Chen Weijie

An in situ dehydration condensation reaction of self-assembled molecule Me-4PACz is observed during the high-temperature annealing process of inorganic perovskites, which leads to enhanced anchoring interaction and more effective hydrophobic protection of CsPbI₃, thus yielding high-quality inorganic perovskite films. Eventually, a high power conversion efficiency of 21.38% is realized, representing a record value for the inverted inorganic perovskite solar cells (PSCs).

Abstract

Inorganic perovskites, with Cs⁺ substituting volatile organic components, show great promise in photovoltaic applications due to their outstanding optoelectronic properties and thermal stability. However, the black-to-yellow phase transition of CsPbI₃ remains a challenge for realizing high-performance inorganic perovskite solar cells (IPSCs). Herein, an effective approach is reported via incorporating the self-assembled molecule Me-4PACz to synergistically stabilize the [PbI₆]⁴⁻ octahedra and form a hydrophobic layer at interface and grain boundaries. An in situ dehydration condensation reaction of Me-4PACz is observed during film annealing, which favors the reduction of undesired aggregation of Me-4PACz in humid air, thus leading to enhanced anchoring interaction and more effective hydrophobic protection of CsPbI₃. Therefore, the air-processed CsPbI₃ perovskite films show dramatically improved phase purity and humid stability. This strategy also improves the energy level alignment between perovskite and charge transport layers. As a result, a champion efficiency of 20.21% is realized, representing one of the highest reported values for air-processed inverted IPSCs. Furthermore, it is demonstrated that by combining Me-4PACz with the previously reported ethacridine lactate (EAL) additive, the device performance can be further boosted to 21.38%, which is a record efficiency for the inverted IPSCs reported to date.

Publication date: October 2024

Source: Nano Energy, Volume 129, Part A

Author(s): Jinpeng Zhou, Chuanhang Guo, Liang Wang, Chen Chen, Zirui Gan, Yuandong Sun, Chenhao Liu, Jing Zhou, Zhenghong Chen, Dawei Gao, Weiyi Xia, Dan Liu, Tao Wang, Wei Li

Publication date: October 2024

Source: Nano Energy, Volume 129, Part A

Author(s): Xiangrong Cao, Xinyi Zhu, Peizhou Li, Ruoyao Xu, Bo Jiao, Zhaoxin Wu, Hua Dong

Electron transport layers prepared by sequential deposition of diluted tin dioxide (SnO₂) dispersion are applied to lead iodide (FAPbI₃) perovskite solar cells (PSCs). This simple method leads to a small roughness, pinhole-free, and high photoconductive SnO₂ layer, and thus improvement in the power conversion efficiency of PSC to ≈23%.

The widespread use of tin dioxide (SnO₂) thin films as electron transport layer (ETL) of perovskite solar cells (PSCs) has been facilitated by commercial SnO₂ nanocolloid dispersion. Nevertheless, challenges such as nanoparticle agglomeration have emerged, impacting film quality and interface properties critical for PSC performance. Herein, the efficacy of sequential, multistep spin-coating of repeatedly diluted SnO₂ aqueous suspension as a simple and effective approach to enhance ETL properties is explored. Through systematic experiments using dynamic light scattering, cyclic voltammetry, optical spectroscopy, and photoconductivity, it is demonstrated that the sequential deposition significantly improves the flatness and coverage of SnO₂, leading to improved electron transport and transfer from a perovskite layer. Such a synergetic effect enables to fabricate lead iodide PSC (FAPbI₃, FA: formamidinium) with a power conversion efficiency of 22.99% compared to 20.48% for the conventional 1-step SnO₂ layer. The findings underscore the potential of sequential SnO₂ deposition as a promising technique for robust SnO₂ films of photoelectric conversion devices.

In this article, ternary organic solar cells (T-OSCs) are fabricated under open-air conditions. The optimized ternary device with 20% DRCTF shows power conversion efficiency of 14.45% with enhanced short-circuit current density, open-circuit voltage, fill factor, and reduced non-radiative ΔV _loss. This efficiency is higher than binary counterpart (12.46%). The design approach can serve as a foundation for future T-OSC advancements.

The structural disorder and aggregation of the third acceptor with the host active layer are critical in the light absorption, film morphology, and charge-carrier mechanism of their photovoltaic blends to achieve highly efficient organic solar cells (OSCs). However, an effective third component needs to be introduced in the host binary blend as a combination of ternary blend, which can improve the absorption profile, film morphology, and charge dynamics. In this work, non-fullerene acceptor DRCTF is incorporated as a third component in host PM6:Y6 binary blend. Compared to host blend, the ternary blend improves charge-transfer processes, as evidenced by steady-state photoluminescence and time-resolved photoluminescence measurements. It is found that the addition of 20% DRCTF into host binary blend results in improved charge dissociation and transport with reduced recombination, and voltage losses. All these characteristics contribute to an improved power conversion efficiency of 14.45% in the PM6:Y6:DRCTF ternary OSCs (T-OSCs), compared to PM6:Y6 (12.46%) in open-air fabrication conditions. Consequently, in this study, the impact of third components on the charge-transfer mechanism in T-OSCs is elucidated. These findings suggested that T-OSCs with a perfectly chosen third component in the host binary blend achieve a comprehensive absorption profile, smooth film morphology, efficient charge dynamics, and reduced voltage loss.

The supersaturated point defects in perovskite films will generate during cooling process after annealing and its concentration improves as the cooling rate increases. These defects can be minimized through slowing the cooling rate. The resultant PSCs deliver a 25.47% PCE (certified 24.7%) and retain >90% of their initial value after >1100 h of operation at the maximum power point.

Abstract

Numerous efforts are devoted to reducing the defects at perovskite surface and/or grain boundary; however, the grown-in defects inside grain is rarely studied. Here, the influence of cooling rate on the point defects concentration in polycrystalline perovskite film during heat treatment processing is investigated. With the combination of theoretical and experimental studies, this work reveals that the supersaturated point defects in perovskite films generate during the cooling process and its concentration improves as the cooling rate increases. The supersaturated point defects can be minimized through slowing the cooling rate. As a result, the optimized FAPbI₃ polycrystalline films achieve a superior carrier lifetime of up to 12.6 µs and improved stability. The champion device delivers a 25.47% PCE (certified 24.7%) and retain 90% of their initial value after >1100 h of operation at the maximum power point. These results provide a fundamental understanding of the mechanisms of grown-in defects formation in polycrystalline perovskite film.

Dipole moment of crown ethers indicates their supramolecular interactions with perovskites. Higher dipole moments enhance coordination with lead cations, improving film morphology and optoelectronic properties. Optimized host–guest complexation led to perovskite solar modules reaching a 21.5 % efficiency over 14.0 cm².

Abstract

Host-guest complexation offers a promising approach for mitigating surface defects in perovskite solar cells (PSCs). Crown ethers are the most widely used macrocyclic hosts for complexing perovskite surfaces, yet their supramolecular interactions and functional implications require further understanding. Here we show that the dipole moment of crown ethers serves as an indicator of supramolecular interactions with both perovskites and precursor salts. A larger dipole moment, achieved through the substitution of heteroatoms, correlates with enhanced coordination with lead cations. Perovskite films incorporating aza-crown ethers as additives exhibited improved morphology, reduced defect densities, and better energy-level alignment compared to those using native crown ethers. We report power-conversion efficiencies (PCEs) exceeding 25 % for PSCs, which show enhanced long-term stability, and a record PCE of 21.5 % for host–guest complexation-based perovskite solar modules with an active area of 14.0 cm².

Publication date: September 2024

Source: Nano Energy, Volume 128, Part B

Author(s): Xin Meng, Xiaoxuan Liu, Qisen Zhou, Zonghao Liu, Wei Chen

The P3HT hole transport layer (HTL) featuring preferable three-dimension molecular orientation is realized via optimizing its preparation process. The preferable molecular orientation of P3HT HTL imparts improved electronic properties, enhanced moisture-repelling capability, intensified defect passivation, and matched energy level. The small-area (0.04 cm²) and large-area (1 cm²) carbon-electrode devices deliver notable efficiency of 20.55% and 18.32% with desirable stability.

Abstract

Carbon-based perovskite solar cells (PSCs) coupled with solution-processed hole transport layers (HTLs) have shown potential owing to their combination of low cost and high performance. However, the commonly used poly(3-hexylthiophene) (P3HT) semicrystalline-polymer HTL dominantly shows edge-on molecular orientation, in which the alkyl side chains directly contact the perovskite layer, resulting in an electronically poor contact at the perovskite/P3HT interface. The study adopts a synergetic strategy comprising of additive and solvent engineering to transfer the edge-on molecular orientation of P3HT HTL into 3D molecular orientation. The target P3HT HTL possesses improved charge transport as well as enhanced moisture-repelling capability. Moreover, energy level alignment between target P3HT HTL and perovskite layer is realized. As a result, the champion devices with small (0.04 cm²) and larger areas (1 cm²) deliver notable efficiencies of 20.55% and 18.32%, respectively, which are among the highest efficiency of carbon-electrode PSCs.

Calculation and experimental results corroborate that the strategic incorporation of 1-butyl-3-methylimidazolium thiocyanate (BmimSCN) resulted in a remarkable enhancement of intrinsic charge transport properties, effective passivation of defects and trap states, and a tunable bandgap, leading to improved optoelectronic characteristics. The altered electronic structure influences crystallization kinetics, resulting in larger, higher-quality crystalline grains and superior photovoltaic performance with a champion power conversion efficiency (PCE) of 15.2%.

Abstract

This study delves into the innovative approach of enhancing the efficiency and stability of all-inorganic perovskite solar cells (I-PSCs) through the strategic incorporation of thiocyanate (SCN⁻) ions via pseudohalide-based ionic liquid (IL) configurations. This straightforward methodology has exhibited captivating advancements in the kinetics of crystallization as well as the optoelectronic characteristics of the resulting perovskite films. These developments hold the promise of enhancing not only the quality and uniformity of the films but also aspects such as band alignment and the efficacy of charge transfer mechanisms. Calculation results corroborate that the incorporation of 1-butyl-3-methylimidazolium thiocyanate (BmimSCN) led to a significant redistribution of electron state density and enhanced electron-donating properties, indicating a substantial electron transfer between the perovskite material and the IL. Notably, the engineered devices demonstrate a remarkable efficiency surpassing 15%, a substantial enhancement attributed to the synergistic effects of the SCN⁻ ion. Additionally, this approach offers inherent stability benefits, thereby addressing a significant challenge in I-PSC technology. This IL maintains >90% of the initial efficiency after 600 h, while the control device decreased to <20% of its initial value after only 100 h. 1-butyl-3-methylimidazolium iodide (BmimI) is also employed to further investigate the effects of SCN⁻ ions on device performance.

Thermal co-evaporation is developed for the deposition of 2D and quasi-2D Ruddlesden-Popper (RP) Interlayers with nanometer control. Compared to untreated devices, thermally evaporated 2D materials on three-dimensional (3D) perovskites show improvement of 2% absolute efficiency reaching close to 22%.

Abstract

Solution-processed Ruddlesden-Popper (RP) interlayers in lead halide perovskite solar cells (PSCs) present processing challenges due to fast film formation and uncontrolled growth of phases and layer thickness at interfaces. In this work, an alternative, solvent-free, thermal co-evaporation process is developed to deposit RP interlayers. The method provides precise control on interlayer thickness and enables understanding its role on charge-carrier extraction. Studying RP film growth reveals the development of heterointerfaces when deposited on three-dimensional (3D) perovskite layers. This allows a large thickness window with an optimum between 20 nm and 40 nm to improve the optoelectronic properties of the underlying 3D perovskite. Solar cells using evaporated interlayers achieve power conversion efficiency of 21.6%, compared to 19.6% for untreated devices, driven by improvements in the open-circuit voltage and fill factor. This work sheds light on the importance of phase and thickness control of passivation layers, which ultimately determine the solar cell performance in state-of-the-art PSCs.

Frenkel and charge-transfer excitonic couplings at donor:acceptor interfaces strengthened by 2-chlorothiophene (2Cl−Th) solvent promote exciton splitting and reduce non-radiative voltage loss in organic solar cells. Finally, in 2Cl−Th treated cells, the champion efficiencies of 19.8 % (small-area) with superior operational reliability (T80: 586 hours) and 17.0 % (large-area) were yielded.

Abstract

Overcoming the trade-off between short-circuited current (J _sc) and open-circuited voltage (V _oc) is important to achieving high-efficiency organic solar cells (OSCs). Previous works modulated the energy gap between Frenkel local exciton (LE) and charge-transfer (CT) exciton, which served as the driving force of exciton splitting. Differently, our current work focuses on the modulation of LE-CT excitonic coupling (t_LE-CT) via a simple but effective strategy that the 2-chlorothiophene (2Cl−Th) solvent utilizes in the treatment of OSC active-layer films. The results of our experimental measurements and theoretical simulations demonstrated that 2Cl−Th solvent initiates tighter intermolecular interactions with non-fullerene acceptor in comparison with that of traditional chlorobenzene solvent, thus suppressing the acceptor's over-aggregation and retarding the acceptor crystallization with reduced trap. Critically, the resulting shorter distances between donor and acceptor molecules in the 2Cl−Th treated blend efficiently strengthen t_LE-CT, which not only promotes exciton splitting but also reduces non-radiative recombination. The champion efficiencies of 19.8 % (small-area) with superior operational reliability (T80: 586 hours) and 17.0 % (large-area) were yielded in 2Cl−Th treated cells. This work provided a new insight into modulating the exciton dynamics to overcome the trade-off between J _sc and V _oc, which can productively promote the development of the OSC field.

Publication date: 21 August 2024

Source: Joule, Volume 8, Issue 8

Author(s): Han Yu, Yan Wang, Chung Hang Kwok, Rongkun Zhou, Zefan Yao, Subhrangsu Mukherjee, Aleksandr Sergeev, Haixia Hu, Yuang Fu, Ho Ming Ng, Li Chen, Di Zhang, Dahui Zhao, Zilong Zheng, Xinhui Lu, Hang Yin, Kam Sing Wong, Harald Ade, Chen Zhang, Zonglong Zhu

Publication date: 18 September 2024

Source: Joule, Volume 8, Issue 9

Author(s): Junyi Xu, Thomas Heumüller, Vincent M. Le Corre, Anastasiia Barabash, Roberto Félix, Johannes Frisch, Marcus Bär, Christoph J. Brabec

Publication date: 18 September 2024

Source: Joule, Volume 8, Issue 9

Author(s): Xiao Guo, Zhenrong Jia, Shunchang Liu, Renjun Guo, Fangyuan Jiang, Yangwei Shi, Zijing Dong, Ran Luo, Yu-Duan Wang, Zhuojie Shi, Jia Li, Jinxi Chen, Ling Kai Lee, Peter Müller-Buschbaum, David S. Ginger, David J. Paterson, Yi Hou

Abietic acid (AA), a soldering flux, is introduced into Sn-Pb perovskite solar cells to tackle complex defects chemistry. The C═C bond within AA continuously eliminates Sn⁴⁺ and Pb⁰ defects, while the presence of C═O bond enhances the antioxidation stability of Sn²⁺. This innovative and effective approach leads to 23.42% power conversion efficiency of Sn-Pb perovskite solar cell.

Abstract

Developing tin-lead (Sn-Pb) narrow-bandgap perovskites is crucial for the deployment of all-perovskite tandem solar cells, which can help to exceed the limits of single-junction photovoltaics. However, the Sn-Pb perovskite suffers from a large number of bulk traps and interfacial nonradiative recombination centers, with unsatisfactory open-circuit voltage and the consequent device efficiency. Herein, for the first time, it is shown that abietic acid (AA), a commonly used flux for metal soldering, effectively tackles complex defects chemistry in Sn-Pb perovskites. The conjugated double bond within AA molecule plays a key role for self-elimination of Sn⁴⁺-Pb⁰ defects pair, via a redox process. In addition, C═O group is able to coordinate with Sn²⁺, leading to the improved antioxidative stability of Sn-Pb perovskites. Consequently, a ten-times longer carrier lifetime is observed, and the defects-associated dual-peak emission feature at low temperature is significantly inhibited. The resultant device achieves a power conversion efficiency improvement from 22.28% (Ref) to 23.42% with respectable stability under operational and illumination situations.

Interface-induced nonradiative recombination losses are significantly limiting the performance improvement in perovskite solar cells (PSCs). A multifunctional dipole molecule modifies the perovskite surface to reduce defects and optimize energy alignment, suppressing the nonradiative recombination. The p-i-n device achieves an improved efficiency that stabilizes under both high humidity and maximum power point tracking.

Abstract

Interface-induced nonradiative recombination losses at the perovskite/electron transport layer (ETL) are an impediment to improving the efficiency and stability of inverted (p-i-n) perovskite solar cells (PSCs). Tridecafluorohexane-1-sulfonic acid potassium (TFHSP) is employed as a multifunctional dipole molecule to modify the perovskite surface. The solid coordination and hydrogen bonding efficiently passivate the surface defects, thereby reducing nonradiative recombination. The induced positive dipole layer between the perovskite and ETLs improves the energy band alignment, enhancing interface charge extraction. Additionally, the strong interaction between TFHSP and the perovskite stabilizes the perovskite surface, while the hydrophobic fluorinated moieties prevent the ingress of water and oxygen, enhancing the device stability. The resultant devices achieve a power conversion efficiency (PCE) of 24.6%. The unencapsulated devices retain 91% of their initial efficiency after 1000 h in air with 60% relative humidity, and 95% after 500 h under maximum power point (MPP) tracking at 35 °C. The utilization of multifunctional dipole molecules opens new avenues for high-performance and long-term stable perovskite devices.

Nature, Published online: 08 July 2024; doi:10.1038/s41586-024-07764-8

Mixed spacer cations [diethylamine (DEA⁺) and phenethylamine (PEA⁺)] favor the formation of homogeneous low-dimensional tin perovskite phases with three octahedral monolayers (n = 3), especially near the bottom interface between perovskite and hole transport layer. The homogenization of 2D phases helps improve the film quality with reduced lattice distortion and released strain.

Abstract

2D-3D tin-based perovskites are considered as promising candidates for achieving efficient lead-free perovskite solar cells (PSCs). However, the existence of multiple low-dimensional phases formed during the film preparation hinders the efficient transport of charge carriers. In addition, the non-homogeneous distribution of low-dimensional phases leads to lattice distortion and increases the defect density, which are undesirable for the stability of tin-based PSCs. Here, mixed spacer cations [diethylamine (DEA⁺) and phenethylamine (PEA⁺)] are introduced into tin perovskite films to modulate the distribution of the 2D phases. It is found that compared to the film with only PEA⁺, the combination of DEA⁺ and PEA⁺ favors the formation of homogeneous low-dimensional perovskite phases with three octahedral monolayers (n = 3), especially near the bottom interface between perovskite and hole transport layer. The homogenization of 2D phases help improve the film quality with reduced lattice distortion and released strain. With these merits, the tin PSC shows significantly improved stability with 94% of its initial efficiency retained after storing in a nitrogen atmosphere for over 4600 h, and over 80% efficiency maintained after continuous illumination for 400 h.

An aromatic imidazole diammonium, 2-(1H-imidazol-2-yl)ethylammonium, is successfully applied as a new spacer for 2D DJ perovskites, which exhibit lower exciton binding energy of 67.8 meV and better carrier transport capability due to the increased dielectric constant. The corresponding device based on (HE)(MA_0.75FA_0.25)₄Pb₅I₁₆ achieves a champion PCE of 18.40% and presents improved environmental stability and operational stability.

Abstract

2D Dion–Jacobson (2D DJ) perovskites are considered as promising photovoltaic materials due to their structural stability and spacer designability. Here, a spacer cation with an aromatic imidazole ring, 2-(1H-imidazol-2-yl)ethylammonium (HE), is successfully applied to construct 2D DJ perovskite. It's found that the high polarity of the HE spacer strengthens the interaction between organic and inorganic layers and reduces the exciton binding energy to 67.8 meV, resulting in promoted charge dissociation, compared with the aliphatic 1,4-butanediammonium (BDA) spacer with a similar length. The HE spacer enlarges the micelle size in precursor solution and suppresses the formation of low-n value phases. In consequence, the HE-based perovskite film exhibits better quality than the BDA-based one, with lower defect density and longer carrier lifetime. The optimized device based on (HE)(MA_0.75FA_0.25)₄Pb₅I₁₆ film achieves a champion power conversion efficiency up to 18.40%, much higher than that of the BDA-based device (15.03%). Besides, the unencapsulated device based HE exhibits improved moisture and thermal stability.

Introducing 2-thiazolemethanammonium (AMT) as a new spacer, the (AMT)MA₃Pb₄I₁₃ device reaches a record PCE of 19.69% for n ≤ 4 2D perovskites. Due to the strong orbital coupling between AMT spacer and inorganic layers, the AMT-based 2D perovskite features a type II quantum well, enhancing exciton separation, and charge transport.

Abstract

2D Dion–Jacobson (DJ) perovskites show structural stability and tunability and are regarded as promising photovoltaic materials. The spacer cations play an important impact on exciton separation and charge transport of 2D perovskites. Herein, a novel spacer with thiazole as core, 2-thiazolemethanammonium (AMT), owning characters of small molecular size, delocalized π-electrons, and strong electron-withdrawing ability, is introduced to construct 2D DJ perovskites. Owing to the strong orbital coupling between AMT spacer and inorganic layers, the AMT-based perovskite exhibits type II quantum well structure, which is favorable for exciton separation. On contrary, such interaction does not appear in the DJ perovskite when aliphatic propyldiammonium (PDA), with a similar length, is used as spacer. The AMT spacer can also induce better crystallinity, resulting in reduced defect density and improved charge transport ability. The optimized device based on (AMT)MA₃Pb₄I₁₃ exhibits a power conversion efficiency (PCE) of 19.69%, which is a record for 2D DJ perovskite solar cells (PSCs) (n ≤ 4). This work provides deep understanding of the impact of aromatic spacer on the electronic structure of 2D DJ perovskites and the corresponding photovoltaic performance and provides a new opportunity toward highly efficient and stable PSCs.

In this study, the potential of the application of cost-effective TiN plasmonic NPs in perovskite solar cells is explored. TiN NPs induce a plasmonic effect, increasing absorption and reducing reflectance. They promote larger perovskite grains, enhancing charge transport and achieving an efficiency of 21.37% as compared to 19.17 of the reference device.

Abstract

Incorporating noble-metal plasmonic nanoparticles (NPs) enhances the optoelectronic properties of perovskite solar cells (PSCs) but at a higher cost. In this work, the overlooked potential of refractory plasmonic materials is highlighted as a cost-effective alternative additive in PSC research. This investigation aims to stimulate interest in this area by showcasing the theoretical and practical impacts of TiN plasmonic NPs when integrated into PSCs. TiN plasmonic NPs present a cost-effective yet underexplored option. This study explores the impact of TiN NPs on PSCs through theoretical and experimental approaches. Finite-difference time-domain (FDTD) optical simulations and empirical data indicate that TiN NPs increase absorption and reduce reflectance in PSCs, driven by surface plasmon resonance and the significant growth of perovskite grains from 450 to 1400 nm. These NPs also regulate the perovskite crystallization rate by adsorbing DMF/DMSO, fostering larger grain formation. Improved band alignment and decreased trap states enhance charge transport and diminish non-radiative recombination losses. As a result, PSC efficiency with optimal TiN NP concentration increased from 19.07% to 21.37%. Additionally, TiN-enhanced PSCs display better stability, retaining 98.1% of their original PCE after 31 days under ambient conditions.