Zidan Liu

Nature Materials, Published online: 09 September 2019; doi:10.1038/s41563-019-0478-1

Addition of MXenes in the halide perovskite film, in the electron transport layer and at the interface between these layers is shown to enhance the efficiency of and reduce hysteresis in perovskite solar cells.

Nature Materials, Published online: 16 September 2019; doi:10.1038/s41563-019-0481-6

Reply to: On the ferroelectricity of CH₃NH₃PbI₃ perovskites

Nature Materials, Published online: 16 September 2019; doi:10.1038/s41563-019-0479-0

An investigation on Lewis acids reveals a mechanism for p-type doping of semiconducting polymers based on the formation of water–Lewis acid complexes, protonation of the polymer and electron transfer between neutral and charged chain segments.

Organic light‐emitting diodes (OLEDs) are used as light source for fluorescence microscopy. Spectral multiplexing enables high contrast and results in fluorescence images of live cells with similar image quality to conventional illumination. Furthermore, the device is applied to recording neuronal activity in small‐animal models at video rates.

Abstract

Fluorescence imaging is an indispensable tool in biology, with applications ranging from single‐cell to whole‐animal studies and with live mapping of neuronal activity currently receiving particular attention. To enable fluorescence imaging at cellular scale in freely moving animals, miniaturized microscopes and lensless imagers are developed that can be implanted in a minimally invasive fashion; but the rigidity, size, and potential toxicity of the involved light sources remain a challenge. Here, narrowband organic light‐emitting diodes (OLEDs) are developed and used for fluorescence imaging of live cells and for mapping of neuronal activity in Drosophila melanogaster via genetically encoded Ca²⁺ indicators. In order to avoid spectral overlap with fluorescence from the sample, distributed Bragg reflectors are integrated onto the OLEDs to block their long‐wavelength emission tail, which enables an image contrast comparable to conventional, much bulkier mercury light sources. As OLEDs can be fabricated on mechanically flexible substrates and structured into arrays of cell‐sized pixels, this work opens a new pathway for the development of implantable light sources that enable functional imaging and sensing in freely moving animals.

The changes in photophysical properties of mixed‐halide perovskite films under solar‐equivalent illumination are studied. The illumination generates localized low‐bandgap surface domains, onto which photoexcited charge carriers transfer and recombine with high radiative efficiency. The fraction of radiative and nonradiative (Auger) recombination bandgap can be balanced to achieve extremely high photoluminescence quantum yields at low excitation densities.

Abstract

Mixed‐halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution‐processed triple‐cation mixed‐halide (Cs_0.06MA_0.15FA_0.79)Pb(Br_0.4I_0.6)₃ perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar‐equivalent illumination. It is found that the illumination leads to localized surface sites of iodide‐rich perovskite intermixed with passivating PbI₂ material. Time‐ and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide‐rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed‐halide mixed‐cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.

Light‐emitting diodes constructed from biodegradable materials—ZnO as a direct bandgap semiconductor and Mo as semitransparent ultrathin electrodes—convert electrical power into light, in a platform that dissolves completely in aqueous solutions to biologically and environmentally benign end products. Such systems pave the way toward applications that cannot be addressed with conventional optoelectronic technologies, such as temporary medical implants and environmentally friendly displays.

Abstract

Transient forms of electronics, systems that disintegrate, dissolve, resorb, or sublime in a controlled manner after a well‐defined operating lifetime, are of interest for applications in hardware secure technologies, temporary biomedical implants, “green” consumer devices and other areas that cannot be addressed with conventional approaches. Broad sets of materials now exist for a range of transient electronic components, including transistors, diodes, antennas, sensors, and even batteries. This work reports the first examples of transient light‐emitting diodes (LEDs) that can completely dissolve in aqueous solutions to biologically and environmentally benign end products. Thin films of highly textured ZnO and polycrystalline Mo serve as semiconductors for light generation and conductors for transparent electrodes, respectively. The emitted light spans a range of visible wavelengths, where nanomembranes of monocrystalline silicon can serve as transient filters to yield red, green, and blue LEDs. Detailed characterization of the material chemistries and morphologies of the constituent layers, assessments of their performance properties, and studies of their dissolution processes define the underlying aspects. These results establish an electroluminescent light source technology for unique classes of optoelectronic systems that vanish into benign forms when exposed to aqueous conditions in the environment or in living organisms.

Organic photovoltaic (OPV) cells promise to have a good photovoltaic performance under the indoor light environment. Via optimizing the active layers, 1 cm² OPV cells are fabricated and a top power conversion efficiency of 22% under 1000 lux illumination is demonstrated.

Abstract

Organic photovoltaic (OPV) technologies have the advantages of fabricating larger‐area and light‐weight solar panels on flexible substrates by low‐cost roll‐to‐toll production. Recently, OPV cells have achieved many significant advances with power conversion efficiency (PCE) increasing rapidly. However, large‐scale solar farms using OPV modules still face great challenges, such as device stability. Herein, the applications of OPV cells in indoor light environments are studied. Via optimizing the active layers to have a good match with the indoor light source, 1 cm² OPV cells are fabricated and a top PCE of 22% under 1000 lux light‐emitting diode (2700 K) illumination is demonstrated. In this work, the light intensities are measured carefully. Incorporated with the external quantum efficiency and photon flux spectrum, the integral current densities of the cells are calculated to confirm the reliability of the photovoltaic measurement. In addition, the devices show much better stability under continuous indoor light illumination. The results suggest that designing wide‐bandgap active materials to meet the requirements for the indoor OPV cells has a great potential in achieving higher photovoltaic performance.

Efficient electron injection into organic semiconductors is achieved by hydrogen bond formation between the host materials and bases that are commonly used in organic synthesis as catalysts. The electron‐injection efficiency in inverted organic light‐emitting diodes, the electron‐injection layer of which consists of the host and bases, is found to be almost proportional to the basicity of the bases.

Abstract

Molecular n‐dopants that can lower the electron injection barrier between organic semiconductors and electrodes are essential in present‐day organic electronics. However, the development of stable molecular n‐dopants remains difficult owing to their low ionization potential, which generally renders them unstable. It is shown that the stable bases widely used in organic synthesis as catalysts can lower the electron injection barrier similar to that in conventional n‐doping in organic optoelectronic devices. In contrast to conventional n‐doping, which is based on the electron transfer from dopants with low ionization potential, the reduction of the injection barrier caused by adding bases is determined by the formation of hydrogen bonds between the hosts and the bases, providing energy‐level‐independent electron injection. The observation of the efficient electron injection induced by hydrogen bonding affords new perspectives on the method for controlling the behavior of electrons unique to organic semiconductors.

The variation of A‐site cations is promising to achieve enhanced properties; however, it is limited to a few available choices of methylamine, formamidine, and cesium. Halogenated methylammoniums are reported as novel A cations to broaden the family of hybrid perovskites, which breaks through the limitation of A cations.

Abstract

3D perovskites with typical structure of ABX₃ are emerging as key materials to achieve high‐performance optoelectronic devices. The variation of A‐site cation is promising to achieve enhanced properties; however, is limited to a few available choices of methylamine, formamidine, and cesium. In this work, halogenated‐methylammoniums are developed as A cation to broaden the family of hybrid perovskites. Single crystals and colloidal nanocrystals of halogenated‐methylammoniums based perovskites are successfully synthesized, showing bright future as alternatives for device exploration. In particular, the improved thermal stability and low exciton binding energy from single crystals measurements are demonstrated and bright tunable emission from blue to green for colloidal nanocrystals is achieved.

A novel red thermally activated delayed fluorescence (TADF) emitter, TPA–PZCN, is designed and synthesized. It simultaneously possesses a high Φ _PL of 97% and a small ΔE _ST of 0.13 eV. Red, deep‐red, and near‐infrared organic light‐emitting diodes (LEDs) based on it achieve record external quantum efficiencies of 27.4%, 28.1%, and 5.3%, respectively, which are the best performances in comparison with LEDs having a similar device structure.

Abstract

Researchers have spared no effort to design new thermally activated delayed fluorescence (TADF) emitters for high‐efficiency organic light‐emitting diodes (OLEDs). However, efficient long‐wavelength TADF emitters are rarely reported. Herein, a red TADF emitter, TPA–PZCN, is reported, which possesses a high photoluminescence quantum yield (Φ _PL) of 97% and a small singlet–triplet splitting (ΔE _ST) of 0.13 eV. Based on the superior properties of TPA–PZCN, red, deep‐red, and near‐infrared (NIR) OLEDs are fabricated by utilizing different device structure strategies. The red devices obtain a remarkable maximum external quantum efficiency (EQE) of 27.4% and an electroluminescence (EL) peak at 628 nm with Commission Internationale de L'Eclairage (CIE) coordinates of (0.65, 0.35), which represents the best result with a peak wavelength longer than 600 nm among those of the reported red TADF devices. Furthermore, an exciplex‐forming cohost strategy is adopted. The devices achieve a record EQE of 28.1% and a deep‐red EL peak at 648 nm with the CIE coordinates of (0.66, 0.34). Last, nondoped devices exhibit 5.3% EQE and an NIR EL peak at 680 nm with the CIE coordinates of (0.69, 0.30).

The OH…I⁻ hydrogen bonding interactions between poly(vinyl alcohol) (PVA) and FASnI₃ have the effects of introducing nucleation sites, slowing down crystal growth, directing the crystal orientation, reducing the trap states, and suppressing the migration of the ions. By adding PVA, the FASnI₃–PVA perovskite solar cells attain improved power conversion efficiency and stability.

Abstract

Tin‐based perovskites with narrow bandgaps and high charge‐carrier mobilities are promising candidates for the preparation of efficient lead‐free perovskite solar cells (PSCs). However, the crystalline rate of tin‐based perovskites is much faster, leading to abundant trap states and much lower open‐circuit voltage (V _oc). Here, hydrogen bonding is introduced to retard the crystalline rate of the FASnI₃ perovskite. By adding poly(vinyl alcohol) (PVA), the OH…I⁻ hydrogen bonding interactions between PVA and FASnI₃ have the effects of introducing nucleation sites, slowing down the crystal growth, directing the crystal orientation, reducing the trap states, and suppressing the migration of the iodide ions. In the presence of the PVA additive, the FASnI₃–PVA PSCs attain higher power conversion efficiency of 8.9% under a reverse scan with significantly improved V _oc from 0.55 to 0.63 V, which is one of the highest V _oc values for FASnI₃‐based PSCs. More importantly, the FASnI₃–PVA PSCs exhibit striking long‐term stability, with no decay in efficiency after 400 h of operation at the maximum power point. This approach, which makes use of the OH…I⁻ hydrogen bonding interactions between PVA and FASnI₃, is generally applicable for improving the efficiency and stability of the FASnI₃‐based PSCs.

By rationally tuning the molecular interaction and energy level alignments of the donors and acceptors, when both donor and acceptor are fluorinated or both are not fluorinated, high‐performance organic photovoltaics can be realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, devices based on the PBDB‐T‐F/Y1‐4F blend and PBDB‐T‐F/Y6 exhibit power conversion efficiencies as high as 14.8% and 15.9%, respectively.

Abstract

The performance of organic photovoltaics (OPVs) has rapidly improved over the past years. Recent work in material design has primarily focused on developing near‐infrared nonfullerene acceptors with broadening absorption that pair with commercialized donor polymers; in the meanwhile, the influence of the morphology of the blend film and the energy level alignment on the efficiency of charge separation needs to be synthetically considered. Herein, the selection rule of the donor/acceptor blend is demonstrated by rationally considering the molecular interaction and energy level alignment, and highly efficient OPV devices using both‐fluorinated or both‐nonfluorinated donor/acceptor blends are realized. With the enlarged absorption, ideal morphology, and efficient charge transfer, the devices based on the PBDB‐T‐F/Y1‐4F blend and PBDB‐T‐F/Y6 exhibit champion power conversion efficiencies as high as 14.8% and 15.9%, respectively.

Publication date: November 2019

Source: Solar Energy Materials and Solar Cells, Volume 202

Author(s): Yi-Ming Chang, Chuang-Yi Liao, Chun-Chieh Lee, Shang-Yi Lin, Nai-Wei Teng, Phoebe Huei-Shuan Tan

Graphical abstract

Publication date: November 2019

Source: Solar Energy Materials and Solar Cells, Volume 202

Author(s): Rico Meitzner, Tobias Faber, Shahidul Alam, Aman Amand, Roland Roesch, Mathias Büttner, Felix Herrmann-Westendorf, Martin Presselt, Laura Ciammaruchi, Iris Visoly-Fisher, Sjoerd Veenstra, Amaia Diaz de Zerio, Xiaofeng Xu, Ergang Wang, Christian Müller, Pavel Troshin, Martin D. Hager, Sandra Köhn, Michal Dusza, Miron Krassas

Application of the proposed slow post‐annealing for layered 2D perovskite solar cells based on BA₂MA₃Pb₄I₁₃ photo‐absorber leads to a favorable alignment on the multi‐perovskite phases and resultant champion power conversion efficiency to 17.26%, showing simultaneously enhanced open‐circuit voltage and short‐circuit current.

Abstract

Layered Ruddlesden–Popper (RP) phase (2D) halide perovskites have attracted tremendous attention due to the wide tunability on their optoelectronic properties and excellent robustness in photovoltaic devices. However, charge extraction/transport and ultimate power conversion efficiency (PCE) in 2D perovskite solar cells (PSCs) are still limited by the non‐eliminable quantum well effect. Here, a slow post‐annealing (SPA) process is proposed for BA₂MA₃Pb₄I₁₃ (n = 4) 2D PSCs by which a champion PCE of 17.26% is achieved with simultaneously enhanced open‐circuit voltage, short‐circuit current, and fill factor. Investigation with optical spectroscopy coupled with structural analyses indicates that enhanced crystal orientation and favorable alignment on the multiple perovskite phases (from the 2D phase near bottom to quasi‐3D phase near top regions) is obtained with SPA treatment, which promotes carrier transport/extraction and suppresses Shockley–Read–Hall charge recombination in the solar cell. As far as it is known, the reported PCE is so far the highest efficiency in RP phase 2D PSCs based on butylamine (BA) spacers (n = 4). The SPA‐processed devices exhibit a satisfactory stability with <4.5% degradation after 2000 h under N₂ environment without encapsulation. The demonstrated process strategy offers a promising route to push forward the performance in 2D PSCs toward realistic photovoltaic applications.

Recent progress of inorganic perovskite materials and photovoltaic solar cells is summarized, including materials design, methods for preparing high‐quality perovskite films, phase instabilities, nanocrystals, quantum dots, lead‐free perovskites, device process, and upscaling. In addition, the energy loss mechanisms within the device are discussed and relevant methods are proposed accordingly.

Abstract

All‐inorganic perovskites are considered to be one of the most appealing research hotspots in the field of perovskite photovoltaics in the past 3 years due to their superior thermal stability compared to their organic–inorganic hybrid counterparts. The power‐conversion efficiency has reached 17.06% and the number of important publications is ever increasing. Here, the progress of inorganic perovskites is systematically highlighted, covering materials design, preparation of high‐quality perovskite films, and avoidance of phase instabilities. Inorganic perovskites, nanocrystals, quantum dots, and lead‐free compounds are discussed and the corresponding device performances are reviewed, which have been realized on both rigid and flexible substrates. Methods for stabilization of the cubic phase of low‐bandgap inorganic perovskites are emphasized, which is a prerequisite for highly efficient and stable solar cells. In addition, energy loss mechanisms both in the bulk of the perovskite and at the interfaces of perovskite and charge selective layers are unraveled. Reported approaches to reduce these charge‐carrier recombination losses are summarized and complemented by methods proposed from our side. Finally, the potential of inorganic perovskites as stable absorbers is assessed, which opens up new perspectives toward the commercialization of inorganic perovskite solar cells.

Publication date: November 2019

Source: Solar Energy Materials and Solar Cells, Volume 202

Author(s): Zhengyang Gao, Ge Yan, Mingliang Zhao, Shaopeng Xu, Linlin Li, Hanyu Huang, Weijie Yang, Xunlei Ding

Nature, Published online: 27 August 2019; doi:10.1038/d41586-019-02555-y

For a fortunate group, exercise and the right diet could protect against cognitive symptoms that develop with age.

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.

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.

Technologies to enhance the stability of quantum dots (QDs), quantum dot films, and quantum dot light‐emitting diodes for display applications are summarized and suggested. Degradation mechanisms of QDs are discussed in aspects of water, oxygen, and thermal energy. Various technologies to maintain the quantum yield of QDs, the photoluminescence intensity of QD films, and the lifetime of quantum dot light‐emitting diodes are discussed.

Abstract

Quantum dots (QDs) are being highlighted in display applications for their excellent optical properties, including tunable bandgaps, narrow emission bandwidth, and high efficiency. However, issues with their stability must be overcome to achieve the next level of development. QDs are utilized in display applications for their photoluminescence (PL) and electroluminescence. The PL characteristics of QDs are applied to display or lighting applications in the form of color‐conversion QD films, and the electroluminescence of QDs is utilized in quantum dot light‐emitting diodes (QLEDs). Studies on the stability of QDs and QD devices in display applications are reviewed herein. QDs can be degraded by oxygen, water, thermal heating, and UV exposure. Various approaches have been developed to protect QDs from degradation by controlling the composition of their shells and ligands. Phosphorescent QDs have been protected by bulky ligands, physical incorporation in polymer matrices, and covalent bonding with polymer matrices. The stability of electroluminescent QLEDs can be enhanced by using inorganic charge transport layers and by improving charge balance. As understanding of the degradation mechanisms of QDs increases and more stable QDs and display devices are developed, QDs are expected to play critical roles in advanced display applications.

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.

In article number https://doi.org/10.1002/adma.2019024311902431, Bo Tian, Weiwei Cai, Xixiang Zhang, and co‐workers reveal the existence of a fractal‐growth‐based mechanism in 2D‐material chemical vapor deposition (CVD) syntheses. Based on a 2D diffusion‐limited aggregation model, perfect correlations between theoretically simulated data and CVD experimental results are obtained. Eventually, the precise control of 2D‐material shapes and qualities is achieved by adjusting single‐domain net growth rates in the CVD‐growth process.

In article number https://doi.org/10.1002/adma.2019019661901966, Guichuan Xing, Yanlin Song, and co‐workers present a new low‐dimensional perovskite based on 1,4‐butanediamine (BEA), with the alternating ordered of diammonium and monoammonium cations in the interlayer space. Taking advantage of the short layer spacing and hydrogen bonding, a barrier‐free and balanced carrier‐transport pathway with an enhanced carrier‐diffusion mechanism is proposed. Due to the hydrophobicity of BEA, the new low‐dimensional perovskite exhibits excellent stability.

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 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.

Publication date: November 2019

Source: Solar Energy Materials and Solar Cells, Volume 202

Author(s): Rahul Ranjan, Belal Usmani, Sudhir Ranjan, Hasitha C. Weerasinghe, Anand Singh, Ashish Garg, Raju Kumar Gupta

Graphical abstract

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.