice distortion, and fatigue failure, impacting their operational stability. Developing self-healing perovskites to enhance stability under harsh stimuli is a prominent research focus. This review categorizes and summarizes PSCs' self-healing behavior, exploring recent advances, mechanisms, strategies, and challenges, and providing valuable insights for future studies.

Abstract

Perovskite solar cells have achieved rapid progress in the new-generation photovoltaic field, but the commercialization lags behind owing to the device stability issue under operational conditions. Ultimately, the instability issue is attributed to the soft lattice of ionic perovskite crystal. In brief, metal halide perovskite materials are susceptible to structural instability processes, including phase segregation, component loss, lattice distortion, and fatigue failure under harsh external stimuli such as high humidity, strong irradiation, wide thermal cycles, and large stress. Developing self-healing perovskites to further improve the unsatisfactory operational stability of their photoelectric devices under harsh stimuli has become a cutting-edge hotspot in this field. This self-healing behavior needs to be studied more comprehensively. Therefore, the self-healing behavior of the metal halide perovskites and photovoltaics is classified and summarized in this review. By discussing recent advances, underlying mechanisms, strategies, and existing challenges, this review provides perspectives on self-healing of perovskite solar cells in the future.

In this work, the issue of efficiency loss due to increased cell size for indoor perovskite photovoltaics by developing an in situ pre-nucleation strategy is addressed. A trace amount of β-alaninamide hydrochloride (AHC) is introduced into the perovskite precursor solution, which spontaneously reacts with PbI₂ to form 2D perovskite seed crystals to facilitate 3D perovskite growth.

Abstract

With 40% efficiency under room light intensity, perovskite solar cells (PSCs) will be promising power supplies for low-light applications, particularly for Internet of Things (IoT) devices and indoor electronics, shall they become commercialized. Herein, β-alaninamide hydrochloride (AHC) is utilized to spontaneously form a layer of 2D perovskite nucleation seeds for improved film uniformity, crystallization quality, and solar cell performance. It is found that the AHC addition indeed improves film quality as demonstrated by better uniformity, lower trap density, smaller lattice stress, and, as a result, a 10-fold increase in charge carrier lifetime. Consequently, not only does the small-area (0.09 cm²) PSCs achieve a power conversion efficiency of 42.12%, the large-area cells (1.00 cm², and 2.56 cm²) attain efficiency as high as 40.93%, and 40.07% respectively. All of these are the highest efficiency values for indoor photovoltaic cells with similar sizes, and more importantly, they represent the smallest efficiency loss due to area scale-up. This work provides a new method to fabricate high-performance indoor PSCs (i-PSCs) for IoT devices with great potential in large-area printing technology.

Nature, Published online: 28 September 2023; doi:10.1038/s41586-023-06667-4

In this study, two novel small molecular of ZH1 and ZH2 are developed for organic solar cells (OSCs). It is observed that precise manipulation of end groups of acceptors can simultaneously optimize the morphology and improve the efficiency, stability, promoting the development of the high-performance OSCs.

Abstract

Introducing the guest materials into binary active layer to construct ternary organic solar cells (OSCs) is widely used to improve device performance. Nevertheless, designing the guest materials is a challenging task. Herein, asymmetric alloy acceptor strategy guided by similarity principle to design the guest materials is employed. Two small molecular acceptors (ZH1 with symmetric end groups and ZH2 with asymmetric end groups) with the same skeleton to the host acceptor are synthesized and compared. Compared to symmetric ZH1, asymmetric ZH2 delivers a remarkably higher efficiency (3.86% vs 13.03%) when paired with PM6, benefiting from the larger dipole moment to facilitate charge dynamics and more favorable morphology. More importantly, by introducing ZH1 and ZH2 as the guest materials into the PM6:BTP-eC9 blend, both ZH1 and ZH2 well alloy with acceptor BTP-eC9 due to the similar skeleton, not only providing a complementary absorption, but also optimizing and stabilizing the blend morphology. Notably, the asymmetric alloy acceptor distinctly outperforms symmetric alloy acceptor, PM6:BTP-eC9:ZH2-based device achieves an outstanding efficiency of 18.75% with better stability and reduced non-radiative energy loss. Therefore, developing asymmetric alloy acceptor is an effective strategy to develop high-performance and stable OSCs.

Self-triggered spin-polarized coherent light emission is achieved through stimulated emission of imbalanced spin population in the 3D@1D perovskites. The population is produced by exciton chirality transfer from chiral 1D perovskites to achiral 3D perovskites without external spin injection. The compositions of 3D@1D perovskites are tailored for broadband output of spin-polarized amplified spontaneous emission with distinct degree of polarization.

Abstract

Spin-polarized lasers, arising from stimulated emission of imbalanced spin populations, play a vital role in spin-optoelectronics. It is usually tackled by external spin injection, inevitably suffering from additional losses across the barriers from injection sources to gain materials. Herein, spin-polarized coherent light emission is self-triggered from the 1D-anchoring-3D perovskites, where the imbalanced populations in achiral 3D perovskites are endowed with the spin selectivity of exciton chirality (EC) underpinned by chiral 1D perovskites. Efficient transfer of EC is enabled by rapid energy transfer, thereby creating an imbalance of the spin population of excited states. Stimulated emission of such populations brings self-triggered spin-polarized amplified spontaneous emission in the composite perovskites, yielding a higher degree of polarization (DOP) than that based on optical spin injection into bare achiral 3D perovskites. Chemical diversity of composite perovskites not only enables to adjust band gap for broadband output of spin-polarized light signals but also promises to manipulate radiative decay and spin relaxation toward remarkably increased DOP. These results highlight the importance of EC transfer mechanism for spin-polarized lasing and represent a crucial step toward the development of chiral-spintronics.

Highly conductive and transparent indium tin oxide is introduced by sputtering as recombination electrode for tandem solar cells (TSCs), and dual-functional C1 is employed as both transport and protective layer to avoid damaging the underlying material during sputtering and enhance electron transport. Monolithic perovskite/organic TSC with high power conversion efficiency of 24.07% and excellent stability is demonstrated.

Abstract

Rational selection and design of recombination electrodes (RCEs) are crucial to enhancing the power conversion efficiency (PCE) and stability of monolithic tandem solar cells (TSCs). Sputtered indium tin oxide (ITO) with high conductivity and excellent transmittance is introduced as RCE in perovskite/organic TSCs. To prevent high-energy ITO particles destroy the underlying material during sputtering, dual-functional transport and protective layer (C1) is employed. The styryl group in C1 can be thermally crosslinked to serve as a sputtering protective layer. Meanwhile, the conjugated phenanthroline skeleton in C1 shows high electron mobility and hole blocking capability to promote the electron transport process at the interfaces and effectively reduce charge accumulation. Monolithic perovskite/organic TSC with high PCE of 24.07% and excellent stability is demonstrated by stacking a 1.77 eV bandgap perovskite layer and a 1.35 eV bandgap organic active layer. This strategy provides new insights for overcoming the fundamental efficiency limits of single-junction devices and promotes the further development of TSC devices.

The morphologies of non-fused electron acceptor ASe-5 are studied by selecting two high-efficiency polymer donors, PBDB-TF and PBQx-TF, and the PBQx-TF-based device achieves higher power conversion efficiency of 14.7% due to better phase separation.

Abstract

Non-fused electron acceptors have huge advantages in fabricating low-cost organic photovoltaic (OPV) cells. However, morphology control is a challenge as non-fused C─C single bonds bring more molecular conformations. Here, by selecting two typical polymer donors, PBDB-TF and PBQx-TF, the blend morphologies and its impacts on the power conversion efficiencies (PCEs) of non-fused acceptor-based OPV cells are studied. A selenium-containing non-fused acceptor named ASe-5 is designed. The results suggest that PBQx-TF has a lower miscibility with ASe-5 when compared with PBDB-TF. Additionally, the polymer networks may form earlier in the PBQx-TF:ASe-5 blend film due to stronger preaggregation performance, leading to a more obvious phase separation. The PBQx-TF:ASe-5 blend film shows faster charge transfer and suppressed charge recombination. As a result, the PBQx-TF:ASe-5-based device records a good PCE of 14.7% with a higher fill factor (FF) of 0.744, while the PBDB-TF:ASe-5-based device only obtains a moderate PCE of 12.3% with a relatively low FF of 0.662. The work demonstrates that the selection of donors plays a crucial role in controlling the blend morphology and thus improving the PCEs of non-fused acceptor-based OPV cells.

This study elucidates the formation dynamics and film structure of 2D-Dion-Jacobson phase on a template of 3D triple-cation perovskite films via in situ X-ray scattering. The solvent-induced surface reconstruction of the template allows the control of phase and phase distribution in 2D films. The tailored energy landscape of 2D/3D heterostructures leads to highly efficient and stable inverted perovskite solar cells.

Abstract

2D-on-3D (2D/3D) perovskite heterostructures present a promising strategy to realize efficient and stable photovoltaics. However, their applicability in inverted solar cells is limited due to the quantum confinement of the 2D-layer and solvent incompatibilities that disrupt the underlying 3D layer, hampering electron transport at the 2D/3D interface. Herein, solvent-dependent formation dynamics and structural evolution of 2D/3D heterostructures are investigated via in situ X-ray scattering. It is revealed that solvent interaction with the 3D surface determines the formation sequence and spatial distribution of quasi-2D phases with n = 2–4. Isopropanol (IPA) reconstructs the perovskite into a PbI₂-rich surface, forming a strata with smaller n first, followed by a thinner substratum of larger n. In contrast, 2,2,2-Trifluoroethanol (TFE) preserves the 3D surface, promoting the formation of uniformly distributed larger n domains first, and smaller n last. Leveraging these insights, Dion–Jacobson perovskites are used with superior charge transport properties and structural robustness to fabricate 2D/3D heterostructures dominated by n ≥ 3 and engineer a favorable energy landscape for electron tunneling. Inverted solar cells based on 3-Aminomethylpyridine and TFE achieve a champion efficiency of 23.60%, with V _oc and FF of 1.19 V and 84.5%, respectively, and superior stabilities with t ₉₄ of 960 h under thermal stress.