JIALINGBO

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

Abstract

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

Publication date: 15 December 2023

Source: Nano Energy, Volume 118, Part A

Author(s): Jingxu Tian, Jihuai Wu, Ruoshui Li, Yuhe Lin, Jialian Geng, Wenhui Lin, Ying Wang, Qiang Ouyang, Zhaohui Wu, Weihai Sun, Liqing Li, Zhang Lan, Yu Lin

Publication date: 1 December 2023

Source: Nano Energy, Volume 117

Author(s): Hui Chen, Jiabao Yang, Qi Cao, Tong Wang, Xingyu Pu, Xilai He, Xingyuan Chen, Xuanhua Li

By introducing ammonium sulfamate between the TiO₂ layer and the perovskite layer as an interface modification material, the energy level distribution of TiO₂ is regulated, the interface defects are passivated, the electrical properties of TiO₂ are improved, and the electron transport ability of TiO₂ layer is promoted. Finally, high-efficiency and stable PSCs are prepared.

Abstract

Defects in perovskite films are still the dominant destroyer of both power conversion efficiency (PCE) and long-term stability in perovskite solar cells (PSCs). As the most popular electron transport layer (ETL), TiO₂ film is used in many PSCs to achieve high PCE. However, pristine TiO₂ by itself is not sufficient as an ETL due to lattice mismatch, poor alignment of the energy level gap, and hysteresis of the PSC. Herein, ammonium sulfamate (AS), with desired NH₄ ⁺ and S═O functional groups, is designed to modify the TiO₂ surface and interface to improve the PCE of PSCs. It is found that the AS works like a seed layer for the perovskite deposition, and, in addition, it effectively forms a bridge between the TiO₂ surface and the perovskite. As a result, PSCs are successfully fabricated with a champion power conversion efficiency of 24.78% with smaller hysteresis. The PSCs prepared using the AS-modified TiO₂ also show excellent stability, and the bare device without any encapsulation retains 96% of its initial PCE after 1056 h of ambient exposure at 25 °C and 25% relative humidity.

A solution is sought for the buried interface issues within CsPbI₂Br-based perovskite solar cells. Addressing this, a multifunctional electron transporting layer (ETL) using a PbCl₂-modified ZnO nanocomposite is introduced. By tuning bandgap and energy levels, the ETL enhances energy alignment with CsPbI₂Br. Integration of residual PbCl₂ at the buried interface minimizes defects, ameliorating film quality.

Abstract

CsPbI₂Br perovskite solar cells (PSCs) have garnered significant attention owing to their remarkable thermal stability and desirable bandgap. However, CsPbI₂Br-based devices still face critical challenges, particularly at the interfaces between the active layer and adjacent components. In this study, a multifunctional ZnO composition has developed as the electron transporting layer (ETL) for CsPbI₂Br PSCs, enabling simultaneous efficient charge extraction and passivation of buried interface defects in CsPbI₂Br. The nanocomposite, composed of PbCl₂-modified ZnO (PbCl₂-ZnO), facilitates the regulation of bandgap and conduction band to align the energy level of ETL and CsPbI₂Br. Additionally, the residual PbCl₂ at the buried interface of the perovskite incorporates into the perovskite lattice, reducing I defect and thus improving film quality. The improved energy level alignment at the ETL/CsPbI₂Br interface and the suppressed I defect-induced carrier nonradiative recombination result in a remarkable reduction in energy loss from 0.73 to 0.52 eV. Finally, the PbCl₂-ZnO hybrid nanocomposite ETL significantly enhances the efficiency of CsPbI₂Br PSCs, increasing it from 14.15% to 17.46%, representing one of the highest reported power conversion efficiency (PCE) values for CsPbI₂Br PSCs. These findings demonstrate the potential of PbCl₂-ZnO hybrid nanocomposite as an effective ETL for CsPbI₂Br PSCs.

Herein, the efficient formamidinium-cesium -based inverted perovskite solar cells are developed by introducing 1-(3-aminopropyl)-imidazole (API) for perovskite bottom interface modulation. The appearance of API not only optimizes the energy band between the PTAA/PVK, but also reduces the perovskite bottom defects. Notably, the formation of hydrogen bonds between R-NH₂ of API and I^- strengthens the binding ability of R-C═N and Pb²⁺ defects.

Abstract

Considering the direct influence of substrate surface nature on perovskite (PVK) film growth, buried interfacial engineering is crucial to obtain ideal perovskite solar cells (PSCs). Herein, 1-(3-aminopropyl)-imidazole (API) is introduced at polytriarylamine (PTAA)/PVK interface to modulate the bottom property of PVK. First, the introduction of API improves the growth of PVK grains and reduces the Pb²⁺ defects and residual PbI₂ present at the bottom of the film, contributing to the acquisition of high-quality PVK film. Besides, the presence of API can optimize the energy structure between PVK and PTAA, which facilitates the interfacial charge transfer. Density functional theory (DFT) reveals that the electron donor unit (R-C ═ N) of the API prefers to bind with Pb²⁺ traps at the PVK interface, while the formation of hydrogen bonds between the R-NH₂ of API and I⁻ strengthens the above binding ability. Consequently, the optimum API-treated inverted formamidinium-cesium (FA/Cs) PSCs yields a champion power conversion efficiency (PCE) of 22.02% and exhibited favorable stability.

Introducing the n-type polymer N2200 in PCBM, not only up-shifts the LUMO energy level and enhances the electrical properties of PCBM, but also effectively passivates surface defects on the perovskite layer. PCBM@N2200 devices demonstrate, a V _OC of 1.20 V, leading to an impressive PCE of 24.53% and the corresponding module achieves an efficiency of 20.30% with an active area of 11.19 cm².

Abstract

Phenyl-C61-butyric acid methyl ester (PCBM) remains the most commonly used electron transport layer in inverted perovskite solar cells (IPSCs). However, its insufficient electrical properties and passivation ability limit the device's performance. In this study, it is demonstrated that introducing an appropriate amount of n-type polymer N2200 into the PCBM can simultaneously enhance the electrical properties of PCBM and passivate the defects distributed on perovskite surface. This modification of PCBM leads to improved band alignment and enhanced electron mobility. Simultaneously, N2200 polymer contains electron donors such as O, S involved in passivating uncoordinated Pb²⁺ defects. The PCBM@N2200-based IPSCs exhibit an enhanced open-circuit voltage (V _OC) of 1.20 V with the minimum 0.36 V voltage loss and reach the champion power conversion efficiency (PCE) of 24.53% (certified PCE is 24.05%) with narrow distribution. Impressively, the corresponding module achieves an efficiency of 20.30% (11.19 cm²). Moreover, the PCBM@N2200-based IPSCs maintain 96% of their initial efficiency after operating at the maximum power point for 500 h, thanks to the interfacial passivation, improved uniformity, and increased hydrophobicity resulting from N2200 doping.

The enhanced interaction between 4′-cyanogroup-[1,1′-biphenyl]−4-acyl acrylate and PbI₂ during annealing leads to the formation of a new intermediate complex, which not only induces diffusion-controlled growth but also increases diffusion activation energy, leading to delayed crystallization. Therefore, the optimized device has high efficiency (24.53%) and excellent stability (maintaining 89% of the initial efficiency after 6600 h aging in ambient).

Abstract

Solution crystallization in film devices has attracted broad interest from various fields such as perovskite solar cells. However, the detailed perovskite crystallization kinetics remain unclear due to the difficulty of in situ observation of grain cluster growth during annealing. This article presents the development of an in situ laser scanning confocal polarized microscopy with a temperature-controlled stage to observe nucleation and growth of perovskite crystal clusters. It is found that enhanced interactions by a liquid crystal with perovskite form a new intermediate complex that induces diffusion-controlled growth according to Avrami equation. The retarded cluster growth (63 nm s⁻¹) originates from enlarged diffusion activation energy 40 kJ mol⁻¹ compared with 152 nm s⁻¹ and 37 kJ mol⁻¹ for the Control film during annealing. Finally, the optimized perovskite films with enhanced crystallographic and optical characteristics are applied in solar cells to achieve a champion efficiency of 24.53% with open circuit voltage of 1.172 V and fill factor of 82.78%. The bare device without any protection maintains 89% of its initial efficiency after 6600 h of aging in ambient environment. This work implies that the in situ observation using fluorescence microscopy is a critical for understanding of crystallization kinetics in film devices.

Double-side passivation with phenyltrimethylammonium iodide (PTMAI) improves the performance and stability of PSCs. PTMAI influences the perovskite nanostructures, effectively reducing various defective states. As a result, solar cells with double-side passivation achieve a high power conversion efficiency of 21.87%, withstanding temperatures as high as 60 °C and continuous exposure to 1 sun for over 1800 and 1000 h, respectively.

Abstract

Perovskite solar cells (PSCs) are in the spotlight as promising renewable energy devices by their appealing properties. However, they face challenges both in power conversion efficiency (PCE) and long-term stability. The presence of surface defects in the PSCs is a significant obstacle to achieving both high efficiency and stability, as these defects cause nonradiative recombination and degradation. Herein, a novel double-side surface passivation method using phenyltrimethylammonium iodide (PTMAI) salt is applied to remove electronic defects effectively. Furthermore, double-side passivation with PTMAI contributes to the enhancement of the perovskite crystallinity with the relaxed non-uniform distribution of local strains. Finally, the efficiency of PSC is significantly improved by double-side passivation with PTMAI, achieving a PCE of 21.87%. Furthermore, the passivated cell exhibited enhanced long-term stability, maintaining over 80% of initial PCE after 1860 and 1030 h under 60 °C and 1 sun illumination, respectively.

Obtaining a uniform perovskite layer on Me-4PACz self-assembled monolayer (SAM) presents significant challenges. This is because of poor perovskite ink interaction with the Me-4PACz SAM. Herein, a perovskite ink–substrate interaction strategy is employed using a triple co-solvent system. As a result, a uniform perovskite layer is obtained with improved and reproducible device performance.

Abstract

Perovskite solar cells employing [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer as the hole transport layer have been reported to demonstrate a high device efficiency. However, the poor perovskite wetting on Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink - Me-4PACz coated substrate interaction and obtain a uniform perovskite layer. In comparison to DMF- and DMSO-based inks, the inclusion of NMP shows considerably higher binding energies of the perovskite ink with Me-4PACz as revealed by density-functional theory calculations. With the optimized triple co-solvent ratio, the perovskite devices deliver high power conversion efficiencies of >20%, 19.5%, and ≈18.5% for active areas of 0.16, 0.72, and 1.08 cm², respectively. Importantly, this perovskite ink–substrate interaction approach is universal and helps in obtaining a uniform layer and high photovoltaic device performance for other perovskite compositions such as MAPbI₃, FA_{1− x} MA _x PbI_{3– y} Br _y , and MA-free FA_{1− x} Cs _x PbI_{3– y} Br _y .

We experimentally demonstrate that monolithic perovskite/silicon tandem solar cells possess a superior reverse-bias resilience compared with perovskite single-junction solar cells. The majority of the reverse-bias voltage is dropped across the more robust silicon subcell, protecting the perovskite subcell from reverse-bias-induced degradation. These results highlight the advantages of monolithic perovskite/silicon tandems in withstanding partial shading-induced reverse-bias stress and indicate a higher commercial readiness level of the tandems compared with their perovskite single-junction counterparts.

Tryptamine as an additive is introduced in the hole transport layer. The molecular interactions of tryptamine with perovskite and lithium cation result in a drastic improvement of V _OC from 1.192 to 1.251 V, yielding a high device power conversion efficiency of 21.8%, together with greatly enhanced moisture stability.

Abstract

Metal halide inorganic perovskite solar cells (PSCs) have great potential to achieve high efficiency with excellent thermal stability. However, the surface defect traps restrain the achievement of high open circuit voltage (V _OC) and power conversion efficiency (PCE) of the devices due to the severe nonradiative charge recombination. Moreover, the state-of-the-art hole transporting layer (HTL) significantly hampers device moisture stability, even though it renders the highest solar cell efficiency. Herein, a one-stone-two-birds strategy is proposed using a biocompatible material tryptamine (TA) as an additive in HTL. First, TA bearing electron rich moieties can favorably passivate the surface defects of inorganic perovskite films, significantly reducing trap density and prolonging charge lifetime. It results in a drastic improvement of V _OC from 1.192 to 1.251 V, with a V _OC loss of 0.48 V. The corresponding PSCs achieve a 21.8% PCE under 100 mW cm⁻² illumination. Second, TA in HTL can coordinate with lithium cations, retarding their reaction with moisture and increasing the moisture stability of HTL. Consequently, the black phase of inorganic perovskite films is well preserved, and the corresponding PSCs maintain 90% of the initial PCE after 800 h storage at relative humidity of 25–35%, much higher than the control devices.

This review summarizes the origin of perovskite solar cell (PSC) degradation and the recent development of in situ cross-linking strategy in PSCs to enhance the moisture, thermal, illumination, and tensile stress resistance properties of perovskite. Moreover, the current challenges to further develop the in situ cross-linking strategy to enable high stability and efficiency of PSCs are thoroughly discussed.

Abstract

The perovskite solar cells (PSCs) have achieved great success in power conversion efficiency due to their excellent optoelectrical properties of perovskite. However, the instability of PSCs severely impedes their commercialization. Recently, in situ cross-linking strategy has been proposed to mitigate stability issues of PSCs, enabling highly efficient and stable PSCs. Here, the critical factors that lead to the degradation of PSCs are first outlined. Then, a comprehensive review of in situ cross-linking strategy in perovskite to enhance the moisture, thermal, illumination, and bending stress resistance properties of PSCs is presented. Furthermore, the detailed mechanism underlying these advantageous effects is discussed pertaining to crystallization regulation, immobilization of ions, water resistance, and release of unfavorable stress. Finally, the current challenges and further development trends of in situ cross-linking strategy in PSCs and extension to other optoelectronic devices are prospected.

Ionic liquids can do more! A facile and efficient self-assembled [HOEtMIM]Cl layer is introduced for the first time in the rigid and flexible electron transport layer-free perovskite solar cells, giving rise an improved power conversion efficiency of 19.60 % and 15.57 %, along with an improved hysteresis and stability.

Abstract

The advancement of electron transport layer (ETL)-free perovskite solar cells (PSCs) is crucial for the commercialization of PSCs. At present, the slow electron extraction and significant carrier recombination, related to the energy-level alignment at the FTO/perovskite interface, restrict the performance of ETL-free PSCs. The facile modification of bottom electrodes is pivotal for tackling these issues and stimulating the photovoltaic potential of perovskite. Herein, a cost-competitive and neoteric 1-hydroxyethyl-3-methylimidazolium chloride, [HOEtMIM]Cl, ionic liquid is employed to modify the surface of rigid and flexible electrodes, and thus enable an energetically well-aligned interface with perovskite layer via the electric dipole effects. The resulting barrier-free FTO/perovskite contact can tremendously ameliorate the electron extraction and collection, with mitigated nonradiative interfacial carrier recombination loss. Additionally, the lone pair on the nitrogen of the imidazole group passivates the surface defects of perovskite layers, and the chloride anion plays a role in the crystallinity improvement of perovskite. Leveraged by the [HOEtMIM]Cl modification, the resulting ETL-free rigid and flexible devices deliver an outstanding power conversion efficiency of 19.60 % and 15.57 %, along with the ameliorated hysteresis and long-term tenability. This finding highlights the drastic potential of the engineered [HOEtMIM]Cl in manufacturing stable and high-performance ETL-free PSCs for their scaled-up production.

Directly adding a cyanoacrylic-acid-based molecular additive, namely BT-T, into the perovskite precursor solution achieves in situ buried-interface passivation. The power-conversion efficiency (PCE) for 1.0 cm² inverted-structure PSCs reaches 23.48%. The encapsulated perovskite solar cell (PSC) retains 95.4% of its initial PCE following 1960 h maximum-power-point tracking under continuous light illumination at 65 °C (i.e., ISOS-L-2I protocol).

Abstract

High-performance perovskite solar cells (PSCs) typically require interfacial passivation, yet this is challenging for the buried interface, owing to the dissolution of passivation agents during the deposition of perovskites. Here, this limitation is overcome with in situ buried-interface passivation—achieved via directly adding a cyanoacrylic-acid-based molecular additive, namely BT-T, into the perovskite precursor solution. Classical and ab initio molecular dynamics simulations reveal that BT-T spontaneously may self-assemble at the buried interface during the formation of the perovskite layer on a nickel oxide hole-transporting layer. The preferential buried-interface passivation results in facilitated hole transfer and suppressed charge recombination. In addition, residual BT-T molecules in the perovskite layer enhance its stability and homogeneity. A power-conversion efficiency (PCE) of 23.48% for 1.0 cm² inverted-structure PSCs is reported. The encapsulated PSC retains 95.4% of its initial PCE following 1960 h maximum-power-point tracking under continuous light illumination at 65 °C (i.e., ISOS-L-2I protocol). The demonstration of operating-stable PSCs under accelerated ageing conditions represents a step closer to the commercialization of this emerging technology.

An effective strategy is proposed for managing defects at the perovskite interface, that is, using mixed-salt trimethylsulfoxonium iodide (TMSI) to improve the defect formation energy, fill the iodide vacancies, and inhibit the generation of Pb⁰ defects.

Abstract

Iodine vacancies and uncoordinated Pb⁰ defects existing at the perovskite surface have been widely demonstrated to induce deep-level defects, which can greatly limit improvement of the efficiency and stability of perovskite solar cells (PSCs). In this work, a novel strategy is proposed for functionalizing perovskite surface by using trimethylsulfoxonium iodide (TMSI), which can enhance the defect formation energy and inhibit Pb⁰ defects. Meanwhile, TMSI modification also can fill the iodine vacancies of perovskite surface-terminating ends. Consequently, the optimized device shows the improved charge dynamics and the reduced energy losses, achieving a champion efficiency of up to 24.03% along with excellent air-storage and thermal stabilities. This work offers guidelines for more efficient and stable PSCs based on the management of interface defects.

2-Methylbenzimidazole (MBI) molecular ferroelectric with low coercive field and high Curie-temperature is introduced to construct an additional ferroelectric field in FASnI₃-based perovskite solar cells (PSCs), where the directional polarization of MBI can upgrade the built-in electric field and improve carrier dynamics to enhance the photovoltaic performance of PSCs.

Abstract

Due to the relatively inferior dielectric constant, Sn-based perovskites exhibit lower defect tolerance and insufficient dielectric shielding effect compared with Pb-perovskites. Upgrading built-in electric field (BEF) in Sn-based perovskite solar cells (PSCs) can be effective to reduce large voltage deficit and improve poor performance caused by the low defect tolerance resulting from the intrinsic inferior dielectric of Sn-based perovskites. Herein, 2-methylbenzimidazole (MBI) molecular ferroelectric with low coercive field and high Curie-temperature is introduced to construct an additional ferroelectric field in FASnI₃-based PSCs. The ferroelectric effect of MBI can promote exciton dissociation, enhance carrier population, and suppress the adverse effect of the residual defects on carriers, and the directional polarization of MBI in FASnI₃ film can be driven by the BEF in PSCs to broaden the width of depletion region. Additionally, the MBI molecules with amine functional groups effectively regulate perovskite crystallization, passivate Sn-related defects, and enhance the oxidation barrier. Profiting from the above advantages, the MBI-modified device achieves a champion power conversion efficiency (PCE) of 12.91%, keeping over 94% average PCE after 1056 h in N₂ glovebox for the unencapsulated device. This study highlights the significant role of molecular ferroelectrics in perovskite photovoltaics.

A non-halide ionic salt 1-naphthylmethylammonium formate (NMACOOH) is synthesized for the surface passivation of perovskites. Owing to the strong coordination between HCOO⁻ and Pb²⁺, the formation of 2D perovskite is inhibited, and a thermally stable PbI₂-NMACOOH adduct is formed on the perovskite surface. The passivated devices deliver a champion efficiency of 24.75% with a high open-circuit voltage of 1.19 V.

Abstract

The non-radiative recombination at the interfaces of perovskite solar cells (PSCs) is a crucial issue that limits the efficiency and stability of the devices. State-of-the-art surface passivation strategies usually utilize alkyl ammonium halides to suppress the non-radiative recombination of PSCs, but their high surface reactivity leads to the transformation into 2D perovskites under working conditions, limiting the passivation effect and the charge transport of PSCs. Herein, a non-halide ionic salt 1-naphthylmethylammonium formate (NMACOOH) is synthesized for surface passivation of perovskite films. In contrast to the traditional 1-naphthylmethylammonium iodide, NMACOOH treatment hinders the formation of 2D perovskite and forms a thermally stable PbI₂-NMACOOH adduct on the perovskite surface. Surface characterization reveals that NMA⁺ can passivate the cation vacancies of the 3D perovskite while HCOO⁻ passivates the metallic Pb⁰ and halide-vacancy defects. Therefore, the non-radiative recombination of PSCs is dramatically suppressed and a high open-circuit voltage of 1.19 V is obtained. Finally, PSCs with high efficiency of 24.75% and improved long-term stability (98% of the initial efficiency after 1800-h storage) are obtained. Moreover, the NMACOOH-passivated devices also show robust operational stability, retaining 83% of the initial efficiency after working for 658 h under continuous one-sun illumination.

The α-phase formamidinium lead triiodide perovskite single crystal redissolution strategy facilitates direct α-phase formation with inhibition of complex intermediate phases due to the larger-sized colloidal clusters present in the precursor solution. The resultant film demonstrates significantly improved crystallization and mitigated defects. This strategy relaxes the lattice strain through isotropic orientation phase growth, contributing to the prolonged α-phase stability.

Abstract

Perovskite single-crystal redissolution (PSCR) strategy is highly desired for efficient formamidinium lead triiodide (FAPbI₃) perovskite photovoltaics with enhanced phase purity, improved film quality, low trap-state density, and good stability. However, the phase transition and crystallization dynamics of FAPbI₃ remain unclear in the PSCR process compared to the conventional fabrication from the mixing of precursor materials. In this work, a green-solvent-assisted (GSA) method is employed to synthesize centimeter-sized α-FAPbI₃ single crystals, which serve as the high-purity precursor to fabricate perovskite films. The α-FAPbI₃ PSCR strategy facilitates direct α-phase formation and inhibits the complex intermediate phases monitored by in situ grazing-incidence wide-angle X-ray scattering. Moreover, the α-phase stability is prolonged due to the relaxation of the residual lattice strain through the isotropic orientation phase growth. Consequently, the GSA-assisted PSCR strategy effectively promotes crystallization and suppresses non-radiative recombination in perovskite solar cells, which boosts the device efficiency from 22.08% to 23.92% with significantly enhanced open circuit voltage. These findings provide deeper insight into the PSCR process in terms of its efficacy in phase formation and lattice strain release. The green low-cost solvent may also offer a new and ideal solvent candidate for large-scale production of perovskite photovoltaics.

Publication date: November 2023

Source: Nano Energy, Volume 116

Author(s): Chao Gao, Haotian Zhang, Feiyang Qiao, Huanpei Huang, Dezhao Zhang, Dong Ding, Daxue Du, Jingjing Liang, Jiahao Bao, Hong Liu, Wenzhong Shen

In this work, a self-assembled bilayer comprising a covalent monolayer (Br-2PACz) and a wetting layer (4CzNH₃I) as HTL in a Sn/Pb perovskite solar cell is implemented. It is demonstrated that the 4CzNH₃I layer completely solves the wettability problem due to the higher polarity of the newly formed surface. The NH₃ ⁺ groups also help in the passivation of the buried interface.

Abstract

Recently, carbazole-based self-assembled monolayers (SAMs) have been utilized as hole transport layers (HTLs) in perovskite solar cells. However, their application in Sn or mixed Sn/Pb perovskite solar cells has been hindered by the poor wettability of the perovskite precursor solution on the carbazole surface. Here a self-assembled bilayer (SAB) comprising a covalent monolayer (Br-2PACz) and a noncovalent wetting layer (4CzNH₃I) as the HTL in a Cs_0.25FA_0.75Sn_0.5Pb_0.5I₃ perovskite solar cell is proposed. It is demonstrated that the wetting layer completely solves the problem due to the higher polarity of the surface and, furthermore, the ammonium groups help in the passivation of trap states at the buried SAB/perovskite interface. The introduction of the SAB enhances the device reproducibility with an average efficiency of 18.98 ± 0.28% (19.45% for the best device), compared to 11.54 ± 9.36% (19.34% for the best device) for the SAM-only devices. Furthermore, the improved perovskite processability on the SAB helps to increase the reproducibility of larger size device, where, a 12.5% efficiency for a 0.8 cm² active area device compared to 0.68% for the best SAM-based solar cell is demonstrated. Finally, the device's operational stability is also improved to 358 hours (T_80%), compared to 220 hours for the SAM-based solar cell.

Operando photoluminescence measurements and drift-diffusion simulations are used to investigate the performance of perovskite solar cells with different electron transport materials (ETMs). It is demonstrated that the energetic alignment at the perovskite/ETM interface strongly influences the balance between electronic charge extraction and recombination. Moreover, electronic charge accumulation is observed at short-circuit, which is attributed to field screening by mobile ions.

Abstract

Understanding the kinetic competition between charge extraction and recombination, and how this is impacted by mobile ions, remains a key challenge in perovskite solar cells (PSCs). Here, this issue is addressed by combining operando photoluminescence (PL) measurements, which allow the measurement of real-time PL spectra during current–voltage (J–V) scans under 1-sun equivalent illumination, with the results of drift-diffusion simulations. This operando PL analysis allows direct comparison between the internal performance (recombination currents and quasi-Fermi-level-splitting (QFLS)) and the external performance (J–V) of a PSC during operation. Analyses of four PSCs with different electron transport materials (ETMs) quantify how a deeper ETM LUMO induces greater interfacial recombination, while a shallower LUMO impedes charge extraction. Furthermore, it is found that a low ETM mobility leads to charge accumulation in the perovskite under short-circuit conditions. However, thisalone cannot explain the remarkably high short-circuit QFLS of over 1 eV which is observed in all devices. Instead, drift-diffusion simulations allow this effect to be assigned to the presence of mobile ions which screen the internal electric field at short-circuit and lead to a reduction in the short-circuit current density by over 2 mA cm⁻² in the best device.

Publication date: October 2023

Source: Nano Energy, Volume 115

Author(s): Zhifang Wu, Enbing Bi, Luis K. Ono, Dengbing Li, Osman M. Bakr, Yanfa Yan, Yabing Qi

A multi-fluorine-containing higher fullerene-porphyrin dyad (F₇₀PD) is synthesized and applied to regulate the crystal orientation and the buried interface defects of the perovskite film. The robust interface engineering not only reduces the non-radiative recombination in bulk and interface of the perovskite layer but also increases the activation energy of ion migration, enabling efficient and stable perovskite solar cells.

Abstract

Perovskite films prepared by the solution process usually result in irregular grain orientation and rich buried interface defects, hindering the further improvement of device performance. Herein, multi-fluorine-containing C₆₀- and C₇₀ (higher fullerene)-porphyrin derivatives, F₆₀PD and F₇₀PD, are synthesized and pre-buried to modify the SnO₂/perovskite heterointerface. The F₇₀PD modification layer provides a better perovskite quality and more effective electron transporting capability compared to the corresponding F₆₀PD, with the F₇₀PD being more effective in regulating the perovskite growth, passivating the buried interface defects, and optimizing the interface energy level alignment. Consequently, the F₇₀PD-based device delivers superior efficiency and stability than the control and F₆₀PD-based devices. The F₇₀PD-based device yields a champion efficiency of 24.09% with negligible hysteresis. Meanwhile, due to the increased activation energy of ion migration, the F₇₀PD-based device maintains 80% of its initial efficiency after operating at the maximum power point for 1620 h. This study highlights the potential of designing higher fullerene materials for buried interface to further improve the perovskite solar cells’ performance.

A high curvature PEDOT:PSS transport layer is used to improve the charge transport balance level in perovskite light emitting diodes. This high curvature property effectively increases the surface charge density of the local field through the dielectric confinement effect, thus promoting the effective injection of holes, which is significant for the enhancement of device performance.

Abstract

The rapidly developed metal halide perovskite light-emitting diodes (PeLEDs) are considered as a promising candidate for next-generation display and illumination, but the unbalanced charge transport is still a hard-treat case to restrict its efficiency and operational stability. Here, a high curvature PEDOT:PSS transport layer is demonstrated via the self-assembly island-like structures by the incorporation of alkali metal salts. Benefiting from the dielectric confinement effect of the high curvature surface, the modified CsPbBr₃-based PeLEDs present a 2.1 times peak external quantum efficiency (EQE) from 6.75% to 14.23% and a 3.3 times half lifetime (T ₅₀) from 3.96 to 13.01 h. Besides, the PeLEDs show high luminance up to 44834 cd m⁻². Evidently, this work may provide a deep insight into the structure-activity relationship between the micro-structures at the PEDOT:PSS/perovskite interface and the performance of PeLEDs, and crack the codes for ameliorating the performance of PeLEDs via interfacial micro-structured regulation.

The co-solvent strategy to disassemble the micelles formed by the amphiphilic self-assembled monolayer (SAM) molecules is introduced. The pre-disassembly of micelles reduces the energetic barrier to form a densely packed SAM. This strategy universally enhances the power conversion efficiencies (PCEs) of PSCs based on MeO-2PACz, 2PACz, and CbzNaph SAM hole-selective layers. The champion device based on the CbzNaph processed from co-solvent achieves a high PCE of 24.98% with an impressive fill factor of 85.06%.

Abstract

Self-assembled monolayers (SAMs) are widely employed as effective hole-selective layers (HSLs) in inverted perovskite solar cells (PSCs). However, most SAM molecules are amphiphilic in nature and tend to form micelles in the commonly used alcoholic processing solvents. This introduces an extra energetic barrier to disassemble the micelles during the binding of SAM molecules on the substrate surface, limiting the formation of a compact SAM. To alleviate this problem for achieving optimal SAM growth, a co-solvent strategy to disassemble the micelles of carbazole-based SAM molecules in the processing solution is developed. This effectively increases the critical micelle concentration to be above the processing concentration and enhances the reactivity of the phosphonic acid anchoring group to allow densely packed SAMs to be formed on indium tin oxide. Consequently, the PSCs derived from using MeO-2PACz, 2PACz, and CbzNaph SAM HSLs show universally improved performance, with the CbzNaph SAM-derived device achieving a champion efficiency of 24.98% and improved stability.

Polylactic acid (PLA) is used to modify mixed-halide inorganic perovskites. PLA can passivate the defects and induce n-type to p-type transition, favoring charge transfer from perovskite to hole transport layer, thus improving the device performance. Record power conversion efficiencies of 19.12% and 18.05% are achieved for CsPbI_2.25Br_0.75 and CsPbI₂Br solar cells, respectively.

Abstract

Inorganic perovskite solar cells (PSCs) suffer from serious carrier recombination and open-circuit voltage loss because of surface defects and unfavorable energy level alignment. Herein, a polylactic acid (PLA) modification approach to improve the performance of mixed-halide inorganic perovskites is reported. First, the surface defects are effectively passivated through strong interaction between C═O in PLA and undercoordinated Pb²⁺. Second, secondary grain growth is induced by PLA modification, resulting in larger grain sizes. Third, PLA modification makes the surface region of perovskite change from n- to p-type, favoring charge transport from perovskite to the hole transport layer (HTL). The PLA modified films enable PSCs with less nonradiative recombination and lower energy loss. Consequently, record PCEs of 19.12% and 18.05% are achieved for CsPbI_2.25Br_0.75 and CsPbI₂Br PSCs, respectively. The PSC with an active area of 1 cm² shows a PCE of 16.41%. A PCE of 14.70% is achieved for HTL-free PSC with carbon electrode. In addition, the PSC with PLA modification shows significantly improved air stability due to the hydrophobic PLA coating. This work suggests that PLA surface modification is an effective approach to achieving efficient, stable, scalable, and low-cost inorganic PSCs.