Chen Weijie

Low-cost hole transport materials T3, featuring a substituted pyrrole core and triphenylamine peripheral arms, have been designed and synthesized for high performance perovskite solar cells. The capability of functionalization in the final synthetic step provides an efficient way to tune energy levels and other properties of T3 materials.

Abstract

Hole transport materials (HTMs) with high hole mobility, good band alignment and ease of fabrication are highly desirable for perovskite solar cells (PSCs). Here, we designed and synthesized novel organic HTMs, named T3, which can be synthesized in high yields with commercially available materials, featuring a substituted pyrrole core and triphenylamine peripheral arms. The capability of functionalization in the final synthetic step provides an efficient way to obtain a variety of T3-based HTMs with tunable energy levels and other properties. Among them, fluorine-substituted T3 (T3-F) exhibits the best band alignment and hole extraction properties, leading to PSCs with outstanding PCEs of 24.85 % and 24.03 % (certified 23.46 %) for aperture areas of 0.1 and 1 cm², respectively. The simple structure and tunable performance of T3 can inspire further optimization for efficient PSCs.

Surface passivation can reduce defects in the perovskite film. It is shown that exposing a preannealed perovskite film to a mild ethylenediamine vapor environment lowers the defect density by four times, enhances radiative yield and improves the device performance. The impact of these defects on the operational stability is investigated by tracking the hysteresis index.

Defects present at the surface or within the bulk of halide perovskites act as a barrier to charge transfer/transport, induce nonradiative recombination thereby limit open-circuit voltage (V _OC), and accelerate degradation in the perovskite solar cells (PSCs). Passivation of these defects at surfaces, interfaces, and grain boundaries to suppress the charge recombination is therefore imperative to improving photovoltaic performance in the PSCs. Herein, a facile posttreatment of perovskite surface by ethylenediamine (EDA) via mixed solvent vapor annealing method is reported. The results show that only a trace amount of EDA causes significant suppression of nonradiative recombination leading to over 100 mV increased V _OC and ≈22% improvement in power conversion efficiency (PCE) of the inverted PSCs. The key reasons for this improvement are an upward shift in the Fermi energy level, reduced lattice strain and Urbach energy, and reduction in nonradiative recombination upon EDA passivation. These lead to a PCE exceeding 20% up from 16% for a nonpassivated film. The unencapsulated EDA-modified PSCs also demonstrate an improved shelf-life and retain 87% of the initial PCE after 850 h.

The 5 key technologies (Data sources and regularization; Feature extraction and transformation of molecular descriptors; Selection of suitability algorithms; Model validation and optimization; Model interpretation), applications, milestone research, urgent challenges and future application directions of machine learning in the field of perovskite solar cells, and component materials are reviewed.

Abstract

Data-driven epoch, the development of machine learning (ML) in materials and device design is an irreversible trend. Its ability and efficiency to handle nonlinear and game-playing problems is unmatched by traditional simulation computing software and trial-error experiments. Perovskite solar cells are complex physicochemical devices (systems) that consist of perovskite materials, transport layer materials, and electrodes. Predicting the physicochemical properties and screening the component materials related to perovskite solar cells is the strong point of ML. However, the applications of ML in perovskite solar cells and component materials has only begun to boom in the last two years, so it is necessary to provide a review of the involved ML technologies, the application status, the facing urgent challenges and the development blueprint.

Polar molecules with different degrees of dipole moments are proposed to terminate the perovskite structure by forming the dipole interlayer. The introduction of a dipole interlayer not only adjusts the energy level alignment, but also the functional groups present can coordinate with the Pb atoms at the surface of the perovskite film to reduce the defect content and facilitate the carrier extraction.

Abstract

The ionic nature of the organic-inorganic hybrid perovskite material is prone to react with different functional groups. Here, a series of polar molecules with permanent dipole moments are designed to modify the perovskite surface termination. It is observed that proper interfacial design can significantly reduce trap state density for effective charge transfer. The energy level of the substrate can be adjusted by the magnitude and direction of the dipole moment. As a result, a high 24.54% photo-electric conversion efficiency is reached by introducing pentafluoride benzene moieties with carboxylic functional groups. In addition, the humidity and heat stability of the perovskite device is obviously improved. This work demonstrates the importance of chemical interactions at perovskite termination and paves the way for further enhancing the performance of perovskite solar cells.

The ionic liquid, methylammonium formate (MAFm), based dual-interface engineering is developed to modify the bottom and top interfaces of wide-bandgap CsPbI₂Br films, which enables a high PCE of 17.0% and V _OC of 1.347 V for CsPbI₂Br-based wide-bandgap sub-cells. High-efficiency monolithic perovskite/organic tandem solar cells based on these sub-cells demonstrate a champion PCE of 23.21% and V _OC of 2.10 V.

Abstract

Monolithic perovskite/organic tandem solar cells (POTSCs) have significant advantages in next-generation flexible photovoltaics, owing to their capability to overcome the Shockley–Queisser limit and facile device integration. However, the compromised sub-cells performance challenges the fabrication of high-efficiency POTSCs. Especially for all-inorganic wide-bandgap perovskite front sub-cells (AIWPSCs) based n-i-p structured POTSCs (AIPOTSCs), for which the power conversion efficiency (PCE) is much lower than organic–inorganic mixed-halide wide-bandgap perovskite based POTSCs. Herein, an ionic liquid, methylammonium formate (MAFm), based dual-interface engineering approach is developed to modify the bottom and top interfaces of wide-bandgap CsPbI₂Br films. In particular, the Fm⁻ group of MAFm can effectively passivate the interface defects, and the top interface modification can facilitate the formation of uniform perovskite films with enlarged grain size, thereby mitigating the defects and perovskite grain boundaries induced carrier recombination. As a result, CsPbI₂Br-based AIWPSCs with a high PCE of 17.0% and open-circuit voltage (V _OC) of 1.347 V are achieved. By integrating these dual-interface engineered CsPbI₂Br-based front sub-cells with the narrow-bandgap PM6:CH1007-based rear sub-cells, a record PCE of 23.21% is obtained for AIPOTSCs, illustrating the potential of AIPOTSCs for achieving high-efficiency tandem solar cells.

Nature Communications, Published online: 15 February 2023; doi:10.1038/s41467-023-36229-1

Publication date: May 2023

Source: Nano Energy, Volume 109

Author(s): Shaobing Xiong, Sheng Jiang, Yefan Zhang, Zhiwei Lv, Ruirong Bai, Yuting Yan, Qi Zeng, Xionghu Xu, Liming Ding, Yuning Wu, Xianjie Liu, Mats Fahlman, Qinye Bao

Bidentate ligand 2,2′-Bipyridine enables a stable chelate structure with uncoordinated Pb(II) on CsPbI_2.6Br_0.4 perovskite surface, thus passivating surface defects. Compared with monodentate ligand pyridine, it has a more stable passivation effect and outstanding anti-dissociation performance. The champion cell achieves an efficiency of 16.57%, which represents a new record efficiency for hole transport material-free inorganic C-PSCs.

Abstract

Molecular passivation on perovskite surface is an effective strategy to inhibit surface defect-assisted recombination and reduce nonradiative recombination loss in perovskite solar cells (PSCs). However, the majority of passivating molecules bind to perovskite surface through weak interactions, resulting in weak passivation effects and susceptible to interference from various factors. Especially in carbon-based perovskite solar cells (C-PSCs), the molecular passivation effect is more susceptible to disturbance in subsequent harsh preparation of carbon electrodes via blade-coating route. Herein, bidentate ligand 2,2′-Bipyridine (2Bipy) is explored to passivate surface defects of CsPbI_2.6Br_0.4 perovskite films. The results indicate that compared with monodentate pyridine (Py), bidentate 2Bipy shows a stronger chelation with uncoordinated Pb(II) defects and exhibits a greater passivation effect on perovskite surface. As a result, 2Bipy-modified perovskite films display a significantly boosted photoluminescence lifetime, accompanied by excellent anchoring stability and anti-dissociation of passivating molecules. Meanwhile, the moisture resistance of the 2Bipy-modified perovskite films is also significantly enhanced. Consequently, the efficiency of C-PSCs is improved to 16.57% (J _sc = 17.16 mA cm⁻², V _oc = 1.198 V, FF = 80.63%). As far as it is known, this value represents a new record efficiency for hole transport material-free inorganic C-PSCs.

Organic solar cells feature a hierarchical structure with the electron donor/acceptor layer sandwiched by the anode and cathode. By calculating the mixing energy, a liquid additive is identified here to selectively solvate the acceptor and solidify the donor during film-formation process. The solvated acceptor diffuses to the top following the liquid vaporization and leaves the donor at bottom, leading to improved performance.

Abstract

Organic solar cells (OSC) feature a hierarchical structure with the electron donor/acceptor layer sandwiched by anode and cathode, which raises the importance of controlling the molecular crystal orientation, domain size, and vertical distribution to facilitate the charge collection at electrodes. However, the similar conjugated backbone of donor/acceptor material and fast film-formation kinetics have led to spinodal-decomposition-orientated phase separation that result in the film presenting an intimately mixed morphology and random molecular orientation. To solve the issue, the mixing Gibbs free energy-triggered solid–liquid phase separation during the film formation process is enhanced by solidifying one component and solvating the other based on a liquid additive. Following the liquid evaporation process, a favorable vertical distribution is obtained. Meanwhile, the prolonged solvation process enlarges the domain size and assists the molecules to diffuse and orient properly, enabling better exciton/charge dynamics during the power conversion processes. As a result, the fabricated devices exhibit a fill factor over 80% and an efficiency of 18.72%, which is one of the top efficiencies for binary OSCs. Insights and a methodology is provided here to manipulate the organic donor/acceptor phase separation in terms of mixing Gibbs free energy.

Sensitive external quantum efficiency measurements combined with energy resolved-electrochemical impedance spectroscopy reveal that ozone, and not water or oxygen, in ambient air is the origin of sub-bandgap defects that occur in polymer donor–non-fullerene acceptor organic solar cells. The defects are primarily located at the top side of the film and arise due to degradation of the polymer donor.

Abstract

Targeted strategies to overcome defects in organic semiconductors require insight into their identity and origin. Here the formation, nature, and location of defects is studied in PM6:Y6 organic solar cells by sensitive EQE measurements. Exposure of the active layer to ambient atmosphere and H₂O-saturated compressed air indicates that a trace constituent in ambient air causes the formation of defects. By exposing the active layer to O₃-enriched air, O₃ is identified as the species creating defects in PM6:Y6 blends. Aging of complete inverted (n–i–p) configuration solar cells in H₂O-saturated compressed air also increases the defect response. This is attributed to a reduced band bending at the PM6:Y6 | MoO₃ hole-collecting contact, caused by a change in work function of MoO₃ interacting with the H₂O, which allows more defect states to be filled and available for photoexcitation. By measuring energy resolved-electrochemical impedance spectroscopy and by fabricating semitransparent cells, regular architecture cells, and semitransparent cells with an optical spacer−mirror stack it is found that defects originate predominantly from PM6 and are located near the top electrode, independent of device polarity. Because O₃ is omnipresent in ambient atmosphere, albeit in small amounts, it likely causes defects in many organic semiconductors exposed to ambient air.

To avoid the iodine loss in perovskite film, this work provides a novel strategy to govern the PbI₆ framework based on a “polymer like” molecule, benzamide. The modified perovskite solar cells (PSCs) show well-tuned level structure and low defect density. And both the performance and long-term stability of PSCs are significantly improved.

Abstract

The unavoidable iodine loss in the perovskite layer is closely related to carrier non-radiative and device degradation. During the post-annealing process, the fragile PbI bond is easy to break, leading to the formation of iodine vacancies and inducing stress-driven structure collapse. Herein, a PbI₆ octahedra stabilization strategy via building robust grain boundary modification networks is developed. The introduction of conjugated structure into amides can significantly enhance their anchoring ability with PbI units, while the π–π stacking effect of benzamide enables a passivation network with polymer-like effect. This is well evidenced by the excellent properties in eliminated iodine loss and stabilized perovskite lattice. Therefore, benzamide modification not only transform the perovskite films from n-type to p-type by suppressing the iodine vacancy-doping effect, but also reduces defect density, ultimately bringing the perovskite layer longer carrier diffusion length and better charge injection efficiency. Finally, the benzamide modified devices realize both high power conversion efficiency of 24.78% and excellent operating stability. Of particular note, the module efficiency with 14 cm² active area is over 21%.

Rational introduction of flexible alkyl chains into coplanar donor–π linker–donor (D–π–D) hole-transporting materials (HTMs) enables synchronous optimization of their solution processability, molecular packing, and thermal phase transition. Favorable self-assembly and surface characteristics of HTMs can facilitate efficient interfacial charge transport/extraction and inhibit detrimental charge recombination in inverted perovskite solar cells, accounting for an enhanced open-circuit voltage and fill factor.

Rational introduction of flexible alkyl chains into rigid conjugated molecules is a facile but effective strategy to develop advanced organic semiconductor materials for considerable enhancement of photovoltaic performance. Herein, seven hole-transporting materials (HTMs) via attaching ethyl, hexyl, or ethylhexyl to benzodithiophene π-linker and bromoethyl, bromobutyl, or bromohexyl to phenoxazine donor (D), respectively, named B₂P₂, B₆P₂, B₈P₂, B₆P₄, B₂P₆, B₆P₆ (N01), and B₈P₆, are reported. Joint differential scanning calorimetry measurements and thin-film absorption spectra of representative HTMs, B₈P₆, B₆P₄, and B₂P₂ reveal that alkyl chain modulation on coplanar D–π–D HTMs enables synchronous optimization of their solution processability, molecular packing, and thermal phase transition. Consequently, benefiting from the favorable self-assembly and surface characteristics of hole-transporting layers and further induced superior upper perovskite-growth, B₈P₆- and B₆P₄ -based inverted perovskite solar cells exhibit decent power conversion efficiencies of 20.67% and 20.13%, respectively, prior to that of amorphous B₂P₂ (19.04%). Analysis on steady-state/transient photoluminescence spectra and light intensity-dependent short-circuit photocurrent and open-circuit voltage (V _oc) demonstrates that more ordered assemblies of HTMs obtained via alkyl chain engineering can facilitate efficient interfacial charge transport/extraction and inhibit detrimental charge recombination, accounting for an enhanced V _oc and fill factor.

A comprehensive review on the state-of-the-art processing methods of low-temperature SnO₂ electron transport layer in perovskite solar cells is provided, highlighting the utilization of various passivation strategies such as additive engineering, surface treatment, and graded multilayers together with large area deposition techniques to enable fabrication of highly stable, efficient, and scalable perovskite photovoltaics.

Perovskite solar cell (PSC) technology experiences a remarkably rapid growth toward commercialization with certified efficiency of over 25%, along with the outstanding breakthrough in the development of SnO₂. Owing to the wide bandgap, high electron mobility, chemical stability, and low photocatalytic activity, SnO₂ has been the rising star to serve as electron transporting layer (ETL). More importantly, the low-temperature fabrication process (<200 °C) enables SnO₂ a promising candidate for the industry, making it compatible with the plastic substrates and large-scale production, which is crucial for the flexible and scalable devices fabrication. In this review, the processing methods (solution-based, vacuum-based, and vapor-based deposition) of low-temperature SnO₂ (LT-SnO₂) and the pros and cons of them with a focus on their scalability are discussed. Additionally, the morphologies of obtained LT-SnO₂ are investigated to guide the design and performance improvement of devices. The modification strategies to reduce undesired nonradiative recombination and passivate the defects in the bulk or at the interface of LT-SnO₂, influencing the quality of perovskite films, together with the efficiency and stability of cells are summarized. This review is a comprehensive overview of the studies on low-temperature SnO₂ ETL and provides detailed instructions for scalable PSCs.

Two-birds-with-one-stone strategies in which defect passivation and connection strengthen the perovskite/spiro-OMeTAD interface are achieved using difluorine modifier 3,5-DFBS for surface treatment. Perovskite solar cells (PSCs) based on the PVK/3,5-DFBS film offer an efficiency of 23.69% with better long-term stability. This work opens up a new avenue to fabricate highly efficient and stable PSCs.

The interface between the perovskite layer and charge transport layer (CTL) plays an important role in the photoelectric conversion of perovskite solar cells (PSCs). In essence, the presence of defects and unideal contact at the perovskite/CTL interface induces severe nonradiative charge recombination, thus limiting the open-circuit voltage and fill factor of PSCs. Herein, a two-birds-with-one-stone strategy to overcome the earlier challenges is reported, in which a single reagent 3,5-difluorobenzenesulfonamide (3,5-DFBS) is applied as an interface modifier between perovskite layer and spiro-OMeTAD hole transport layer (HTL) in conventional PSCs. The 3,5-DFBS molecules can passivate the undercoordinated Pb²⁺-related surface defects by forming coordination through SO group and simultaneously strengthen the perovskite/HTL interface contact via F–π interactions, thus promoting hole extraction greatly. As a result, a champion efficiency of 23.69% with substantially improved stability is accomplished for 3,5-DFBS PSCs. This work demonstrates that the two-birds-with-one-stone strategy is promising for achieving highly efficient and stable PSCs.

Dual-functional PCPDTBT assisted with thermal spin-coating technology is employed as a hole transport layer in CsPbI₂Br-based perovskite solar cells, which effectively solves the instability sources of transport layer and residual strain-induced instability of perovskite layer. Finally, owing to effective charge transport and strain regulation, the optimized device achieves a high efficiency of 16.5% and excellent stability.

Abstract

Numerous strategies have been practiced to improve the power conversion efficiency of CsPbI₂Br-based perovskite solar cells (PSCs), which definitely makes efficiency gradually approach the theoretical efficiency limit. However, sufficient device stability is still in urgent demand for commercialization, pushing to overcome some instability sources induced by hygroscopicity of spiro-OMeTAD and residual strain of perovskite layer. To address these issues, p-type semiconductor of PCPDTBT is used to replace spiro-OMeTAD, enabling dual functions of hole transport and strain regulation. On the one hand, undoped PCPDTBT performs excellent hole extraction and transport, while avoiding the perovskite degradation caused by the hygroscopicity of common additives. On the other hand, PCPDTBT assisted by a thermally spin-coating method compensates for the thermally-induced residual strain in perovskite layer owing to its high thermal expansion coefficient. Consequently, CsPbI₂Br-based PSCs with PCPDTBT layer achieve improved efficiency of 16.5% as well as enhanced stability. This study provides a simple and facile strategy to achieve efficient and stable CsPbI₂Br-based PSCs.

In a high-efficiency ternary matrix platform for all-polymer solar cells, the operational stability enhancement strategy is proposed with carefully studied underlying reasons, in terms of morphology and photo-physics. Based on the “canceling-out” phenomenon, further ternary OPV blend design can be nourished by considering this principle during material combination, which can be useful in boosting both PCE and stability.

Abstract

All-polymer solar cells (All-PSCs) are considered the most promising candidate in achieving both efficient and stable organic photovoltaic devices, yet the field has rarely presented an in-depth understanding of corresponding device stability while efficiency is continuously boosted via the innovation of polymer acceptors. Herein, a ternary matrix is built for all-PSCs with optimized morphology, improved film ductility and importantly, boosted efficiency and better operational stability than its parental binary counterparts, as a platform to study the underlying mechanism. The target system PQM-Cl:PTQ10:PY-IT (0.8:0.2:1.2) exhibits an alleviated burn-in loss of morphology and efficiency under light soaking, which supports its promoted device lifetime. The comprehensive characterizations of fresh and light-soaked active layers lead to a clear illustration of opposite morphological and physical degradation direction of PQM-Cl and PTQ10, thus resulting in a delicate balance at the optimal ternary system. Specifically, the enlarging tendency of PQM-Cl and shrinking preference of PTQ10 in terms of phase separation leads to a stable morphology in their mixing phase; the hole transfer kinetics of PQM-Cl:PY-IT host is stabilized by incorporating PTQ10. This work succeeds in reaching a deep insight into all-PSC's stability promotion by a rational ternary design, which booms the prospect of gaining high-performance all-PSCs.

The optoelectrical properties of nanocrystalline silicon carbide can be tuned over a wide range, depending on the deposition conditions, and a guide for these is given. As a low-conductive layer is needed for the passivation and a high-conductive layer for contacting, the interplay of both layer thicknesses is investigated, and a strong trade-off in passivation and fill factor is found.

Due to its high transparency, silicon carbide can replace amorphous silicon as a front contact material in crystalline silicon solar cells. Herein, first a look at doping in nc-SiC:H with different deposition techniques is taken. Then, the influence of various deposition conditions for hot wire chemical vapor deposition-prepared nc-SiC:H is investigated. Both the electrical conductivity and the optical bandgap increase simultaneously for a multitude of deposition parameters. Combining a high filament temperature of the catalytic filament, a high hydrogen dilution of the precursor gas and an overall low total gas flow, conductivities of 0.38 S cm⁻¹ in combination with an optical bandgap of 3.2 eV can be achieved. In the last section, a closer look into the dependencies of the layer thicknesses of the two different nc-SiC:H layers applied in solar cells on the cell performance is taken. While the layer with conducting properties only has minor influences on cell properties, a trade-off between passivation and fill factor is identified for the passivating nc-SiC:H layer. For thicker layers, the passivating nc-SiC:H layer achieves a very high implied open-circuit voltage above 740 mV, but the fill factor starts to degrade due to a very low conductance of the layer.

I–V measurements of perovskite and organic solar cells during spaceflight are related to solar irradiance, yielding power-conversion efficiencies of up to 13%. Subsequent morphology analysis with X-Ray scattering shows minor morphological changes but promising structural stability of the solar cells that went to space.

Perovskite and organic solar cells are promising for space applications for enabling higher specific powers or alternative deployment systems. However, terrestrial tests can only mimic space conditions to a certain extent. Herein, a detailed analysis of irradiation-dependent photovoltaic parameters of perovskite and organic solar cells exposed to space conditions during a suborbital flight is presented. In orbital altitudes, perovskite and organic solar cells reach power-conversion efficiencies of more than 13% and 6%, respectively. Based on postflight grazing-incidence small-angle and wide-angle X-ray scattering, the active layer morphology and crystalline structure of the returned space solar cells are studied and compared to those of reference solar cells that stayed in an inert atmosphere. Minor changes in the active layer morphology are induced by the sole transport, without causing significant performance loss. For the space solar cells, morphological changes are attributed to the flight experiment that includes rocket launch, spaceflight, and reentry, as well as short-terrestrial environment exposure before and after launch. In contrast, no significant changes to the crystalline phase are observed. The notable performance during flight and high active layer stability, especially of perovskite solar cells, are promising results for further steps toward an orbital demonstration.

A facile and controllable strategy is reported to manipulate the crystallographic orientation of polycrystalline perovskites by employing a cross-linkable organic ligand. The resultant photovoltaic devices can achieve high power conversion efficiency and superior long-term stability. Moreover, cross-linked LDPs within 3D perovskites enable flexible devices with significantly enhanced bending durability.

Abstract

The crystallographic orientation of polycrystalline perovskites is found to be strongly correlated with their intrinsic properties; therefore, it can be used to effectively enhance the performance of perovskite-based devices. Here, a facile way of manipulating the facet orientation of polycrystalline perovskite films in a controllable manner is reported. By incorporating a cross-linkable organic ligand into the perovskite precursor solution, the crystal orientation disorder can be reduced in the resultant perovskite films to exhibit the prominent (001) orientation with a preferred stacking mode. Moreover, the as-formed low-dimensional perovskites (LDPs) between the organic ligand and the excess lead iodide can passivate the defects around the grain boundaries. Consequently, highly efficient p-i-n structured perovskite solar cells (PSCs) can be made in both rigid and flexible forms from modified perovskites to show high power conversion efficiencies (PCE) of 24.12% and 23.23%, respectively. The devices also exhibit superior long-term stability in a humid environment (with T ₉₀ > 1000 h) and under thermal stress (retaining 87% of its initial PCE after 1000 h). More importantly, the ligand enables the derived LDPs to be crosslinked (under 254 nm UV illumination) to demonstrate excellent mechanical bending durability in flexible devices.

The cost of manufacturing solar cells is determined by their roll-to-roll coating speed. Lengthy annealing steps severely limit the effective coating speed of perovskite solar cells (PSCs). Here, a high vapor-pressure precursor ink is solvent-engineered to entirely circumvent such annealing treatments. Fully annealing-free p-i-n PSCs—entirely compatible with roll-to-roll processing—demonstrate power conversion efficiencies (PCEs) over 17%.

Abstract

High temperature post-deposition annealing of hybrid lead halide perovskite thin films—typically lasting at least 10 min—dramatically limits the maximum roll-to-roll coating speed, which determines solar module manufacturing costs. While several approaches for “annealing-free” perovskite solar cells (PSCs) have been demonstrated, many are of limited feasibility for scalable fabrication. Here, this work has solvent-engineered a high vapor pressure solvent mixture of 2-methoxy ethanol and tetrahydrofuran to deposit highly crystalline perovskite thin-films at room temperature using gas-quenching to remove the volatile solvents. Using this approach, this work demonstrates p-i-n devices with an annealing-free MAPbI₃ perovskite layer achieving stabilized power conversion efficiencies (PCEs) of up to 18.0%, compared to 18.4% for devices containing an annealed perovskite layer. This work then explores the deposition of self-assembled molecules as the hole-transporting layer without annealing. This work finally combines the methods to create fully annealing-free devices having stabilized PCEs of up to 17.1%. This represents the state-of-the-art for annealing-free fabrication of PSCs with a process fully compatible with roll-to-roll manufacture.

We have constructed convertible RP (4AEPy)₂PbI₄ and DJ (4AEPy)PbI₄ perovskite with one organic amine through a protonation control strategy. Organic cations in (4AEPy)PbI₄ participate in band edge construction, making its exciton binding energy as low as 27.3 meV and producing more free carriers.

Abstract

The diversity of organic cations greatly enriches the species of 2D perovskites; traditional 2D Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) perovskites are synthesized by two different organic amines. Here, according to the difference in pKa values between conjugated acids of monoprotonated and biprotonated 4-(2-Aminoethyl)pyridine (4AEPy) ions, the 2D perovskites of RP (4AEPy)₂PbI₄ and DJ (4AEPy)PbI₄ from same organic amine is reported, which can realize reversible transformation under the treatment of HI and NH₃, respectively. The interaction of N-H···N hydrogen bond between adjacent organic molecules in (4AEPy)₂PbI₄ leads to the bending conformation of ethylamine groups, which results in a 2.4 Å reduction in layer spacing compared to typical phenylethylamine lead iodine ((PEA)₂PbI₄) 2D perovskite. Besides, the ethylamine groups of organic layers in (4AEPy)PbI₄ are deeply inserted into octahedral cavities and directly participate in the construction of the conduction band minimum, which leads to a small exciton binding energy of 27.3 meV to generate free charges. The stronger coupling between the organic and inorganic layers and the minor exciton binding energy can promote the DJ phase to possess a more stable structure and better optoelectronic properties. Thus the (4AEPy)PbI₄ device displays better light response and X-ray detection capability with a high sensitivity of 5627 µC Gy_air ^-1 cm^-2 and the lowest detectable dose rate of 20 nGy_air s^-1.