Chen Weijie

A high-performance transparent electron-selective passivating contact for crystalline silicon solar cells is reported. By the implementation of the (intrinsic hydrogenated amorphous silicon) /magnesium oxide/aluminium doped zinc oxide front contact, a high power conversion efficiency of 23.3% is achieved on silicon heterojunction solar cells. This work expands the pool of available metal compound-based passivating contacts for crystalline silicon solar cells.

Abstract

High-efficiency silicon solar cells featuring doped silicon layer-based carrier-selective contacts suffer from optical losses due to parasitic absorption. In this work, a high-performance electron-selective contact with high transparency is presented, consisting of intrinsic hydrogenated amorphous silicon (a-Si:H) passivation layer, atomic-layer-deposited conductive magnesium oxide (MgO_x) and low-work-function aluminium doped zinc oxide (AZO). The a-Si:H/MgO_x/AZO stack is demonstrated to be an excellent and transparent electron-selective contact on c-Si, featuring a small contact resistivity (ρ _c) of 56.0 mΩ cm² and a low saturation current density (J ₀) of 2.9 fA cm⁻² simultaneously. By the implementation of the a-Si:H/MgO_x/AZO front contact, a high power conversion efficiency (PCE) of 23.3% is achieved on silicon heterojunction (SHJ) solar cells, featuring an absolute short-circuit current density (J _sc) and PCE gain of 1.3 mA cm⁻² and 1.2%, respectively, compared to the conventional phosphorus-doped silicon layer-based electron-selective contact. Moreover, a state-of-the-art PCE of 22.8% is obtained on c-Si solar cells with dopant-free asymmetric heterocontacts on both sides, featuring an a-Si:H/MgO_x/AZO front contact and an a-Si:H/vanadium oxide (VO_x) rear contact.

Modulating the redistribution of excess lead iodide in perovskite films by introducing N-Methyl-2-pyrrolidone in the precursor solution, excess lead iodide migrates toward the perovskite film surface during formation, significantly reducing its presence at the buried interface. The blade-coated inverted perovskite solar cells exhibits an efficiency of up to 24.5% and the developed large-area modules achieved 20.3% efficiency.

Abstract

Blade-coating stands out as an alternative for fabricating scalable perovskite solar cells. However, it demands special control of the precursor composition regarding nucleation and crystallization and currently exhibits lower performance than the spin-coating process. It is mainly the resulting film morphology and excess lead iodide (PbI₂) distribution that influences the optoelectronic properties. Here, the effectiveness of introducing N-Methyl-2-pyrrolidone (NMP) to regulate the structure of the perovskite layer and the redistribution of PbI₂ is found. The introduction of NMP leads to the accumulation of excess PbI₂, mainly on the top surface, reducing residual PbI₂ at the perovskite buried interface. This not only facilitates the passivation of perovskite grain boundaries but also eliminates the potential degradation of the PbI₂ triggered by light illumination in the perovskite buried interface. The optimized NMP-modified inverted perovskite solar cell achieves a champion efficiency of 24.5%, among the highest reported blade-coated perovskite solar cells. Furthermore, 13.68 cm² blading perovskite solar modules are fabricated and demonstrate an efficiency of up to 20.4%. These findings underscore that with proper modulation of precursor composition, blade-coating can be a feasible and superior alternative for manufacturing high-quality perovskite films, paving the way for their large-scale applications in photovoltaic technology.

A novel and multifunctional additive-ethacridine lactate is introduced to improve the air-processed CsPbI₃ perovskite film, which simultaneously regulates crystallization, reduces defect and promotes charge transport. Consequently, a high efficiency of 21.08 % was realized, representing the record value for the inverted inorganic perovskite solar cells.

Abstract

All-inorganic cesium lead triiodide perovskites (CsPbI₃) have attracted increasing attention due to their good thermal stability, remarkable optoelectronic properties, and adaptability in tandem solar cells. However, N₂-filled glovebox is generally required to strictly control the humidity during film fabrication due to the moisture-induced black-to-yellow phase transition, which remains a great hinderance for further commercialization. Herein, we report an effective approach via incorporating multifunctional ethacridine lactate (EAL) to mitigate moisture invasion and enable the fabrication of efficient inverted (p-i-n) CsPbI₃ perovskite solar cells (PSCs) under ambient condition. It is revealed that the lactate anions accelerate the crystallization of CsPbI₃, shortening the exposure time to moisture during film fabrication. Meanwhile, the conjugated backbone and multiple functional groups in the ethacridine cations can interact with I⁻ and Pb²⁺ to reduce the undesired defects, stabilize the perovskite structure and facilitate the charge transport in the film. Moreover, EAL incorporation also leads to better energy alignment, thus favoring charge extraction at both upper and bottom interfaces. Consequently, the device efficiency and stability are enormously enhanced, with the champion efficiency reaching 21.08 %. This even surpasses the highest value reported for the devices fabricated in glovebox, representing a record efficiency of inverted all-inorganic PSCs.

Publication date: September 2024

Source: Nano Energy, Volume 128, Part A

Author(s): Zheng Wang, Jiakang Zhang, Sunardi Rahman, Sri Kasi Matta, Mrinal Kanti Si, Zhenhao Zhang, Muhua Zou, Hongzhen Wang, Salvy P. Russo, Zhongmin Zhou, Haichang Zhang, Maning Liu

A facile ambient air-aging process is employed to realize the fabrication of high-quality Cs_0.15FA_0.75MA_0.1PbI₃ perovskite films and thus efficient perovskite solar cells. Comparative studies on the power conversion efficiencies of the devices demonstrate that H₂O molecules in ambient air rather than O₂ molecules induce an effective defect passivation. The positive effect of H₂O on cell performance is irreversible and remains even if moisture escapes.

The quality of perovskite light-harvesting layer is known to be the most critical factor for the performance of perovskite solar cells (PSCs). Herein, a facile ambient air-aging process (AAP, 20%–30% RH) is adopted to realize the fabrication of high-quality Cs_0.15FA_0.75MA_0.1PbI₃ perovskite films, thereby upgrading device performance. We find that the perovskite crystallinity after AAP for 10 d is greatly intensified, with large grain size and preferred crystal orientation along (110) and (220) planes. Comparative studies on the Ag-based devices employing the perovskite films upon exposing to different atmospheres, i.e., dry N₂, dry O₂, N₂, and H₂O (20%–30% RH) and ambient air (20%–30% RH), demonstrate that H₂O molecules in air rather than O₂ molecules induce an effective defect passivation that holds the multiple functions in enhancing the quality of perovskite film, inhibiting the nonradiative recombination, prolonging the carrier lifetime, and improving the energy level matching, etc. Moreover, the positive effect of H₂O in ambient atmosphere on cell performance is irreversible and remains even if moisture escapes. Finally, the average power conversion efficiency (PCE) of device based on the AAP-induced film is increased from 18.24 ± 1.49 to 21.34 ± 0.76, with the champion PCE up to 22.60%. Also, the device with AAP exhibits better moisture resistance capability. Herein, it offers a viable AAP-induced route for the perovskite films with superb optoelectronic properties that can be subsequently extended to the design and construction of other photovoltaic devices for practical application.

Po-SAM strategy is proposed to improve the coverage of SAM and to introduce functional groups, which reduces the current leakage of the devices, improves the wettability, facilitates the perovskite crystallization, and passivates the defects at the buried interface. As a result, the target device achieved a high efficiency of over 25% (certified 24.67%, 0.0817 cm²) with enhanced storage and operation stability.

Abstract

The self-assembled monolayer (SAM) is now widely applied at the hole-selective interface of efficient inverted perovskite solar cells (PSCs). However, voids are unavoidable in SAMs due to the rough substrate and the deposition conditions, which lead to direct contact between the active layer and electrode, undermining the efficiency and stability of PSCs. Here, alkylphosphonic acids with different alkyl chain length are post-assembled to fill the voids, thereby forming a compact po-SAM layer. By further modifying the head group of alkylphosphonic acids, the efficiency and stability of PSCs are improved due to wetting and passivation. Finally, the po-SAM layer formed by (2-Bromoethyl) phosphonic acid and [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid contributes to a champion device with the power conversion efficiency of 25.16% (certified 24.67%) and improved stability under operation or storage. This work demonstrates the advantages of po-SAM layer in improving the performance of PSCs, offering ideas for SAM modification.

Ammonium iodides have excellent chemical passivation effects, but the device stability issues caused by their protonation remain unresolved, hindering the further application of FAPbI₃ perovskite solar cells. Here, the preparation of co-passivating molecules is explored using multifunctional peptides combined with ammonium iodides as interface modifiers to suppress deprotonation of ammonium and passivate surface defects of perovskite. High-performance devices with power conversion efficiencies of over 25% in the 0.05 cm² active area and over 19% in the 18 cm² active area are achieved with excellent light stability.

Abstract

Ammonium iodides are intensively investigated as effective interfacial passivation agents in perovskite solar cells (PSCs) while facing a major challenge of their high reactivity with perovskites that undermines the operational stability of the PSCs. Exemplified by involving rationally designed/selected peptide into the widely adopted phenethylammonium iodide (PEAI), the present work demonstrates that the bespoke peptide-PEAI can effectively inhibit the deprotonation of ammonium iodides and thus hinder the formation of 2D perovskite, facilitating the stability enhancement in perovskite films by multi hydrogen bonding. The additional lone pair electrons provided by peptide molecules can also enhance the passivation ability of the modified layer. Attributed to the stable co-modifier peptide-PEAI, the small-area FAPbI₃-based PSCs yield a high efficiency of 25.02% with robust light and thermal stabilities. Moreover, the peptide-PEAI-based minimodules with an efficiency of 19.06% for a total area of 36 cm² manifested the great application potential of this co-modification strategy in the perovskite photovoltaics.

The efficient and stable inverted perovskite solar cells are developed by introducing ethyl thioglycolate for synergistic crystallization modulation, surface passivation and interfacial PbI₂/I₂ management.

Abstract

As the core component of sandwich-like perovskite solar cells (PSCs), the quality of perovskite layer is a challenge for further progress in PSCs due to the unfavorable defects and uncontrollable crystallization. Here, a surface post-treatment strategy employing ethyl thioglycolate (ET) as ligand molecule is developed for property manipulation of perovskite films. ET can lower surface energy of perovskite facets and induces secondary growth of grains, giving films with higher crystallinity and lower defect density. Meanwhile, both carbonyl and sulfhydryl in ET can bind to the Pb²⁺, thus forming bidentate anchoring on the surface for defect passivation. Besides, the perovskite/ET/C₆₀ interface presents improved charge transfer owing to the well-aligned energy levels. Consequently, the power-conversion-efficiency (PCE) is boosted to 22.42% and 23.56% (certified 23.29%) for the FA_0.85Cs_0.15Pb(I_0.95Br_0.05)₃ and FA_0.9MA_0.05Cs_0.05Pb(I_0.95Br_0.05)₃ PSCs, respectively, and the FA_0.85Cs_0.15Pb(I_0.95Br_0.05)₃-based PSC with a larger area (1.03 cm²) delivers a PCE of 20.01%. Importantly, ET demonstrates effective management of I₂ and PbI₂, thereby preventing accelerated degradation and lead leakage of devices. Thanks to the multiple effects of ET, the resulting devices exhibit significantly enhanced ambient stability over a course of 800 h, and a thermal stability of over 1500 h while maintaining 80.4% of its original efficiency.

Nature Energy, Published online: 12 June 2024; doi:10.1038/s41560-024-01557-z

Photon-recycling (PR) and luminescent coupling (LC) in all-perovskite tandem solar cells are quantified using a Green's tensor model for internal emission and re-absorption coupled to charge transport simulations. This enables the assessment of the upper limit of performance enhancement by PR and LC and of its quenching by optical and and electronic losses such as parasitic absorption and non-radiative recombination.

The impact of photon recycling (PR) and of luminescent coupling (LC) on the photovoltaic performance of all-perovskite tandem solar cells is analyzed by the means of optical and full opto-electronic device simulation. Optical processes are assessed using a comprehensive Green function formalism that considers wave optical effects also in emission. Starting from a consistent fit of experimental sub-cell and tandem characteristics, the effects of re-absorption are propagated from the optical limit to a situation with consideration of realistic charge transport across the entire tandem device. This also provides insight into the origin of performance losses due to sub-cell and interconnection quality.

Potassium 1-trifluoroboratomethylpiperidine (3FPIP) is introduced as the buried interface to improve the charge transfer capability and passivate defects between hole transport layer and perovskite. The champion performance of the device treated by 3FPIP buried interface achieves 24.6%.

Abstract

The properties of an interface at the hole transport layer (HTL)/perovskite layer are crucial for the performance and stability of perovskite solar cells (PVSCs), especially the buried interface between HTL and perovskite layer. Here, a molecular named potassium 1-trifluoroboratomethylpiperidine (3FPIP) assistant-modified perovskite bottom interface strategy is proposed to improve the charge transfer capability and balances energy level between HTL and perovskite. BF₃ ⁻ in the 3FPIP molecule interacts with undercoordinated Pb²⁺ to passivate iodine vacancies and enhance PVSCs performance. Furthermore, the infiltration of K⁺ ions into perovskite molecules enhances the crystallinity and stability of perovskite. Therefore, the PVSCs with the buried interface treatment exhibit a champion performance of 24.6%. More importantly, the corresponding devices represent outstanding ambient stability, remaining at 92% of the initial efficiency after 1200 h. This work provides a new method of buried interface engineering with functional group synergy.

Deposition of fluorinated thiophenethylammonium molecules via the dynamic spray coating result in a passivating dipole layer conformal coatings on fully-textured CZ silicon, which can suppress non-radiative charge recombination and improve interfacial electron extraction. This approach leads to perovskite-silicon tandem solar cells based on industrially fully-textured silicon with a certified efficiency of 30.89 % and excellent stability.

Abstract

Developing large-scale monolithic perovskite/silicon tandem devices based on industrial Czochralski silicon wafers will likely have to adopt double-side textured architecture, given their optical benefits and low manufacturing costs. However, the surface engineering strategies that are widely used in solution-processed perovskites to regulate the interface properties are not directly applicable to micrometric textures. Here, we devise a surface passivation strategy by dynamic spray coating (DSC) fluorinated thiophenethylammonium ligands, combining the advantages of providing conformal coverage and suppressing phase conversion on textured surfaces. From the viewpoint of molecular engineering, theoretical calculation and experimental results demonstrate that introducing trifluoromethyl group provide more effective surface passivation through strong interaction and energy alignment by forming a dipole layer. Consequently, the DSC treatment of this bifunctional molecule enables the tandem cells based on industrial silicon wafers to achieve a certified stabilized power conversion efficiency of 30.89 %. In addition, encapsulated devices display excellent operational stability by retaining over 97 % of their initial performance after 600 h continuous illumination.

Polymer acceptors with BDD units have been developed with large internal space and pronounced steric hindrance, mitigating the entanglements between adjacent polymer chains and increasing the miscibility of polymer donor and polymer acceptor, thus achieving high efficiencies of 17.50 % and 18.64 % in binary and ternary blend all-polymer solar cells.

Abstract

All-polymer solar cells have experienced rapid development in recent years by the emergence of polymerized small molecular acceptors (PSMAs). However, the strong chain entanglements of polymer donors (P_Ds) and polymer acceptors (P_As) decrease the miscibility of the resulting polymer mixtures, making it challenging to optimize the blend morphology. Herein, we designed three P_As, namely PBTPICm-BDD, PBTPICγ-BDD and PBTPICF-BDD, by smartly using a BDD unit as the polymerized unit to copolymerize with different Y-typed non-fullerene small molecular acceptors (NF-SMAs), thus achieving a certain degree of distortion and giving the polymer system enough internal space to reduce the entanglements of the polymer chains. Such effects increase the chances of the P_D being interspersed into the acceptor material, which improve the solubility between the P_D and P_A. The PBTPICγ-BDD and PBTPICF-BDD displayed better miscibility with PBQx-TCl, leading to a well optimized morphology. As a result, high power conversion efficiencies (PCEs) of 17.50 % and 17.17 % were achieved for PBQx-TCl : PBTPICγ-BDD and PBQx-TCl : PBTPICF-BDD devices, respectively. With the addition of PYFT-o as the third component into PBQx-TCl : PBTPICγ-BDD blend to further extend the absorption spectral coverage and finely tune microstructures of the blend morphology, a remarkable PCE of 18.64 % was realized finally.

Publication date: 1 September 2024

Source: Electrochimica Acta, Volume 497

Author(s): Yuhuan Song, Jialong Cong, Wenrui Yu, Haipeng Jiang, Le Zhang, Yingjie Wang, Ming Lu, Fengyou Wang, Lin Fan, Xiaoyan Liu, Maobin Wei, Lili Yang, Nannan Yang

In this work, a dual-functional 1,4-phenylenedimethanammonium (PDMA) molecule is introduced as a new Dion–Jacobson-type spacer and an effective passivation agent for efficient and stable CsPbI₃-based 2D perovskite solar cells. The solar cell device based on the n = 4 film delivers a champion power conversion efficiency of 11.27%, further improved to 12.61% by treating with the PDMA molecules.

Herein, a new type of CsPbI₃-based 2D Dion–Jacobson (DJ) perovskites is reported, featuring a general formula of (PDMA)Cs _n−1PbnI_3n+1 (n = 1, 2, 3, 4) with 1,4-phenylenedimethanammonium (PDMA) as the organic spacer cation. The crystal structure, optical and electric properties, and surface morphology of the perovskite films are fully surveyed. The solar cell device based on the n = 4 film delivers a champion power conversion efficiency (PCE) of 11.27%, further improved to 12.61% by treating with the PDMA molecules. The PDMA passivation suppresses non-radiative recombination, extends charge-carrier lifetime, and reduces open-circuit voltage loss. A gradient energy level near the film surface facilitates electron extraction, alleviating charge accumulation. The PDMA molecules form a protective layer, inhibiting water infiltration and enhancing stability. The optimized device exhibits excellent shelf stability with no PCE decay after 110 days. In this study, a dual-functional molecule is introduced as a new DJ-type spacer and an effective passivation agent for efficient and stable CsPbI₃-based 2D perovskite solar cells.

A mechanical compression strategy, which can not only densify porous carbon electrode for high film conductivity but also provide intimate contact between carbon and perovskite layers for fast charge extraction, is developed for hole transport layer-free and carbon electrode-based perovskite solar cells. The obtained solar cells yield a significant efficiency improvement from 11.98% to 15.29%, together with remarkably enhanced stability.

Carbon electrode-based perovskite solar cells (C-PSCs) without hole transport layer (HTL) have been emerging as a promising low-cost photovoltaic technology with excellent stability for commercialization. However, the loose physical contact between the carbon electrode and perovskite layer, as well as the relatively poor conductivity of the carbon film, contributes mainly to the large gap in the power conversion efficiency (PCE) between C-PSCs and the metal (Ag, Au, etc.,) electrode-based counterparts. To this end, a simple but effective mechanical compression strategy for efficient C-PSCs is developed. The mechanical compression densifies the porous carbon electrode for high film conductivity and also provides intimate contact between carbon and perovskite layers for fast charge extraction. Consequently, the resulting HTL-free C-PSCs using MAPbI₃ (MA = methylammonium) absorber yield a PCE of 15.29%, corresponding to a 27.6% improvement compared to the counterpart without mechanical pressing treatment. Moreover, the compacted carbon film also serves as an enhanced barrier against the intrusion of water and oxygen, and the unencapsulated device retains 88.9% of its initial PCE after 1000 h of aging in ambient conditions with 35 ± 2% humidity. This work paves a simple and effective way toward efficient and stable C-PSC.

A novel method, ethanol solvent-assisted chemical deposition (S-CBD), is developed to control the film's growth rate higher than its nucleation rate, thereby enhancing the grain size and electrical properties of the Sb₂S₃ film and boosting device performance through this self-regulation of the precursor solution.

Abstract

Antimony sulfide (Sb₂S₃) has attracted extensive attention due to its excellent photoelectric characteristics, including a high absorption coefficient (α > 10⁴ cm⁻¹) and a suitable bandgap (≈1.7 eV). However, due to its Q1D (quasi-1D) structure, numerous deep-level defects are identified in the Sb₂S₃ film, limiting the device's performance, and necessitating more efforts to overcome this situation. In this context, an ethanol solvent-assisted chemical bath deposition (S-CBD) strategy, a novel high-quality thin film manufacturing technique is presented that modifies the supersaturation of the precursor solution by varying the boiling point and solvent polarity. This approach enables the effective regulation of the correlation between the crystal nucleation and growth rates, resulting in Sb₂S₃ films with large grains (≈4.25 µm, 37.5% ethanol), excellent crystallinity, well-oriented structures (TC₍₂₁₁₎/TC₍₀₂₀₎ = 2.39), low defect density, and prolonged carrier lifetimes (τ_Ave ≈ 12.1 ns). Consequently, the final Sb₂S₃-based solar device (FTO/CdS/Sb₂S₃/Spiro-OMeTAD/Au) shows significant improvements in both FF (61.63%) and J _SC (17.61 mA cm⁻²), yielding an excellent power conversion efficiency (PCE) of 7.84%. This research gives particular insights into the growth mechanism of high-quality Sb₂S₃ thin films by CBD method as well as a potential route for enhancing Sb₂S₃ solar cell performance.

Enhancing the performance of printable mesoscopic perovskite solar cells (p-MPSCs) hinges on effective defect rectification. In this innovative study, a synergistic ‘two-in-one’ defect passivation method involving enriching the TiO₂ electron transport layer with a series of cesium halide salts, especially CsF is presented. This integration plays a pivotal role in addressing two critical types of defects: F^─ effectively mends oxygen vacancies within the TiO₂, mitigating interface stress, while Cs⁺ targets and repairs methylamine vacancies within the perovskite structure. Consequently, a remarkable increase in power conversion efficiency is obtained, soaring from 16.18% to 18.24%, thereby significantly elevating the efficacy of p-MPSCs.

Abstract

In the rapidly advancing realm of perovskite solar cells, the rectification of defects has surfaced as a crucial scientific challenge. The control over defect states, especially in printable mesoscopic perovskite solar cells (p-MPSCs), is hindered by the complexities of screen-printing technology. Here a novel “two-in-one” defect passivation strategy is presented, through doping TiO₂ paste with cesium halide salts (CsX, where X = F, Cl, Br, I) to integrate all-inorganic Cs halides, particularly CsF, into the electron transport layer in p-MPSCs. Owing to the robust interaction between F⁻ ions and TiO₂ compared to Cs⁺ ions, and the inability of F⁻ to infiltrate the perovskite lattice, F⁻ and Cs⁺ play distinct roles starting from the buried interface of the p-MPSCs. Specifically, F⁻ can rectify the oxygen vacancies on the TiO₂ surface, thus alleviating the residual stress at the perovskite's buried interface. Simultaneously, Cs⁺ diffuses to the top perovskite and mends the methylamine vacancies. As a result, the PCE of the optimal device, based on F-doped TiO₂, witnesses a significant improvement from 16.18% (control) to 18.24%. The two-in-one strategy utilizing CsX from the buried interface can well realize the all-inorganic defect rectification, thereby offering a promising prospect for the enhancement of p-MPSC performance.

A method of stabilizing perovskite ink is proposed. This method uses benzylhydrazine hydrochloride (BHC) to stabilize the organic cations of perovskite ink, and remove harmful water impurities, while also reducing iodine back to iodide as has already been discovered. The downstream products of BHC and iodine are investigated via 1D and 2D NMR spectroscopy and found to be chemically benign. All scalable perovskite solar cells are made with BHC ink and found to have nearly 20 % efficiency.

Abstract

Perovskite precursor inks suffer various forms of degradation, such as iodide anion oxidation and organic cation breakdown, hindering reliable perovskite solar cell manufacturing. Here we report that benzylhydrazine hydrochloride (BHC) not only retards the buildup of iodine as previously reported but also prevents the breakdown of organic cations. Through investigating BHC and iodine chemical reactions, we elucidate protonation and dehydration mechanisms, converting BHC to harmless volatile compounds, thus preserving perovskite film crystallization and solar cell performance. This inhibition effect lasts nearly a month with minimal BHC, contrasting control inks without BHC where organic cations fully react in less than a week. This enhanced understanding, from additive stabilization to end products, promises improved perovskite solar cell production reliability.

Publication date: October 2024

Source: Journal of Energy Chemistry, Volume 97

Author(s): Yu Liu, Kun Lang, Huifang Han, Huijing Liu, Yao Fu, Pengchen Zou, Yinhui Lyu, Jia Xu, Jianxi Yao

Publication date: 1 September 2024

Source: Electrochimica Acta, Volume 497

Author(s): Zhenwu Zhong, Xiaoyu Yang, Zhaoxiang Qi, Ke Zhao, Salman Riaz, Ying Qi, Peng Wei, Min Jae Ko, Jian Cheng, Yahong Xie

This work systematically demonstrates that the surface dipole formation leads to better charge extraction and surface passivation. Herein, a long-chain alkyl molecule (n-hexyl trimethylammonium bromide) is used at the CsPbI₃ and poly(3-hexylthiophene) interface that acts as a dipole, mitigating traps and enhancing charge extraction. The study is supported by photoluminescence emission spectroscopy, the Kelvin probe method, and time-resolved surface photovoltage measurements.

The efficient functioning of perovskite solar cells largely depends on the interaction between perovskite halide materials and the hole-transport layer poly(3-hexylthiophene) (P3HT). However, a high rate of nonradiative recombination often hampers this interaction, leading to poor performance of the solar cells. We have developed a technique to modify the interface using a long-chain alkyl halide molecule called n-hexyl trimethylammonium bromide to address this issue. This modification technique significantly improves hole extraction, leading to an impressive open-circuit voltage of 1.14 V and a power conversion efficiency of 15.8% for inorganic perovskite CsPbI₃ with P3HT as a dopant-free hole-transport layer. This breakthrough can pave the way for developing more efficient and sustainable solar cells.

The introduction of 1H-Pyrazole-1-carboximidamide hydrochloride (PCH) into FAPbI₃ perovskite films significantly improves crystallinity, reduces defect density, and enhances V _oc and Fill Factor, achieving a record power conversion efficiency of 24.62% with exceptional stability, highlighting PCH's efficacy as an additive for high-performance perovskite solar cells.

Abstract

Perovskite materials, particularly FAPbI₃, have emerged as promising candidates for solar energy conversion applications. However, these materials are plagued by well-known defects and suboptimal film quality. Enhancing crystallinity and minimizing defect density are therefore essential steps in the development of high-performance perovskite solar cells. In this study, 1H-Pyrazole-1-carboximidamide hydrochloride (PCH) is introduced into FAPbI₃ perovskite films. The molecular structure of PCH features a pyrazole ring bonded to formamidine (FA). The FA moiety of PCH facilitated the incorporation of this additive into the film lattice, while the negatively charged pyrazole ring effectively passivated positively charged iodine vacancies. The presence of PCH led to the fabrication of an FAPbI₃ device with improved crystallinity, a smoother surface, and reduced defect density, resulting in enhanced V _oc and fill factor. A record power conversion efficiency of 24.62% is achieved, along with exceptional stability under prolonged air exposure and thermal stress. The findings highlight the efficacy of PCH as a novel additive for the development of high-performance perovskite solar cells.

Incorporating Ag in kesterite materials is crucial for surpassing 13% efficiencies. However, it reduces the density of CuZn defects, resulting in a suboptimal majority carrier density near 1015 cm⁻³. This work provides a simple approach to tune the majority carrier density to optimal values over 10¹⁶ cm⁻³, leading to record-level efficiencies above 14% and enabling efficiencies close to 20%.

Abstract

Kesterite photovoltaic technologies are critical for the deployment of light-harvesting devices in buildings and products, enabling energy sustainable buildings, and households. The recent improvements in kesterite power conversion efficiencies have focused on improving solution-based precursors by improving the material phase purity, grain quality, and grain boundaries with many extrinsic doping and alloying agents (Ag, Cd, Ge…). The reported progress for solution-based precursors has been achieved due to a grain growth in more electronically intrinsic conditions. However, the kesterite device performance is dependent on the majority carrier density and sub-optimal carrier concentrations of 10¹⁴–10¹⁵ cm⁻³ have been consistently reported. Increasing the majority carrier density by one order of magnitude would increase the efficiency ceiling of kesterite solar cells, making the 20% target much more realistic. In this work, LiClO₄ is introduced as a highly soluble and highly thermally stable Li precursor salt which leads to optimal (>10¹⁶ cm⁻³) carrier concentration without a significant impact in other relevant optoelectronic properties. The findings presented in this work demonstrate that the interplay between Li-doping and Ag-alloying enables a reproducible and statistically significant improvement in the device performance leading to efficiencies up to 14.1%.

Publication date: September 2024

Source: Nano Energy, Volume 128, Part A

Author(s): Jinpei Wang, Xue Zheng, Chen Zhang, Changshun Chen, Qing Yao, Tingting Niu, Lingfeng Chao, Qingxun Guo, Hui Zhang, Yingdong Xia, Mingjie Li, Hong Lu, Hainam Do, Zhuoying Chen, Guichuan Xing, Zhelu Hu, Yonghua Chen