Mahui

Ag nanorods aqueous solution is introduced to the perovskite absorber layer to enhance the power conversion efficiency from 18.5% to 20.29%, with fill factors close to 82%. Ag nanorods increase light absorption by the local surface plasmon resonance effect, and the presence of water leads to high‐quality perovskite films by inducing recrystallization.

Perovskite solar cells (PSCs) have been widely studied during the past 10 years. Albeit the excellent light‐absorption ability, the thickness of the perovskite layer is limited to maintain effective control over morphology and carrier migration. Meanwhile, the quality of perovskite films is a crucial factor affecting the performance of final devices. The traditional one‐step process for preparing triple‐cation perovskite films suffers from small grain size, low crystallization quality, and many surface defects. Herein, in the process of triple‐cation perovskite‐based solar cells, a facile dosing strategy of a silver nanorods (AgNR) aqueous solution into the perovskite precursor is adopted. The localized surface plasmon resonance effect of AgNR enhances the light‐capture ability of the perovskite layer without increasing the thickness. At the same time, the presence of appropriate water helps to obtain high‐quality perovskite films with larger grain size and fewer defects. It is found that the synergy of AgNR and water successfully reduces the defect density and increases mobility significantly. Consequently, a power conversion efficiency of 20.18% and a short‐circuit current (J _SC) of 22.08 mA cm⁻² is achieved. Meanwhile, an excellent fill factor beyond 82% is reported, which is one of the highest values for triple‐cation hybrid PSCs.

The studies from the steady‐state and time‐dependent measurements indicate that the extended absorption range, short charge carrier extraction time, and high charge carrier mobility by the non‐fullerene electron acceptors in the photoactive layer are responsible for enhanced photocurrent in ternary organic solar cells.

Ternary organic solar cells, a single active layer comprising three different components, are demonstrated to be one of the most efficient ways to approach high‐performance organic solar cells. But nevertheless, most of the ternary organic solar cells are characterized by steady‐state measurements, which are helpful but inadequate to fully understand the underlying charge carrier behavior at a short time scale. Herein, a comparison of the steady‐state and time‐dependent measurements is used to investigate the functionality of non‐fullerene electron acceptors in ternary organic solar cells. The steady‐state measurements indicate that non‐fullerene electron acceptors enlarge the absorption range of the photoactive layer, suppress charge carrier recombination, reduce charge carrier transfer resistance, and thereby increase photocurrent in ternary organic solar cells. The time‐dependent measurements demonstrate that a short charge carrier extraction time and a high charge carrier mobility are responsible for enhanced photocurrent in ternary organic solar cells. A comprehensive method understanding the underlying of enhanced efficiency of ternary organic solar cells is provided herein.

The fused‐ring acceptor IT‐M is added into an unfused‐core acceptor‐based binary blend of PBDB‐TF:HC‐PCIC. Notable fill factor enhancement and a broad compositional tolerance are achieved for the ternary solar cells. Thus, the power conversion efficiency is significantly improved from 11.14% for binary devices to 12.34% for ternary cells.

The ternary blend strategy has shown great potential to improve the photovoltaic performance of organic solar cells (OSCs). Usually, adopting two acceptors with similar chemical structures shows good compatibility but limited enhancement in performance, whereas adopting two acceptors with different chemical structures always has a compositional sensitivity issue. Herein, a highly efficient ternary OSC with an enhanced fill factor (FF) and a broad compositional tolerance is demonstrated by introducing the fused‐ring acceptor IT‐M to a binary blend based on an unfused‐core acceptor HC‐PCIC and polymer donor PBDB‐TF. Detailed studies on the optical, electrical, and morphological properties of ternary blends reveal the process of charge dynamics and work mechanisms in the ternary device. It is found that the addition of IT‐M into the PBDB‐TF:HC‐PCIC binary blend not only adapts to the parallel‐like model, but also optimizes the morphology and domain sizes in the ternary blend, resulting in a reduced trap‐assisted recombination and suppressed bimolecular recombination. Consequently, open‐circuit voltage (V _oc), short‐circuit current density (J _sc), and FF are synergistically enhanced, leading to an improved power conversion efficiency (PCE) of 12.34% with a high V _oc of 0.88 V, an increased J _sc of 18.69 mA cm⁻², and an enhanced FF of 73.82% for the ternary device with 5% IT‐M content. Moreover, the PCEs of ternary OSCs remain above 11% within an IT‐M ratio of 2.5–50%, exhibiting a broad compositional tolerance, which is rarely reported in fullerene‐free ternary OSCs.

Herein, a facile method to improve the long‐term stability of perovskite solar cells using N719 dye molecules as additives is presented. Perovskite‐dye hybrid films show better crystallinity, enhanced light absorption, and boosted moisture stability. Due to the greatly retarded hydration process, the degradation process of perovskite‐dye solar cells is three times longer than that for pristine devices.

Metal‐halide perovskite solar cells (PSC) have shown great success in achieving high efficiencies but less satisfaction in achieving long‐term stability. Perovskites are prone to forming perovskite hydrates in humid environments, which leads to the decomposition of the perovskite materials. Herein, a common and cheap dye molecule, called cis‐di(thiocyanato)bis(2,2‐bipyridyl4,4‐dicarboxylate)ruthenium(II), denoted as N719, is introduced into mixed‐cation mixed‐halide perovskites for better moisture stability. It is discovered that the N719 molecules form perovskite‐dye complexes in the precursor solution, leading to larger grains and better film crystallinity by slowing down the crystallization process. Fourier‐transform infrared spectroscopy and X‐ray diffraction characterizations suggest that the N719 molecules exist in the crystallized perovskite films but are not incorporated into the perovskite crystal lattice. The presence of N719 molecules in perovskite films greatly retards the formation of perovskite hydrates due to a three‐times‐increased water migration barrier. Owing to these improvements, nonencapsulated N719‐PSC retain over 80% of their original efficiencies after aging under a high relative humidity of 60% for 250 h, which is three times longer than that for pristine cells. A cheap and effective route for controlling the perovskite crystallization process and improving the stability of PSC without sacrificing device efficiency is represented.

Homojunction bilayer electron transport layers (ETLs) are developed by stacking Sb‐doped SnO₂ (Sb‐SnO₂) and SnO₂ ETLs via a low‐temperature process. The perovskite solar cells with the Sb‐SnO₂/SnO₂ bilayer ETLs achieve the best power conversion efficiency of 20.73%. Due to Sb‐SnO₂/SnO₂, the bilayer ETL with a cascade energy arrangement enhances charge separation and reduces carrier recombination.

Energy alignment between electron transport layers (ETLs) and perovskite has a strong influence on the device performance of perovskite solar cells (PSCs). Two approaches are deployed to tune the energy level of ETLs: 1) doping ETLs with aliovalent metal cations and 2) constructing heterojunction bilayers with different materials. However, the abrupt interfaces in the heterojunction bilayers introduce undesirable carrier recombination. Herein, a homojunction bilayer ETL is developed by stacking Sb‐doped SnO₂ (Sb‐SnO₂) and SnO₂ ETLs via low‐temperature spin‐coating processes. The energy levels of ETLs are tuned by the incorporation of Sb and altering stacking orders. Bilayer ETL of Sb‐SnO₂/SnO₂ with cascade energy alignment promotes the best power conversion efficiency of 20.73%, surpassing single‐layer ETLs of SnO₂ (18.23%) and Sb‐SnO₂ (19.15%), whereas the SnO₂/Sb‐SnO₂ bilayer with barricade energy alignment receives the poorest device performance. The cascade bilayer ETL facilitates charge separation and suppresses carrier recombination in PSCs, which is verified by photoluminescence, conductivity, and impedance characterizations. The homojunction bilayer ETLs with adjustable energy levels open a new direction for interface engineering toward efficient PSCs.

Publication date: November 2019

Source: Nano Energy, Volume 65

Author(s): In Young Choi, Chan Ul Kim, Wonjin Park, Hyungmin Lee, Myoung Hoon Song, Kuen Kee Hong, Sang Il Seok, Kyoung Jin Choi

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The spintronic properties of different hybrid organic–inorganic perovskites (HOIPs) are studied in spin valve devices, including spin diffusion length and spin lifetime, as well as the impact of the chemical components on these properties. This study aims at demonstrating promising spintronic applications of HOIPs, and providing a clear path for engineering spintronic devices based on HOIPs.

Abstract

The hybrid organic–inorganic perovskites (HOIPs) form a new class of semiconductors which show promising optoelectronic device applications. Remarkably, the optoelectronic properties of HOIP are tunable by changing the chemical components of their building blocks. Recently, the HOIP spintronic properties and their applications in spintronic devices have attracted substantial interest. Here the impact of the chemical component diversity in HOIPs on their spintronic properties is studied. Spin valve devices based on HOIPs with different organic cations and halogen atoms are fabricated. The spin diffusion length is obtained in the various HOIPs by measuring the giant magnetoresistance (GMR) response in spin valve devices with different perovskite interlayer thicknesses. In addition spin lifetime is also measured from the Hanle response. It is found that the spintronic properties of HOIPs are mainly determined by the halogen atoms, rather than the organic cations. The study provides a clear avenue for engineering spintronic devices based on HOIPs.

A high power conversion efficiency of 11.76%, the best efficiency for all‐polymer solar cells, is achieved by printing fabrication based on PTzBI‐Si:N2200 processing with 2‐methyltetrahydrofuran. A Multi‐length‐scaled morphology is found in the bulk heterojunctions, which ensures fast transfer of carriers and facilitates exciton separation, and boosts carrier mobility and current density, thus improving the device performance.

Abstract

All‐polymer solar cells (all‐PSCs) exhibit excellent stability and readily tunable ink viscosity, and are therefore especially suitable for printing preparation of large‐scale devices. At present, the efficiency of state‐of‐the‐art all‐PSCs fabricated by the spin‐coating method has exceeded 11%, laying the foundation for the preparation and practical utilization of printed devices. A high power conversion efficiency (PCE) of 11.76% is achieved based on PTzBI‐Si:N2200 all‐PSCs processing with 2‐methyltetrahydrofuran (MTHF, an environmentally friendly solvent) and preparation of active layers by slot die printing, which is the top efficient for all‐PSCs. Conversely, the PCE of devices processed by high‐boiling point chlorobenzene is less than 2%. Through the study of film formation kinetics, volatile solvents can freeze the morphology in a short time, and a more rigid conformation with strong intermolecular interaction combined with the solubility limit of PTzBI‐Si and N2200 in MTHF results in the formation of a fibril network in the bulk heterojunction. The multilength scaled morphology ensures fast transfer of carriers and facilitates exciton separation, which boosts carrier mobility and current density, thus improving the device performance. These results are of great significance for large‐scale printing fabrication of high‐efficiency all‐PSCs in the future.

A general approach for lab‐to‐manufacturing translation is developed to achieve high‐performance flexible organic solar modules without obvious efficiency loss. The shear impulse during the coating/printing process is applied to control the morphology evolution of the bulk heterojunction layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected.

Abstract

The blossoming of organic solar cells (OSCs) has triggered enormous commercial applications, due to their high‐efficiency, light weight, and flexibility. However, the lab‐to‐manufacturing translation of the praisable performance from lab‐scale devices to industrial‐scale modules is still the Achilles' heel of OSCs. In fact, it is urgent to explore the mechanism of morphological evolution in the bulk heterojunction (BHJ) with different coating/printing methods. Here, a general approach to upscale flexible organic photovoltaics to module scale without obvious efficiency loss is demonstrated. The shear impulse during the coating/printing process is first applied to control the morphology evolution of the BHJ layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected. Compelling results of morphological evolution, molecular stacking, and coarse‐grained molecular simulation verify the validity of the impulse translation. Accordingly, the efficiency of flexible devices via slot‐die printing achieves 9.10% for PTB7‐Th:PC₇₁BM and 9.77% for PBDB‐T:ITIC based on 1.04 cm² . Furthermore, 15 cm² flexible modules with effective efficiency up to 7.58% (PTB7‐Th:PC₇₁BM) and 8.90% (PBDB‐T:ITIC) are demonstrated with satisfying mechanical flexibility and operating stability. More importantly, this work outlines the shear impulse translation for organic printing electronics.

Photocurrent–voltage hysteresis in perovskite solar cells (PSCs) induced by ion migration combined with nonradiative recombination near the interface depends on perovskite composition and device structure. Among the methods used in the attempt to reduce the hysteresis, potassium‐ion doping is found to be a universal approach toward hysteresis‐free PSCs regardless of perovskite composition.

Abstract

Current‐density–voltage (J–V) hysteresis in perovskite solar cells (PSCs) is a critical issue because it is related to power conversion efficiency and stability. Although parameters affecting the hysteresis have been already reported and reviewed, little investigation is reported on scan‐direction‐dependent J–V curves depending on perovskite composition. This review investigates J–V hysteric behaviors depending on perovskite composition in normal mesoscopic and planar structure. In addition, methodologies toward hysteresis‐free PSCs are proposed. There is a specific trend in hysteresis in terms of J–V curve shape depending on composition. Ion migration combined with nonradiative recombination near interfaces plays a critical role in generating hysteresis. Interfacial engineering is found to be an effective method to reduce the hysteresis; however, bulk defect engineering is the most promising method to remove the hysteresis. Among the studied methods, KI doping is proved to be a universal approach toward hysteresis‐free PSCs regardless of perovskite composition. It is proposed from the current studies that engineering of perovskite film near the electron transporting layer (ETL) and the hole transporting layer (HTL) is of vital importance for achieving hysteresis‐free PSCs and extremely high efficiency.

Hybrid halide perovskites and ferroelectric perovskites are two different classes of materials with analogies in their structure. Such analogies and state‐of‐the‐art technologies based on these materials are reviewed so that future multisource energy conversion devices (which are capable of utilizing piezoelectric, pyroelectric, photovoltaic, and thermoelectric effects simultaneously) and storage devices can be created in a holistic manner.

Abstract

An insight into the analogies, state‐of‐the‐art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic–organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high‐efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo‐, pyro‐, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

A novel method is developed for fabricating high‐quality Ruddlesden–Popper perovskite films by directly using commercially available organic amines, avoiding extra chemical synthesis processing of organic ammonium halides. This new approach results in similar (and even better) device performance for both solar cells and light‐emitting diodes when compared with control devices fabricated from organic ammonium halides.

Abstract

Ruddlesden–Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, have emerged as a promising alternative to 3D perovskites for both photovoltaic and light‐emitting applications. The organic spacer layers provide a wide range of new possibilities to tune the properties and even provide new functionalities for RPPs. However, the preparation of state‐of‐the‐art RPPs requires organic ammonium halides as the starting materials, which need to be ex situ synthesized. A novel approach to prepare high‐quality RPP films through in situ formation of organic spacer cations from amines is presented. Compared with control devices fabricated from organic ammonium halides, this new approach results in similar (and even better) device performance for both solar cells and light‐emitting diodes. High‐quality RPP films are fabricated based on different types of amines, demonstrating the universality of the approach. This approach not only represents a new pathway to fabricate efficient devices based on RPPs, but also provides an effective method to screen new organic spacers with further improved performance.

A fullerene derivative, [6,6]‐phenyl‐C₆₁‐butyric acid‐N,N‐dimethyl‐3‐(2‐thienyl)propanam ester (PCBB‐S‐N), is designed and synthesized to correct defects in electron‐transporting layers (ETLs) and perovskite films. Its use leads to a promising power conversion efficiency (PCE) of 21.08% for perovskite solar cells. Importantly, devices containing PCBB‐S‐N simultaneously realize excellent thermal stability and water resistance.

Abstract

The poor long‐term stability of organic–inorganic hybrid halide perovskite solar cells (pero‐SCs) remains a big challenge for their commercialization. Although strategies such as encapsulation, doping, and passivation have been reported, there remains a lack of understanding of the water resistance and thermal stability of pero‐SCs. A fullerene derivative, [6,6]‐phenyl‐C₆₁‐butyric acid‐N,N‐dimethyl‐3‐(2‐thienyl)propanam ester (PCBB‐S‐N) containing a functional sulfur atom and C_60, is synthesized and employed as electron transporting layer (ETL)/intermediary layer to targetedly heal the multitype defects in pero‐SCs or assist the growth of ETL, such as [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), in planar p‐i‐n pero‐SCs. The repaired pero‐SCs can not only dramatically improve their power conversion efficiencies, but also address stability issues under moisture and high temperature. The corresponding mechanism of PCBB‐S‐N with targeted therapy effect in a device is systematically investigated by both experiments and theoretical calculation. This work demonstrates that the proposed fullerene derivative with finely tuned chemical structure can be a promising ETL candidate or intermediary to approach stable and efficient planar p‐i‐n pero‐SCs.

Herein, a facile strategy that can carry out double passivation to improve the performance of perovskite solar cells (PSCs) is demonstrated. By using the dilute halide salt PEABr solution to treat the perovskite film, PbI₂ can precipitate from the perovskite. Both PEABr and PbI₂ can passivate the perovskite film; double passivation improves the performance of PSCs significantly.

Material passivation is essential to enhance the quality of perovskite materials and boost the performance of perovskite solar cells (PSCs). However, most of the previous reports only paid attention to improving the quality of perovskite films by adopting single passivation. Here, a facile strategy that can carry out double passivation to improve the performance of PSCs is demonstrated. By using the dilute halide salt PEABr solution to treat the perovskite film, PbI₂ can precipitate from the perovskite. Both PEABr and PbI₂ can passivate the perovskite film, and by combining PEABr and PbI₂, the double passivation improves the performance of PSCs significantly. Very high short‐circuit current density of 24.30 mA cm⁻², open‐circuit voltage of 1.10 V, and fill factor of 79.75% are achieved which lead to a surprising efficiency of 21.32% for the passivated device. The improved efficiency is mainly according to the available surface passivation of the perovskite material, leading to repressed nonradiative recombination and unhindered charge collection. In addition, the passivated device exhibits better power conversion efficiency stability relative to the control device.

Publication date: November 2019

Source: Nano Energy, Volume 65

Author(s): Van-Dang Tran, S.V.N. Pammi, Byeong-Ju Park, Yire Han, Cheolho Jeon, Soon-Gil Yoon

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Publication date: November 2019

Source: Nano Energy, Volume 65

Author(s): Peng Zhai, Tzu-Sen Su, Tsung-Yu Hsieh, Wei-Yen Wang, Lixia Ren, Jiayi Guo, Tzu-Chien Wei

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