Chen Weijie

This study utilized a metal-induced supersaturation-suppression layer (SSL) as a novel interfacial layer to regulate the crystallization dynamics and defect passivation in perovskite solar cells (PSCs). Through metal–halide ion reactions, SSL enhances crystallization kinetics, yielding enlarged perovskite grains and generating chemical adducts that reduce crystalline defects and non-radiative recombination, achieving the development of high-performance PSCs with robust operational stability.

Tailoring crystal growth and defects in perovskites, a viable strategy for suppressing non-radiative recombination, is widely employed for developing efficient and stable perovskite solar cells (PSCs). However, simultaneous tailoring of crystal growth and defects in PSCs is challenging owing to several limitations; for example, excessive interactions between additives and perovskite precursors impede crystallization, and additive-induced impurity phases can substantially increase the defect density in perovskite films. In this study, we introduced a metal-induced supersaturation-suppression layer (SSL) as a pseudo-additive interfacial layer to tailor the crystallization dynamics and defect formation in perovskite crystals in steps. The proposed perovskite modification process involves an SSL-induced metal–halide ion reaction, which modulates the crystallization kinetics for grain growth and enables the formation of metal–halide complex anion adducts that can reduce crystalline defects and suppress non-radiative recombination while facilitating preferential perovskite crystal growth by alleviating residual strains. Because of these stepwise synergistic effects, the SSL-based PSCs exhibited significantly improved device performances (23.4%), low hysteresis losses, and enhanced atmospheric operational stability.

This study explores the impact of bifunctional ligands on optoelectronic properties of 2D perovskites. A strong correlation between electronic gap and Pb─I─Pb bond angle is observed for ─CN, ─COOH, ─Ph, and ─CH₃ based perovskites. The unique and different behavior of the ─OH based compound is attributed to strong interlayer electronic coupling, highlighting the complex role of ligands on 2D perovskites.

Abstract

2D Ruddlesden–Popper metal-halide perovskites exhibit structural diversity due to a variety of choices of organic ligands. Incorporating bifunctional ligands in such materials is particularly intriguing since it can result in novel electronic properties and functions. However, an in-depth understanding of the effects of bifunctional ligands on perovskite structures and, consequently, their electronic and excitonic properties, is still lacking. Here, n = 1 2D perovskites built with organic ligands containing ─CN, ─OH, ─COOH, ─phenyl (Ph), and ─CH₃ functional groups are investigated using ultraviolet and inverse photoemission spectroscopies, density functional theory calculations, and tight-binding model analyses. The experimentally determined electronic gaps of the ─CN, ─COOH, ─Ph, and ─CH₃ based perovskites exhibit a strong correlation with the in-plane Pb─I─Pb bond angle, while the ─OH based perovskite deviates from the linear trend. Based on the band structure calculations, this anomaly is attributed to the out-of-plane dispersion, caused predominantly by significant interlayer electronic coupling that is present in ─OH based perovskites. These results highlight the complex and diverse impacts of organic ligands on electronic properties, especially in terms of the involvement of strong interlayer electronic coupling. The impact of the bifunctional ligands on the evolution of the exciton binding energy is also addressed.

Iodination in organic solar cell molecule yields a breakthrough with the non-fullerene acceptor BO-4I, delivering expanded exciton diffusion, improved intra-moiety excitation, and unprecedentedly low non-radiative losses, propelling photovoltaic efficiency forward.

Abstract

Iodination has unlocked new potentials in organic photovoltaics (OPVs). A newly designed and synthesized iodinated non-fullerene acceptor, BO-4I, showcases exceptional excitation delocalization property with the exciton diffusion length increased to 80 nm. The enhanced electron delocalization property is attributed to the larger atomic radius and electron orbit of the iodine atom, which facilitates the formation of intra-moiety excitations in the acceptor phase. This effectively circumvents the charge transfer state-related recombination mechanisms, leading to a substantial reduction in non-radiative energy loss (ΔE _nr). As a result, OPV cell based on PBDB-TF : BO-4I achieves an impressive efficiency of 18.9 % with a notable ΔE _nr of 0.189 eV, markedly surpassing their fluorinated counterparts. This contribution highlights the pivotal role of iodination in reducing energy loss, thereby affirming its potential as a key strategy in the development of advanced next-generation OPV cells.

Publication date: April 2024

Source: Journal of Energy Chemistry, Volume 91

Author(s): Haikuo Guo, Fuhua Hou, Xuli Ning, Xiaoqi Ren, Haoran Yang, Rui Liu, Tiantian Li, Chengjun Zhu, Ying Zhao, Wei Li, Xiaodan Zhang

Perovskite solar cells (PSCs) always face the issue of open circuit voltage loss (V_loss ). In this review, the principle of reducing V_loss is discussed theoretically, combing a large number of experiments, three feasible technical paths to reduce V_loss are divided from the perspective of Interface Engineering. A summary of the past research and outlooks for a bright future is stated at the end.

Abstract

In recent years, perovskite solar cells (PSCs) have attracted significant attention due to their excellent photoelectric properties. However, several key performance parameters of these devices still fall short of their theoretical limits. Among these parameters, the regulation of open-circuit voltage (V _OC) has been a focal point of intensive research efforts, playing a pivotal role in advancing the efficiency of PSCs. This review first provides an overview of the generation and loss mechanism of V _OC. It then discusses the significance of interface engineering in V _OC regulation. Recent developments in high-efficiency PSCs realized via interface engineering have been summarized and categorized into three key areas: surface modification, interface structure optimization, and surface dimensional engineering. Finally, a comprehensive summary of past research in this domain and offered insights into the future prospects of enhancing V _OC in PSCs is provided.

A heterointerface energetics regulation strategy by introducing potassium trifluoroacetate in the perovskite precursor solution to eliminate the trap defects and optimize surface potential and Fermi level, is proposed. Utilizing TOF-SIMS, potassium is challenging to dope into the perovskite lattice but accumulates at both the upper surface and buried interface of the perovskite for reducing V _OC losses of perovskite solar cells.

Abstract

In the domain of perovskite photovoltaics, the heterointerfaces are subject to substantial trap-assisted non-radiative recombination, predominantly attributed to the energy offset, interface defects, and the roughness of the contact. This phenomenon at the heterointerfaces, where carrier non-radiative recombination and energy dissipation occur due to defects and suboptimal energy level alignment, can be principally held accountable for the V _oc losses. Herein, a heterointerface energetics regulation (HER) strategy is proposed by introducing potassium trifluoroacetate (KTFA) in the perovskite precursor solution to eliminate the trap defects and optimize surface potential and Fermi level. It is first demonstrated that non-doping K⁺ but precipitating at the upper and buried perovskite will improve energy-level alignment for charge extraction dynamics. In addition, the TFA⁻ exhibits strong electrostatic force with undercoordinated Pb²⁺ in the buried contact of perovskite and Sn⁴⁺ in the SnO₂ electron transporting layer. Based on the vacuum flash evaporation green treatment without anti-solvent, the Rb_0.02(Cs_0.05FA_0.95)_0.98PbI_0.91Br_0.03Cl_0.06 and Cs_0.05FA_0.95PbI₃ based device can achieve maximum efficiency of 23.36% and 24.48%, respectively. Further, the modified devices exhibit 92% initial efficiency output after 1200 h of aging. HER strategy for addressing interface defects and bandgap alignment are poised to advance both the performance and stability of perovskite solar cells.

Phosphorylcholine chloride and Me-4PACz are used to form Co-SAM on the NiO _x surface to optimize the buried interface in PSCs. Co-SAM can promote the growth of perovskite crystals, passivate buried defects, optimize the energy band alignment, and relieve the residual stress of the perovskite film, leading to power conversion efficiencies as high as 25.09% and excellent device stability.

Abstract

[4-(3,6-dimethyl-9H-carbazol-9yl)butyl]phosphonic acid (Me-4PACz) self-assembled molecules (SAM) are an effective method to solve the problem of the buried interface of NiO _x in inverted perovskite solar cells (PSCs). However, the Me-4PACz end group (carbazole core) cannot forcefully passivate defects at the bottom of the perovskite film. Here, a Co-SAM strategy is employed to modify the buried interface of PSCs. Me-4PACz is doped with phosphorylcholine chloride (PC) to form a Co-SAM to improve the monolayer coverage and reduce leakage current. The phosphate group and chloride ions (Cl⁻) in PC can inhibit NiO _x surface defects. Meantime, the quaternary ammonium ions and Cl⁻ in PC can fill organic cations and halogen vacancies in the perovskite film to enable defects passivation. Moreover, Co-SAM can promote the growth of perovskite crystals, collaboratively solve the problem of buried defects, suppress nonradiative recombination, accelerate carrier transmission, and relieve the residual stress of the perovskite film. Consequently, the Co-SAM modified devices show power conversion efficiencies as high as 25.09% as well as excellent device stability with 93% initial efficiency after 1000 h of operation under one-sun illumination. This work demonstrates the novel approach for enhancing the performance and stability of PSCs by modifying Co-SAM on NiO _x .

Publication date: April 2024

Source: Journal of Energy Chemistry, Volume 91

Author(s): Jianru Wang, Dan Zhou, Zhentian Xu, Yujie Pu, Senmei Lan, Fang Wang, Feiyan Wu, Bin Hu, Yongfen Tong, Ruizhi Lv, Honglin Chu, Lie Chen

A 2D/3D infiltrated heterojunction is prepared by allowing the 2D perovskite to infiltrate the 3D perovskite surface along the grain boundaries using the interaction between the organic cation of the 2D perovskite and the pseudohalogen thiocyanate ion (SCN^-). The device exhibits a high PCE of 24.76%(certified 24.29%)with V_oc of 1.17V due to both the hydrophobic LD perovskites and the release of residual stresses associated with grain boundary repair.

Abstract

In inverted perovskite solar cells, conventional planar 2D/3D perovskite heterojunctions typically exhibit a type-II band alignment, where the electric field tends to drive the electron motion in the opposite direction to the direction of electron transfer. Here, a 2D/3D gradient heterojunction is developed by allowing the 2D perovskite to infiltrate the 3D perovskite surface along the grain boundaries using the interaction between the organic cation of the 2D perovskite and the pseudohalogen thiocyanate ion (SCN⁻), which has the ability to diffuse downward. The infiltrated 2D perovskite not only fills the gaps of grain boundaries with improved structural stability, but it also reconstructs the original landscape of the electric field toward the n-doped surface to enable more rapid electron transfer and weaken the adverse type-II band alignment effect. Since 2D perovskite seals the GBs, the nonvolatile SCN⁻ can accumulate at the top and bottom dual interfaces, releasing residual stress and significantly inhibiting nonradiative recombination. The device exhibits an excellent efficiency of 24.76% (certified 24.29%) and long-term stability that is >90% of the original PCE value after 800 h of heating at 85 °C or in high humidity (≈65%).

An efficient and universal post-synthetic interstitial Zn²⁺ doping strategy is provided to modify recent popular 3D/2D perovskites, resulting in a champion efficiency of 22.90 % for Zn²⁺-modified 3D/2D PSCs with extended lifespan.

Abstract

Perovskite solar cells (PSCs) have experienced exceptional development in recent years, due to their outstanding photoelectronic properties and low-cost solution processing. Many state-of-the-art PSC designs have been effectively demonstrated using a stacked 3D perovskite/2D perovskite heterostructure, yet limitations arise due to the low conductivity of the 2D perovskite, the hidden buried interface of 3D perovskite, and halide ion migration within 3D/2D PSC device under operational bias. Here, these limitations are overcome by developing a novel and universal post-synthetic metal (Zn²⁺) doping strategy and realizing 3D/2D PSCs with superior efficiency and stability. Informed by ab initio calculations and synchrotron fine structure experiments, it is revealed that the introduced zinc ions are energetically favored at interstitial crystal sites, subsequently hindering the migration of halide ions and producing a beneficial shift toward a more n-type character in the buried 3D perovskite interface. Combined with extensive photophysical characterization, the Zn²⁺-modified 3D/2D perovskite thin film is shown to strongly recover its photo-carrier conductivity compared with the 3D/2D perovskite film, boosting the efficiency (22.90%) of PSCs while exhibiting improved humidity and operational stability.

Two DTBDT-based polymers, PE64 and PE65, are utilized as hole transport materials for low voltage loss CsPbI₂Br perovskite solar cells (PSCs). The CsPbI₂Br PSCs employing PE65 with chlorinated thiophene side chain on the DTBDT unit as hole transport layer achieve a PCE of 17.60 % with a high V _OC of 1.44 V.

Abstract

The power conversion efficiency (PCE) of CsPbI₂Br perovskite solar cells (PSCs) is still far from the theoretical efficiency due to the pronounced losses in open-circuit voltage (V _OC). The V _OC loss can be mitigated by employing an appropriate hole transport layer (HTL), which facilitates energy level alignment and minimizes interface recombination losses. In this work, two D-π-A type polymers are chosen, PE64 and PE65, as HTLs, where pentacyclic dithieno[2,3-d; 2′,3′-d “]benzo[1,2-b; 4,5-b”]dithiophene (DTBDT) as the D-unit and quinoxaline (Qx) as the A-unit. It is demonstrated that the polymer PE65 with chlorinated thiophene side chain on the DTBDT unit has an optimized molecular arrangement, improved energy level matching, and enhanced passivation with CsPbI₂Br, effectively reducing the losses caused by radiative and non-radiative recombination in CsPbI₂Br PSCs. Finally, the CsPbI₂Br PSCs utilizing PE65 as HTL achieve a power conversion efficiency (PCE) of 17.60% with a high V _OC of 1.44 V. Furthermore, the PE64 and PE65 are also employed to construct inter-connecting layers (ICLs) for tandem solar cells (TSCs). The CsPbI₂Br/D18:Y6 TSCs based on PE65-ICL yield a PCE of 22.32% with a high V _OC of 2.25 V. This work demonstrates that pentacyclic DTBDT-based polymers are also promising HTLs for high-performance PSCs and TSCs.

The oligothiophene additives exhibit strong interactions with both the non-fullerene acceptors and the polymer donor, enhancing molecular stacking and promoting favorable phase separation. These effects result in improved charge mobility and reduced recombination, ultimately leading to a promising power conversion efficiency of 18.1% in PM6:Y6-based organic solar cells.

Abstract

Tuning the morphology through processing additives represents one of the most promising strategies to boost the performance of organic solar cells (OSCs). However, it remains unclear how oligothiophene-based solid additives influence the molecular packing and performance of OSCs. Here, two additives namely 2T and 4T, are introduced into state-of-the-art PM6:Y6-based OSCs to understand how they influence the film formation process, nanoscale morphology, and the photovoltaic performance. It is found that the 2T additive can improve the molecular packing of both donor polymer and non-fullerene acceptor, resulting in lower Urbach energy and reduced energy loss. Furthermore, the blend film with 2T treatment displays enhanced domain purity and a more favorable distribution of the acceptor and donor materials in the vertical direction, which can enhance charge extraction efficiency while simultaneously suppressing charge recombination. Consequently, OSCs processed with 2T additive realize a promising efficiency of 18.1% for PM6:Y6-based devices. Furthermore, the general applicability of the additive is demonstrated, and an impressive efficiency of 18.6% for PM6:L8-BO-based OSCs is achieved. These findings highlight that the uncomplicated oligothiophenes have excellent potential in fine-adjustment of the active layer morphology, which is crucial for the future development of OSCs.

To simultaneously control crystallization and reduce the occurrence of deep and shallow-level defects in perovskite films, a highly conductive organometallic compound called 1-propanol-2-(1,2,3-triazol-4-yl) cobaltocenium hexafluorophosphate (PTCoPF₆) is introduced into the perovskite precursor solution. By incorporating PTCoPF₆, the resulting inverted device demonstrates exceptional stability and achieves a remarkable efficiency of 25.03%.

Abstract

Numerous deep/shallow level defects generated at the surface/grain boundaries of perovskite during uncontrollable crystallization pose a formidable challenge to the photovoltaic performance of perovskite solar cells (PSCs). Herein, an organometallic cobaltocenium salt additive, 1-propanol-2-(1,2,3-triazol-4-yl) cobaltocenium hexafluorophosphate (PTCoPF₆), is incorporated into the perovskite precursor solution to regulate crystallization and minimize holistic defects for high-performance inverted PSCs. The cobaltocenium cations and PF₆ ⁻ in PTCoPF₆ stabilize the Pb-I framework and repair the shallow-level defects of positively and negatively charged vacancies in the perovskite. The N═N in the triazole ring of PTCoPF₆ can passivate the deep-level defects of uncoordinated lead. The interaction between PTCoPF₆ and perovskite materials delays perovskite nucleation and crystal growth, ensuring high-quality perovskite with large grains, and suppressing non-radiative recombination and ion migration. Therefore, the PTCoPF₆-incorporated PSC achieves an impressive power conversion efficiency of 25.03% and outstanding long-term stability. Unencapsulated and encapsulated PTCoPF₆-incorporated PSCs maintain 93% and 95% of their initial efficiencies under 85 °C storage in a nitrogen atmosphere for 1000 h and maximum power point tracking for nearly 1000 h, respectively. Synergistic crystallization kinetic modulation and deep/shallow level defect passivation with ionized metal-organic complex additives will become prevalent methods to improve the efficiency and stability of PSCs.

A selective grain boundary (GB) passivation strategy for 4,4'-diaminodiphenylsulfone (DDS) and 4,4'-sulfonyldiphenol (SDP) driven by solvation, which not only passivate the uncoordinated Pb²⁺ in GBs, but also optimize the energy level arrangement through the electric dipole effect. Consequently, the SDP-modified device exhibits significant improvements, including a champion efficiency of 24.39% and an impressive fill factor, along with excellent operation stability.

Abstract

The efficiency of perovskite solar cells (PSCs) is hindered by substantial defects within the grain boundaries (GBs) of polycrystalline perovskite films. Conventional post-treatment strategies struggle to precisely repair these defects at GBs. Here, a targeted grain boundary passivation strategy through solvent effects by incorporating symmetrical biphenyl molecules is proposed, 4,4′-diaminodiphenyl sulfone (DDS) and 4,4′-sulfodiphenol (SDP), aiming to mitigate defects at GBs and optimize energy level arrangements through their electric dipole effects. Compared to the pristine device, the SDP-modified device exhibits significant improvements, including a champion efficiency of 24.39% and an impressive fill factor, along with excellent operation stability. This work provides an effective and straightforward solution for improving the performance of PSCs.

A brand-new chelating strategy using sodium diethyldithiocarbamate to strongly coordinate with undercoordinated metal cations on the surface of Cu₂ZnSn(S,Se)₄ (CZTSSe) films is demonstrated. The power conversion efficiency is significantly increased to 13.77%, making it one of the most efficient CZTSSe solar cells. This surface chelation strategy provides strong surface termination and defect passivation for further development and application of kesterite-type photovoltaic device.

Abstract

Surfaces display discontinuities in the kesterite-based polycrystalline films can produce large defect densities, including strained and dangling bonds. These physical defects tend to introduce electronic defects and surface states, which can greatly promote nonradiative recombination of electron–hole pairs and damage device performance. Here, an effective chelation strategy is reported to suppress these harmful physical defects related to unterminated Cu, Zn, and Sn sites by modifying the surface of Cu₂ZnSn(S,Se)₄ (CZTSSe) films with sodium diethyldithiocarbamate (NaDDTC). The conjoint theoretical calculations and experimental results reveal that the NaDDTC molecules can be coordinate to surface metal sites of CZTSSe films via robust bidentate chelating interactions, effectively reducing surface undercoordinated defects and passivating the electron trap states. Consequently, the solar cell efficiency of the NaDDTC-treated device is increased to as high as 13.77% under 100 mW cm⁻² illumination, with significant improvement in fill factor and open-circuit voltage. This surface chelation strategy provides strong surface termination and defect passivation for further development and application of kesterite-based photovoltaics.

Nature Energy, Published online: 09 January 2024; doi:10.1038/s41560-023-01436-z

The donor/acceptor interface structures and features show an obvious influence on blending phase-separation morphology and charge transport behavior. It is not reasonable to simply judge the quality of fluorinated and chlorinated acceptors without suitable selection of donors, and regulating donor/acceptor interfaces can accurately present the photoelectric conversion ability of a novel acceptors.

Abstract

End-groups halogenation strategies, generally refers to fluorination and chlorination, have been confirmed as simple and efficient methods to regulate the photoelectric performance of non-fullerene acceptors (NFAs), but a controversy over which one is better has existed for a long time. Here, two novel NFAs, C9N3-4F and C9N3-4Cl, featured with different end-groups were successfully synthesized and blended with two renowned donors, D18 and PM6, featured with different electron-withdrawing units. Detailed theoretical calculations and morphology characterizations of the interface structures indicate NFAs based on different end-groups possess different binding energy and miscibility with donors, which shows an obvious influence on phase-separation morphology, charge transport behavior and device performance. After verified by other three pairs of reported NFAs, a universal conclusion obtained as the devices based on D18 with fluorination-end-groups-based NFAs and PM6 with chlorination-end-groups-based NFAs generally show excellent efficiencies, high fill factors and stability. Finally, the devices based on D18: C9N3-4F and PM6: C9N3-4Cl yield outstanding efficiency of 18.53 % and 18.00 %, respectively. Suitably selecting donor and regulating donor/acceptor interface can accurately present the photoelectric conversion ability of a novel NFAs, which points out the way for further molecular design and selection for high-performance and stable organic solar cells.

Nature Materials, Published online: 09 January 2024; doi:10.1038/s41563-023-01771-2

An ion-alloying strategy is reported to inhibit phase segregation in wide-bandgap perovskites by doping RbCl. Based on this strategy, a high steady-state power conversion efficiency (PCE) of 24.48% from perovskite/perovskite/c-Si triple-junction tandem is achieved, a giant leap from the previous PCE record and the highest certified efficiency among all types of perovskite-based triple-junction tandem solar cells.

Abstract

Wide-bandgap metal halide perovskites have demonstrated promise in multijunction photovoltaic (PV) cells. However, photoinduced phase segregation and the resultant low open-circuit voltage (V _oc) have greatly limited the PV performance of perovskite-based multijunction devices. Here, a alloying strategy is reported to achieve uniform distribution of triple cations and halides in wide-bandgap perovskites by doping Rb⁺ and Cl⁻ with small ionic radii, which effectively suppresses halide phase segregation while promoting the homogenization of surface potential. Based on this strategy, a V _oc of 1.33 V is obtained from single-junction perovskite solar cells, and a V _OC approaching 3.0 V and a power conversion efficiency of 25.0% (obtained from reverse scan direction, certified efficiency: 24.19%) on an 1.04 cm² photoactive area can be achieved in a perovskite/perovskite/c-Si triple-junction tandem cell, where the certification efficiency is by far the greatest performance of perovskite-based triple-junction tandem solar cells. This work overcomes the performance deadlock of perovskite-based triple-junction tandem cells by setting a materials-by-design paradigm.

In this work, an ultra-thin zinc nitride (Zn₃N₂) layer is introduced on the NiO_x surface is chosen to prevent these redox reactions and interfacial issues using a simple solution process at low temperatures. The redox reaction and non-radiative recombination at the interface of the perovskite and NiO_x reduce chemically by using interface modifier Zn₃N₂ to reduce hydroxyl group and defects on the surface of NiO_x. A thin layer of Zn₃N₂ at the NiO_x/perovskite interface results in a high Ni³⁺/Ni²⁺ ratio and a significant work function (WF), which inhibits the redox reaction and provides a highly aligned energy level with perovskite crystal and rigorous trap-passivation ability. Consequently, Zn₃N₂-modified NiO_x-based PSCs achieve a champion PCE of 21.61%, over the NiO_x-based PSCs. After Zn₃N₂ modification, the PSC can improve stability under several conditions.

Abstract

For p-i-n perovskite solar cells (PSCs), nickel oxide (NiO_x) hole transport layers (HTLs) are the preferred interfacial layer due to their low cost, high mobility, high transmittance, and stability. However, the redox reaction between the Ni^≥3+ and hydroxyl groups in the NiO_x and perovskite layer leads to oxidized CH₃NH₃ ⁺ and reacts with PbI in the perovskite, resulting in a large number of non-radiative recombination sites. Among various transition metals, an ultra-thin zinc nitride (Zn₃N₂) layer on the NiO_x surface is chosen to prevent these redox reactions and interfacial issues using a simple solution process at low temperatures. The redox reaction and non-radiative recombination at the interface of the perovskite and NiO_x reduce chemically by using interface modifier Zn₃N₂ to reduce hydroxyl group and defects on the surface of NiO_x. A thin layer of Zn₃N₂ at the NiO_x/perovskite interface results in a high Ni³⁺/Ni²⁺ ratio and a significant work function (WF), which inhibits the redox reaction and provides a highly aligned energy level with perovskite crystal and rigorous trap-passivation ability. Consequently, Zn₃N₂-modified NiO_x-based PSCs achieve a champion PCE of 21.61%, over the NiO_x-based PSCs. After Zn₃N₂ modification, the PSC can improve stability under several conditions.

A bottom-up multilayer manipulation strategy is proposed by pre-embedding multisite racemic DL-cysteine hydrochloride monohydrate (DLCH) into SnO₂ electron transport layer. The synergy of multiple functional groups and multiple chemical bonds enables bottom-up cross-layer passivation, which minimizes bulk and interfacial nonradiative recombination losses. The power conversion efficiency is improved from 21.61 to 24.01% after DLCH modulation.

Abstract

The defects from functional layers and interface, the agglomeration of SnO₂ nanoparticles (NPs), and poor perovskite crystallization are the main barrier to further heightening the power conversion efficiency (PCE) and stability of regular perovskite solar cells. Here, a bottom-up multilayer manipulation strategy by pre-embedding multisite racemic DL-cysteine hydrochloride monohydrate (DLCH) into the SnO₂ electron transport layer (ETL) is reported. The positively and negatively charged defects from ETL, perovskite layer and their interface can be passivated through the synergistic effect of the ─SH, ─COOH, ─NH₃ ⁺, and Cl⁻ groups in DLCH. The synergy of multiple functional groups and multiple chemical bonds enables bottom-up cross-layer passivation, which minimizes bulk and interfacial nonradiative recombination losses. Furthermore, the multifunctional DLCH plays a role in inhibiting the agglomeration of SnO₂ NPs, managing photons, relieving interfacial tensile stress, and manipulating perovskite crystallization. Benefiting from the above advantages, the DLCH-incorporating device delivers a PCE of 24.01%, which is much higher than the 21.61% of the control device. Moreover, the DLCH-modified devices demonstrate inviting thermal and ambient stabilities by maintaining 93% of the initial efficiency after aging at 65 °C for 1800 h and 95% of the original PCE after aging under a relative humidity of 20–25% for 2000 h.

Utilizing in situ monitoring techniques to optimize the crystallization kinetics of the perovskite films in the gas-quenching-assisted blade coating process, a champion power conversion efficiency of 19.50% for a fully printed carbon-electrode perovskite solar cell is achieved through the tailored control of crystal growth rates.

Abstract

The pursuit of commercializing perovskite photovoltaics is driving the development of various scalable perovskite crystallization techniques. Among them, gas quenching is a promising crystallization approach for high-throughput deposition of perovskite films. However, the perovskite films prepared by gas-quenching assisted blade coating are susceptible to the formation of pinholes and frequently show inferior crystallinity if the interplay between film coating, film drying, and crystallization kinetics is not fully optimized. That arguably requires a thorough understanding of how single processing steps influence the crystallization kinetics of printed perovskite films. Here, in situ optical spectroscopies are integrated into a doctor-blading setup that allows to real-time monitor film formation during the gas-quenching process. It is found that the essential role of gas quenching treatment is in achieving a smooth and compact perovskite film by controlling the nucleation rate. Moreover, with the assistance of phase-field simulations, the role of excessive methylammonium iodide is revealed to increase grain size by accelerating the crystal growth rate. These results show a tailored control of crystal growth rate is critical to achieving optimal film quality, leading to fully printed solar cells with a champion power conversion efficiency of 19.50% and mini solar modules with 15.28% efficiency are achieved.

A porous nanoparticle layer is inserted between the ITO and perovskite layer to form occlusal architecture, leading to improved interfacial adhesion. Ultimately the flexible perovskite devices show enhanced mechanical reliability against bending.

Abstract

Flexible perovskite photovoltaic cells (f-PPCs) have demonstrated enormous potential in portable electronics due to the high power-to-weight ratio characteristic in outdoor and indoor ambient environment. However, the inherent mechanical endurance of f-PPCs remains a major concern. Inspired by industrial strong adhesion coatings, herein, a porous nanoparticle layer is inserted into the buried interface of the perovskite layer to regulate the interfacial adhesion with a smooth hole transporting layer (HTL). As a result, the f-PPCs realizes retaining over 80% of original efficiency after 2000 in-plane bending cycles with the narrow radius of 4 mm. Furthermore, a certified record efficiency of 20.20% is achieved for flexible perovskite solar module, as well as the record efficiency of 31.69% for flexible perovskite indoor photovoltaic module (LED, 1000 lux).

1-aza-15-crown 5-ether (A15C5), with a unique nitrogen heterocyclic structure as a supramolecular modulator is introduced at the interface between perovskite and hole transport layer. Synergistic interaction between A15C5 and perovskite suppresses defects. The formation of two-dimensional/three-dimensionals perovskite induced by planar A15C5 releases residual strain and adjusts the energy level array. A15C5-modulated PSC achieves an impressive efficiency of 24.13% along with excellent humidity, light, and thermal stability.

Abstract

Molecular modulators have been demonstrated to be an effectual strategy for reducing the defect at the interface and in bulk of perovskite and ameliorating the performance and stability of perovskite solar cells (PSCs). Herein, 1-aza-15-crown 5-ether (A15C5), with a unique nitrogen heterocyclic structure as a molecular modulator is introduced at the interface between perovskite layer and hole transport layer of PSCs. Multiple supramolecular synergistic interaction between A15C5 and perovskite dramatically suppress and passivate defects, resulting in a 38% decrease in electron trap-state density in perovskite. The formation of two-dimensional/th3D perovskite heterojunctions induced by planar A15C5 releases residual strain of perovskite film, optimizes the match of energy level array and boosts the stability of devices. Consequently, A15C5-modulated PSC achieves an impressing efficiency of 24.13% along with excellent humidity, light and thermal stability. This work provides a typical strategy to utilize supramolecular crown ether in PSCs.

In this work, a 3D framework formed by spontaneous cross-linking is introduced in perovskite precursor to increase their viscosity and homogenize their heat diffusion coefficient. As a result, the Marangoni convection intensity during meniscus printing is properly controlled, thus ensuring the deposition of high-quality perovskite films and significantly enhancing the reproducibility in printing efficient photovoltaics by mitigating the coffee-ring effect.

Abstract

Organic–inorganic hybrid perovskites are considered ideal candidates for future photovoltaic applications due to their excellent photovoltaic properties. Although solution-printed manufacturing has shown inherent potential for the low-cost, high-throughput production of thin-film semiconductor electronics, the high-quality and high-reproducibility deposition of large-area perovskite remains a bottleneck that restricts their commercialization due to the droplet coffee-ring effect (CRE). In this study, these issues are addressed by introducing an in situ polymer framework. The 3D framework formed by spontaneous cross-linking improves the precursor viscosity and homogenizes its heat diffusion coefficient, counteracting the lateral capillary flow of the colloidal particles and anchoring their flocculent movement. Thus, the Marangoni convection intensity is properly controlled to ensure high-quality perovskite films, which significantly enhances reproducibility in printing efficient photovoltaics by mitigating the CRE. Subsequently, the perovskite solar cells and modules achieve power conversion efficiencies of 23.94 and 17.53%, and exhibit positive environmental stability, retaining over 90 and 78% efficiency after storage for 2500 and 1600 h, respectively. This work may serves as a foundation for exploring precursor rheology to match the homogeneous deposition requirements of perovskite photovoltaics and facilitating the advancement of their printing manufacturing and commercialization transition.

Deuteration strategy is proposed to reduce molecular vibrational frequency and inhibit exciton-vibration coupling to decrease the non-radiative decay rate for prolonged exciton lifetime (τ). The deuterated L8-BO-D affords an excellent τ of 1.35 ns (the record for organic photovoltaic materials) to realize the improved L _D of 10.7 nm. Benefiting from the prolonged L _D, organic solar cells based on L8-BO-D achieve an impressive PCE of 19.3 %.

Abstract

The limited exciton lifetime (τ, generally <1 ns) leads to short exciton diffusion length (L _D) of organic semiconductors, which is the bottleneck issue impeding the further improvement of power conversion efficiencies (PCEs) for organic solar cells (OSCs). However, efficient strategies to prolong intrinsic τ are rare and vague. Herein, we propose a facile method to efficiently reduce vibrational frequency of molecular skeleton and suppress exciton-vibration coupling to decrease non-radiative decay rate and thus prolong τ via deuterating nonfullerene acceptors. The τ remarkably increases from 0.90 ns (non-deuterated L8-BO) to 1.35 ns (deuterated L8-BO-D), which is the record for organic photovoltaic materials. Besides, the inhibited molecular vibration improves molecular planarity of L8-BO-D for enhanced exciton diffusion coefficient. Consequently, the L _D increases from 7.9 nm (L8-BO) to 10.7 nm (L8-BO-D). The prolonged L _D of L8-BO-D enables PM6 : L8-BO-D-based bulk heterojunction OSCs to acquire higher PCEs of 18.5 % with more efficient exciton dissociation and weaker charge carrier recombination than PM6 : L8-BO-based counterparts. Moreover, benefiting from the prolonged L _D, D18/L8-BO-D-based pseudo-planar heterojunction OSCs achieve an impressive PCE of 19.3 %, which is among the highest values. This work provides an efficient strategy to increase the τ and thus L _D of organic semiconductors, boosting PCEs of OSCs.

A polydentate ligand reinforced chelating strategy is proposed to strengthen the stability of buried interface by managing interfacial defects and stress. The BTP-modified device achieves a promising power conversion efficiency (PCE) of 24.63 %. The unencapsulated BTP-modified devices degrade to 98.6 % and 84.2 % of their initial PCE values after over 3000 h of aging in the ambient environment and after 1728 h of thermal stress, respectively.

Abstract

The instability of the buried interface poses a serious challenge for commercializing perovskite photovoltaic technology. Herein, we report a polydentate ligand reinforced chelating strategy to strengthen the stability of buried interface by managing interfacial defects and stress. The bis(2,2,2-trifluoroethyl) (methoxycarbonylmethyl)phosphonate (BTP) is employed to manipulate the buried interface. The C=O, P=O and two −CF₃ functional groups in BTP synergistically passivate the defects from the surface of SnO₂ and the bottom surface of the perovskite layer. Moreover, The BTP modification contributes to mitigated interfacial residual tensile stress, promoted perovskite crystallization, and reduced interfacial energy barrier. The multidentate ligand modulation strategy is appropriate for different perovskite compositions. Due to much reduced nonradiative recombination and heightened interface contact, the device with BTP yields a promising power conversion efficiency (PCE) of 24.63 %, which is one of the highest efficiencies ever reported for devices fabricated in the air environment. The unencapsulated BTP-modified devices degrade to 98.6 % and 84.2 % of their initial PCE values after over 3000 h of aging in the ambient environment and after 1728 h of thermal stress, respectively. This work provides insights into strengthening the stability of the buried interface by engineering multidentate chelating ligand molecules.

Nature Materials, Published online: 05 January 2024; doi:10.1038/s41563-023-01759-y