Ligang Yuan

Publication date: 16 March 2022

Source: Joule, Volume 6, Issue 3

Author(s): Xiyue Yuan, Yunli Zhao, Dongsheng Xie, Langheng Pan, Xinyuan Liu, Chunhui Duan, Fei Huang, Yong Cao

A new concept of oligomer-assisted high-performance organic solar cells (OSCs) was proposed. Developing the oligomer-assisted OSCs is a facile and general strategy with the combination of the advantages of both binary and ternary devices, which enables >18 % device efficiency together with improved stability.

Abstract

Although ternary organic solar cells (OSCs) have unique advantages in improving device performance, the morphology assembly in the ternary-phase would be more uncertain or complex than that in the binary-phase. Here, we propose a new concept of oligomer-assisted photoactive layers for high-performance OSCs. The formed alloy-like phase of the oligomer : host polymer blend enabled the oligomer-assisted OSCs to fuse the advantages of both binary and ternary devices, exhibiting substantially enhanced performance and stability compared to the control devices. With the addition of oligomers, outstanding efficiencies of 17.33 % for a PM6 : Y6 device, 18.32 % for a PM6 : BTP-eC9 device, and 17.13 % for a PM6/Y6 pseudo-bilayer device were achieved, all of which are one of the highest values in their corresponding fields. The improved performance originated from the downshift energy levels, enhanced light absorption, optimized blend morphology, favorable charge dynamics, and reduced non-radiative energy loss.

This review summarizes the recent advances of SnO₂-based perovskite solar cells (PSCs) and the related interface optimization strategies and applications. The fundamental properties of SnO₂ are discussed, with a focus on the defect chemistry, and various preparation methods for improving SnO₂ and SnO₂/perovskite interface. Finally, the challenges and opportunities for further development of SnO₂-based PSCs are provided.

Abstract

Perovskite solar cells (PSCs) based on the regular n–i–p device architecture have reached above 25% certified efficiency with continuously reported improvements in recent years. A key common factor for these recent breakthroughs is the development of SnO₂ as an effective electron transport layer in these devices. In this article, the key advances in SnO₂ development are reviewed, including various deposition approaches and surface treatment strategies, to enhance the bulk and interface properties of SnO₂ for highly efficient and stable n–i–p PSCs. In addition, the general materials chemistry associated with SnO₂ along with the corresponding materials challenges and improvement strategies are discussed, focusing on defects, intrinsic properties, and impact on device characteristics. Finally, some SnO₂ implementations related to scalable processes and flexible devices are highlighted, and perspectives on the future development of efficient and stable large-scale perovskite solar modules are also provided.

In this review, the progress of wide-bandgap organic–inorganic hybrid perovskite solar cells (PSCs) are initially summarized and the issues of phase segregation and voltage loss are assessed. Then, the diverse applications of wide-bandgap PSCs in semitransparent devices, indoor photovoltaics, and tandem devices are discussed and their challenges and perspectives are evaluated.

Abstract

Under the groundswell of calls for the industrialization of perovskite solar cells (PSCs), wide-bandgap (>1.7 eV) mixed halide perovskites are equally or more appealing in comparison with typical bandgap perovskites when the former's various potential applications are taken into account. In this review, the progress of wide-bandgap organic–inorganic hybrid PSCs—concentrating on the compositional space, optimization strategies, and device performance—are summarized and the issues of phase segregation and voltage loss are assessed. Then, the diverse applications of wide-bandgap PSCs in semitransparent devices, indoor photovoltaics, and various multijunction tandem devices are discussed and their challenges and perspectives are evaluated. Finally, the authors conclude with an outlook for the future development of wide-bandgap PSCs.

A perovskite homojunction is constructed and its stability is characterized. In the homojunction, doping defects tend to compensate each other through interdiffusion, resulting in the weakening of the built-in electric field. Herein, phenethylammonium iodide is used to inhibit the defects diffusion, improving the stability of the perovskite homojunction and related solar cells.

Perovskite homojunction can promote the separation and oriented transportation of the photocarriers through the built-in electric field, and weaken the dependence of solar cells on the charge transport layer. Although the perovskite homojunction shows great advantages in improving device efficiency, it retains the inherent poor stability of perovskite materials. Herein, it is found that donor defects (MA⁺ interstitial, I⁻ vacancy, etc.) in the n-type layer are prone to compensate the acceptor defects (MA⁺ vacancy, I⁻ interstitial, etc.) in the p-type layer. This compensation behavior results from the diffusion of doping defects driven by a concentration gradient, which leads to the weakening of the built-in electric field. Furthermore, phenethylammonium iodide is introduced into the perovskite homojunction to inhibit the defect diffusion, which enhances the stability of the homojunction and the corresponding solar cells. After modification, the efficiency of perovskite homojunction solar cells is improved from 8.60% to 9.60%, and retains 80% (standard ≈30%) of initial efficiency after 1000 h aging.

Modified NiOx Films

In article number 2100700, Annalisa Bruno and co-workers discussed a variety of surface modifications and their impacts on the structural and optoelectronic properties of the NiOx. The main alteration strategies are based on physical (UV-ozone, oxygen, argon, and/or helium plasma), chemical (interlayer passivation), and doping treatments. The effects of modified NiOx films on the power conversion efficiency and stability of p-i-n perovskite solar cells have been analyzed. Finally, the current challenges and future outlooks have also been discussed.

COTIC-4F: PC₆₁BM: PTB7-Th together with CsPbCl₃:Yb³⁺, Ce³⁺, Cr³⁺ nanophosphors are integrated into perovskite solar cells (PSCs). The near-infrared spectral response is extended to 1100 nm. The power conversion efficiency increases significantly from 20.52% to 23.40%. This work represents an effective and general strategy for obtaining efficient and stable PSC devices with extremely broad spectral responses.

Abstract

Extending near-infrared (NIR) spectral response and increasing ultraviolet utilization is still a challenge in the context of improving power conversion efficiency (PCE) for perovskite solar cells (PSCs). In this work, to extend NIR light-harvesting of PSCs, a novel COTIC-4F: PC₆₁BM: PTB7-Th ternary organic bulk-heterojunction together with Au nanotriangles is integrated on the PSCs. The NIR spectral response is thus extended to 1100 nm. In fact, the COTIC-4F: PC₆₁BM: PTB7-Th layer enables multi-functional effects, which can serve as electron transport, trap passivation, and moisture barrier layer in addition to NIR light harvesting. For increasing UV utilization, CsPbCl₃:Yb³⁺, Ce³⁺, Cr³⁺ nanophosphors with photoluminescent quantum yield close to 200% are fabricated, which demonstrate excellent down-conversion ability. Then, CsPbCl₃: Yb³⁺, Ce³⁺, Cr³⁺/polymethylmethacrylate composite films are self-assembled on a hybrid device, resulting in a 6.2% relative enhancement of short circuit current density. After simultaneously improving the NIR and UV spectral response of device, the PCE is increased significantly from 20.52% to 23.40% and the Jsc is increased from 21.79 to 25.96 mA cm⁻², representing one of the highest PCE and maximum Jsc enhancements in the reported inverted hybrid organic/PSCs. This work represents an effective and general strategy for obtaining efficient and stable PSC devices with extremely broad spectral responses.

In situ growth of single crystal thin films (SCTFs) on hole transport layers (HTLs) is of paramount importance for developing high-performance optoelectronic devices. Here, hidden growth mechanism for MAPbBr₃ SCTFs on HTLs is unraveled and high-quality MAPbBr₃ SCTFs with record largest area to thickness ratio are obtained through modulating three main factors: interface energy, precursor solution concentration, and heating rate.

Abstract

The development of in situ growth methods for the fabrication of high-quality perovskite single-crystal thin films (SCTFs) directly on hole-transport layers (HTLs) to boost the performance of optoelectronic devices is critically important. However, the fabrication of large-area high-quality SCTFs with thin thickness still remains a significant challenge due to the elusive growth mechanism of this process. In this work, the influence of three key factors on in situ growth of high-quality large-size MAPbBr₃ SCTFs on HTLs is investigated. An optimal “sweet spot” is determined: low interface energy between the precursor solution and substrate, a slow heating rate, and a moderate precursor solution concentration. As a result, the as-obtained perovskite SCTFs with a thickness of 540 nm achieve a record area to thickness ratio of 1.94 × 10⁴ mm, a record X-ray diffraction peak full width at half maximum of 0.017°, and an ultralong carrier lifetime of 1552 ns. These characteristics enable the as-obtained perovskite SCTFs to exhibit a record carrier mobility of 141 cm² V⁻¹ s⁻¹ and good long-term structural stability over 360 days.

A comprehensive optimization strategy, including 2-phenylethylammonium ligand (PEA⁺)-passivated FAPbI₃ quantum dots (QDs), synergistic coverage effects between the QDs and hole-transporting layers, and effective electron-transporting layers for constructing a feasible device structure leads to a high-efficiency near-infrared (NIR) QD-based light-emitting diode (QLED) centered at 772 nm and exhibiting a maximum external quantum efficiency up to 15.4%, the highest external quantum efficiency recorded for perovskite-based NIR QLEDs.

Abstract

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI₃ QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI₃ QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λ_max at 772 nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54 mA cm⁻² (2.6 V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.

Publication date: 15 June 2022

Source: Chemical Engineering Journal, Volume 438

Author(s): Haoxin Wang, Mengmeng Zheng, Cheng Chen, Wei Zhang, Biyi Wang, Chuansu Yang, Mengde Zhai, Hui Xu, Ming Cheng

Publication date: 15 June 2022

Source: Chemical Engineering Journal, Volume 438

Author(s): Jin Li, Xin Zhou, Congcong Wu, Li Zhao, Binghai Dong, Shimin Wang, Bo Chi

Publication date: 20 April 2022

Source: Joule, Volume 6, Issue 4

Author(s): Xiuhong Sun, Zhipeng Shao, Zhipeng Li, Dachang Liu, Caiyun Gao, Chen Chen, Bingqian Zhang, Lianzheng Hao, Qiangqiang Zhao, Yimeng Li, Xianzhao Wang, Yue Lu, Xiao Wang, Guanglei Cui, Shuping Pang

Aiming for hybrid perovskite solar cells, a novel strategy is developed that using ethylenediamine diiodide and phenethylammonium iodide as co-modifiers to selectively targeting anchor with lead–tin binary perovskite materials, resulting in comprehensively healing the dual-sourced defects. As a result, a champion efficiency of 22.51% is achieved, which is the record efficiency among the ideal-bandgap perovskite solar cells.

Abstract

Mixed lead–tin perovskite solar cells (LTPSCs) with an ideal bandgap are demonstrated as a promising candidate to reach higher power conversion efficiency (PCE) than their Pb-counterparts. Herein, a Br-free mixed lead–tin perovskite material, FA_0.8MA_0.2Pb_0.8Sn_0.2I₃, with a bandgap of 1.33 eV, as a perovskite absorber, is selected. Through density functional theory calculations and optoelectronic techniques, it is demonstrated that both Pb- and Sn-related A-site vacancies are pushed into deeper energetic depth, causing severe nonradiative recombination. Hence, a selective targeting anchor strategy that employs phenethylammonium iodide and ethylenediamine diiodide as co-modifiers to selectively anchor with Pb- and Sn-related active sites and passivate bimetallic traps, respectively, is established. Furthermore, the selectivity of the molecular oriented anchor passivation is demonstrated through energetic depth specificity of Pb- and Sn-related traps. As a result, a substantially enhanced open-circuit voltage (V _OC) from 0.79 to 0.90 V for the LTPSCs is achieved, yielding a champion PCE of 22.51%, which is the highest PCE among the reported ideal-bandgap PSCs. The V _OC loss is reduced to 0.43 V.

The crystal growth in 2D/3D perovskite films is regulated by introducing a 2D (NpMA)₂PbI₄ perovskite or NpMAI into the PbI₂ precursor solutions using a two-step deposition method. The optimized film shows much enlarged grain size and significantly reduced trap density, which enables a champion efficiency of 24.37% for a 0.10 cm⁻² device and 22.26% for a 1.01 cm⁻² device.

Abstract

Reducing the electronic defects in perovskite films has become a substantial challenge to further boost the photovoltaic performance of perovskite solar cells. Here, 2D (NpMA)₂PbI₄ perovskite and 1-naphthalenemethylammonium iodide (NpMAI) are separately introduced into the PbI₂ precursor solutions to regulate the crystal growth in a 2D/3D perovskite film using a two-step deposition method. The (NpMA)₂PbI₄ modulated perovskite film shows a significantly improved film quality with enlarged grain size from ≈500 nm to over 1000 nm, which greatly reduces the grain-boundary defects, improves the charge carrier lifetime, and hinders ionic diffusion. As a result, the best-performing device shows a high power conversion efficiency (PCE) of 24.37% for a small-area (0.10 cm⁻²) device and a superior PCE of 22.26% for a large-area (1.01 cm⁻²) device. Importantly, the unencapsulated device shows a dramatically improved operational stability with maintains over 98% of its initial efficiency after 1500 h by maximum power point (MPP) tracking under continuous light irradiation.

Low-temperature-processed perovskite solar cells have wide applicability in flexible and two-terminal tandem devices. In this review, recent breakthroughs in low-temperature-processed stable perovskite device architectures are summarized. A wide range of topics starting with degradation processes, stability-enhanced material developments, general trends, and process upscaling of notable low-temperature-processed materials are summarized.

Abstract

The impending commercialization of perovskite solar cells (PSCs) is plodding despite the booming power conversion efficiencies and high stabilities. Most high-performance, stable PSCs are often processed partially with high-temperature processes, increasing the cost of production and energy payback time. Low-temperature-processed PSCs are crucial as they cut down the expenses lowering the barriers to industrial use. In addition, low-temperature-processed methods have a wide range of applicability in flexible devices and for tandem applications with other photovoltaic technologies where the temperature budget is limited. Therefore, making stable PSCs under ambient conditions as well as providing low-cost fabrication techniques is highly desirable. Here, a detailed review is presented on the development of the low-temperature process strategies for fabricating highly stable PSCs and perovskite solar modules. The effectiveness of low-temperature processing in various classes of materials is also discussed. First, the authors introduce some major degradation processes in PSCs. Then, the developments and evolving strategies of notable materials using low-temperature processing routes and a correlation with stability are summarized. A few general trends which are related to stability are also discussed. Overall, this review contributes to a better understanding of the status of low-temperature-processed cells and modules.

Herein, a comprehensive review on the recent progress of pure FAPbI₃-based perovskite solar cells (PSCs) is presented. From the development in both efficiency and stability, improvement on the FAPbI₃ film quality including morphology control, defect passivation, dimensional regulation, and strain engineering as well as optimization of the device structure and interface layers promotes the commercialization process of pure FAPbI₃-based PSCs.

Organic–inorganic hybrid perovskite solar cells (PSCs) have attracted great attentions due to their rapid increase of power conversion efficiency (PCE). Although the highest PCE of PSCs (25.7%) has been achieved via using formamidinium lead iodide (FAPbI₃) with a suitable bandgap, there is still a lack of systematic analysis on FAPbI₃-based PSCs toward high stability and high efficiency. Herein, the progress in FAPbI₃ films and achievements in their high-efficiency and long-term stability PSCs are comprehensively reviewed. First, the progress from the aspects of morphology, defect, dimension, and strain for FAPbI₃ film optimization is summarized and then the development of FAPbI₃ PSCs in both efficiency and stability is discussed. Then, the methods to improve the FAPbI₃ film quality by morphology control, defect passivation, dimensional regulation, and strain engineering, as well as strategies to optimize the device structure and interface layers, which are critical to promote device stability and efficiency, are evaluated. Finally, the outlook and strategies for realizing commercialized FAPbI₃ PSCs with high efficiency and long lifetime are discussed.

The effect of charge transport material on the overall optical performance of the device is examined by finite element method. Density functional theory calculates the microstructure of the charge transport layer material and comprehends the energy level matching of the device. Combining micro- and macroscales facilitates the development of high-efficiency perovskite solar cells.

CsPbBr₃ film possesses high stability and easy manufacturing characteristics, rendering it attractive for applications in perovskite solar cells (PSCs). However, optical loss and energy level matching of different material layers are still the major factors, limiting the performance of PSCs. Herein, the finite element method (FEM) and density functional theory (DFT) calculations composed of simulation interaction technology are used to study the effects of different electron transport layer and hole transport layer materials on the optical performance of different PSC configurations. The effect of the charge transport layer (CTL) material and CsPbBr₃ on the energy level matching and charge transport of the device is explained. The FEM simulation results show that inorganic CTL materials produce less parasitic absorption than the organic materials. The DFT calculation results give the microscopic design rules of the CTL material. In addition, PSCs with a light-trapping structure are designed, which effectively suppressed surface reflection. Finally, through the screening of CTL materials and the design of advanced light-trapping structures, the photocurrent of PSCs is increased by 69.8% (from 5.30 to 9.00 mA cm⁻²). This work provides a novel model for the screening of CTL materials for inorganic PSCs.

TEASCN (2-thiopheneethylamine thiocyanate) was synthesized to construct a bilayer structure on a Sn-Pb perovskite surface, which can passivate perovskite and ensure effective carrier transfer, enabling the device to reach a certified efficiency of 21.1 %. The mechanism for the growth of the uniform bilayer structure is revealed by simulation based on density functional theory.

Abstract

The combination of comprehensive surface passivation and effective interface carriers transfer plays a critical role in high-performance perovskite solar cells. A 2D structure is an important approach for surface passivation of perovskite film, however, its large band gap could compromise carrier transfer. Herein, we synthesize a new molecule 2-thiopheneethylamine thiocyanate (TEASCN) for the construction of bilayer quasi-2D structure precisely on a tin-lead mixed perovskite surface. This bilayer structure can passivate the perovskite surface and ensure effective carriers transfer simultaneously. As a result, the open-circuit voltage (V _oc) of the device is increased without sacrificing short-circuit current density (J _sc), giving rise to a high certified efficiency from a credible third-party certification of narrow band gap perovskite solar cells. Furthermore, theoretical simulation indicates that the inclusion of TEASCN makes the bilayer structure thermodynamically more stable, which provides a strategy to tailor the number of layers of quasi-2D perovskite structures.

Publication date: 16 March 2022

Source: Joule, Volume 6, Issue 3

Author(s): Yiming Li, Zijing Chen, Bingcheng Yu, Shan Tan, Yuqi Cui, Huijue Wu, Yanhong Luo, Jiangjian Shi, Dongmei Li, Qingbo Meng

Two donor–acceptor (DA) covalent organic frameworks (COFs) show high crystallinity, good porosity, and excellent stability, which are incorporated into the FAPbI₃ layer of perovskite solar cells. The highest power-conversion efficiency observed for perovskite solar cells constructed with DA-COFs is 23.19% with excellent humidity stability, which provides a pathway for using DA-COFs to fabricate perovskite solar cells with high efficiency and stability.

Abstract

Covalent organic frameworks (COFs) as a new class of crystalline, porous materials have attracted extensive attention in the fields of photocatalytic and photovoltaic applications. Generally, donor–acceptor (DA) structures play an important role in the charge separation efficiency of solar cells. In this study, two DA-COFs with high crystallinity, good porosity, and excellent stability are incorporated into the FAPbI₃ layer of perovskite solar cells. This addition of DA-COFs reduces the defect concentration and shallows the defect state. The donor–acceptor system in COFs also possesses strong charge-transfer pathway, which strongly prevents charge recombination to afford more efficient charge separation efficiency. The highest power-conversion efficiency of perovskite solar cells constructed with DA-COFs is 23.19% with excellent humidity stability of the solar cells. Therefore, this work provides a pathway for using DA-COFs to fabricate perovskite solar cells with higher efficiency and stability.

A solid n-PEDOT:POM powder with neutral pH is synthesized by utilizing polyoxometalate as an oxidizing reagent, which exhibits excellent water solubility, high chemical stability and superior hole collection ability. Organic solar cells (OSCs) with n-PEDOT:POM as a hole transport layer exhibit a photovoltaic efficiency of 17.62% with a fill factor of 0.80. In addition, the neutral pH of PEDOT:PSS effectively improves the long-term stability of OSCs.

Abstract

Although PEDOT:PSS is the most prominently used conducting polymer as hole transporting layer (HTL) material in organic solar cells (OSCs), the strong acidity of PEDOT:PSS has been proved to cause corrosion on electrodes, which is largely responsible for device instability. At present, the development of a non-corrosive and stable PEDOT with comparable performance to PEDOT:PSS remains a great challenge in the field. Herein, a solid n-PEDOT:POM powder with neutral pH is synthesized by utilizing polyoxometalate (POM) as an oxidizing reagent, which exhibits excellent water solubility, high chemical stability, and superior hole collection ability. Impressively, an amazing fill factor of 0.80 along with a photovoltaic efficiency of 17.62% is obtained in the OSC by using n-PEDOT:POM as the HTL, suggesting an exceptional hole collection ability for n-PEDOT:POM. In addition, the neutral pH of PEDOT:PSS effectively improves the long-term stability of OSCs. X-ray photoelectron spectroscopy results reveal that, compared to the electrode/PEDOT:PSS interface, the permeation of dissociative indium from the electrode to n-PEDOT:POM can be greatly retarded, which proves the non-corrosive effect of n-PEDOT:POM and its improvement of device stability. The successful preparation of a non-corrosive and stable PEDOT derivative without sacrificing its hole collection ability provides the most fruitful new insight into developing high-performance HTL materials.

Publication date: 1 June 2022

Source: Chemical Engineering Journal, Volume 437, Part 1

Author(s): Xiaobing Cao, Lei Hao, Zijin Liu, Gengyang Su, Xin He, Qingguang Zeng, Jinquan Wei

Publication date: 1 June 2022

Source: Chemical Engineering Journal, Volume 437, Part 2

Author(s): Gizachew Belay Adugna, Seid Yimer Abate, Yu-Tai Tao

A seed-assisted crystallization approach is demonstrated through addition of alkali salts for enabling homogeneous and highly crystalline large-area perovskite films via scalable slot-die coating technique. The slot-die coated methylammonium-free perovskite module with an active area of 57.5 cm² shows an efficiency of 16.22% and retains 82% of its initial efficiency after 4800 h under 30% RH without encapsulation.

Abstract

Typical fabrication methods for laboratory-scale (<1 cm²) perovskite solar cells (PSCs) are undeniably not scalable and the control of crystallization of large-area perovskite layer for commercial sized modules is also particularly challenging. Here, a seed-assisted crystallization approach is demonstrated through addition of alkali salts, CsPbBr₃ and KPb₂Br₅, to the perovskite precursor ink for enabling homogeneous and highly crystalline large-area Cs_0.15FA_0.85Pb(I_0.83Br_0.17)₃ (CsFA) perovskite films via scalable slot-die coating technique. X-ray photoelectron spectroscopy analysis reveals the segregation of potassium ions at SnO₂/perovskite interface which serve as nucleation sites for the crystallization of perovskite layer. The uniformly slot-die coated CsFA films (100 cm²) from the additives containing precursor inks possess larger grains with enhanced optoelectronic properties and the corresponding devices display higher reproducibility and consistency. A champion device efficiency of 18.94% under 1 sun illumination for slot-die coated PSCs in n-type/intrinsic/p-type structure is demonstrated with improved stability with 82% of its initial efficiency tested at 65 °C for 1150 h. The slot-die coated methylammonium-free perovskite module with an active area of 57.5 cm² shows an efficiency of 16.22% and retains 82% of its initial efficiency after 4800 h under 30% relative humidity without encapsulation.