Two-step thermal annealing improves the morphology of spin-coated films for highly efficient perovskite hybrid photovoltaics

High-Throughput Roll-to-Roll Processed Large-Area Perovskite Solar Cells Using Rapid Radiation Annealing Technique

The development of a stable roll-to-roll (R2R) process for flexible large-area perovskite solar cells (PSCs) and modules is a pressing challenge. In this study, we introduced a new R2R PSC manufacturing system that employs a two-step deposition method for coating perovskite and uses intensive pulsed light (IPL) for annealing. This system has successfully fabricated small-sized cells and the first-ever large-sized, R2R-processed flexible modules. A key focus of our work was to accelerate the conversion of PbI2 to perovskite. To this end, we utilized IPL annealing and incorporated additives into the PbI2 layer. With these modifications, the R2R-processed perovskite films achieved a power conversion efficiency (PCE) of 16.87%, representing the highest reported value for R2R two-step processed PSCs. However, these cells exhibited hysteresis in reverse and forward PCE measurements. To address this, we introduced a dual-annealing process consisting of IPL followed by a 2-min thermal heating step. This approach successfully reduced hysteresis, resulting in low-hysteresis, R2R-processed flexible PSCs. Moreover, we fabricated large-scale flexible modules (10 × 10 cm2) with a PCE of 11.25% using the dual-annealing system, marking a significant milestone in this field.

Highly Stable and Enhanced Performance of p-i-n Perovskite Solar Cells via Cuprous Oxide Hole-Transport Layers

Solar light is a renewable source of energy that can be used and transformed into electricity using clean energy technology. In this study, we used direct current magnetron sputtering (DCMS) to sputter p-type cuprous oxide (Cu₂O) films with different oxygen flow rates (f_O2) as hole-transport layers (HTLs) for perovskite solar cells (PSCs). The PSC device with the structure of ITO/Cu₂O/perovskite/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM)/bathocuproine (BCP)/Ag showed a power conversion efficiency (PCE) of 7.91%. Subsequently, a high-power impulse magnetron sputtering (HiPIMS) Cu₂O film was embedded and promoted the device performance to 10.29%. As HiPIMS has a high ionization rate, it can create higher density films with low surface roughness, which passivates surface/interface defects and reduces the leakage current of PSCs. We further applied the superimposed high-power impulse magnetron sputtering (superimposed HiPIMS) derived Cu₂O as the HTL, and we observed PCEs of 15.20% under one sun (AM1.5G, 1000 Wm^-2) and 25.09% under indoor illumination (TL-84, 1000 lux). In addition, this PSC device outperformed by demonstrating remarkable long-term stability via retaining 97.6% (dark, Ar) of its performance for over 2000 h.

Recent progress in hybrid perovskite solar cells through scanning tunneling microscopy and spectroscopy

Currently, sustainable renewable energy sources are urgently required to fulfill the cumulative energy needs of the world's 7.8 billion population, since the conventional coal and fossil fuels will be exhausted soon. Photovoltaic devices are a direct and efficient means to produce a huge amount of energy to meet these energy targets. In particular, hybrid-perovskite-based photovoltaic devices merit special attention not only due to their exceptional efficiency for generating appreciable energy but also their tunable band gaps and the ease of device fabrication. However, the commercialization of such devices suffers from the instability of the compositional materials. The cause of instability is the perovskite's structure and its morphology at the sub-molecular level; thereby revealing and eliminating these instabilities are a striking challenge. To address this issue, scanning tunneling microscopy/spectroscopy (STM/STS) presents a comprehensive method to allow the visualization of the morphology and electronic structure of materials at atomic-level resolution. Here, we review the recent developments of perovskite-based solar cells (PSCs), the STM/STS analysis of photoactive halide/hybrid and oxide materials, and the real-time STM/STS investigation of electronic structures with defects and traps that are believed to mainly affect device performances. The detailed STM/STS analysis can facilitate a better understanding of the properties of materials at the nanoscale. This informative study may hold great promise to advance the development of stable PSCs under atmospheric conditions.

Synaptic plasticity, metaplasticity and memory effects in hybrid organic-inorganic bismuth-based materials

Since the discovery of memristors, their application in computing systems utilizing multivalued logic and a neuromimetic approach is of great interest. A thin film device made of methylammonium bismuth iodide exhibits a wide variety of neuromorphic effects simultaneously, and is thus able to mimic synaptic behaviour and learning phenomena. Standard learning protocols, such as spike-timing dependent plasticity and spike-rate dependent plasticity might be further modulated via metaplasticity in order to amplify or alter changes in the synaptic weight. Moreover, transfer of information from short-term to long-term memory is observed. These effects show that the diversity of functions of memristive devices can be strongly affected by the pre-treatment of the sample. Modulation of the resistive switching amplitude is of great importance for the application of memristive elements in computational applications, as additional sub-states might be utilized in multi-valued logic systems and metaplasticity and memory consolidation will contribute to the development of more efficient bioinspired computational schemes.

Improving the performance of lead acetate-based perovskite solar cells via solvent vapor annealing

The perovskite layers with large grain size and less pinhole were achieved by adding DMF during the thermal annealing process.

Electronic and optical properties of perovskite compounds MA1−αFAαPbI3−βXβ (X = Cl, Br) explored for photovoltaic applications

As outstanding light harvesters, solution-processable organic–inorganic hybrid perovskites (OIHPs) have been drawing considerable attention thanks to their higher power conversion efficiency (PCE) and cost-effective synthesis relative to other photovoltaic materials. Nevertheless, their further development is severely hindered by the drawbacks of poor stability and rapid degradation in particular. First-principles calculations based on density functional theory (DFT) are hence performed towards the perovskite compounds MA_1−αFA_αPbI_3−βX_β (X = Cl, Br), with the aim of exploring more efficient and stable OIHPs. In addition to that, a hybrid density functional is adopted for exact electronic properties, and their band structures indicate that the doped series are all direct band-gap semiconductors. Moreover, the defect formation energies indicate that the stability of perovskite compounds can be significantly enhanced via ion doping. Meanwhile, it is unveiled that the optical performance of the doped perovskite series is also effectively improved through ion doping. Therefore, the investigated perovskite compounds MA_1−αFA_αPbI_3−βX_β (X = Cl, Br) are promising candidates for enhancing solar-energy conversion efficiency. Our results pave a way in deeper understanding of the inherent characteristics of OIHPs, which is useful for designing new-type perovskite-based photovoltaic devices.

The absorption performance of perovskite CH₃NH₃PbI₃ can be significantly improved via mono-, or co-doping of organic cations and halide ions.

High-Performance Photodetectors Based on Solution-Processed Epitaxial Grown Hybrid Halide Perovskites

Hybrid organic-inorganic halide perovskites (HOIPs) have recently attracted tremendous attention because of their excellent semiconducting and optoelectronic properties, which exist despite their morphology and crystallinity being far inferior to those of more mature semiconductors, such as silicon and III-V compound semiconductors. Heteroepitaxy can provide a route to achieving high-performance HOIP devices when high crystalline quality and smooth morphology are required, but work on heteroepitaxial HOIPs has not previously been reported. Here, we demonstrate epitaxial growth of methylammonium lead iodide (MAPbI₃) on single crystal KCl substrates with smooth morphology and the highest carrier recombination lifetime (∼213 ns) yet reported for nonsingle crystalline MAPbI₃. Experimental Raman spectra agree well with theoretical calculations, presenting in particular a sharp peak at 290 cm^-1 for the torsional mode of the organic cations, a marker of orientational order and typically lacking in previous reports. Photodetectors were fabricated showing excellent performance, confirming the high quality of the epitaxial MAPbI₃ thin films. This work provides a new strategy to enhance the performance of all HOIPs-based devices.

All Sequential Dip-Coating Processed Perovskite Layers from an Aqueous Lead Precursor for High Efficiency Perovskite Solar Cells

A novel, sequential method of dip-coating a ZnO covered mesoporous TiO2 electrode was performed using a non-halide lead precursor in an aqueous system to form a nanoscale perovskite film. The introduction of a ZnO interfacial layer induced significant adsorption in the non-halide lead precursor system. An efficient successive solid-state ion exchange and reaction process improved the morphology, crystallinity, and stability of perovskite solar cells. Improved surface coverage was achieved using successive ionic layer adsorption and reaction processes. When all sequential dipping conditions were controlled, a notable power conversion efficiency of 12.41% under standard conditions (AM 1.5, 100 mW·cm-2) was achieved for the perovskite solar cells fabricated from an aqueous non-halide lead precursor solution without spin-casting, which is an environmentally benign and low-cost manufacturing processes.

Temperature Gradient-Induced Instability of Perovskite via Ion Transport

Perovskite has been known as a promising novel material for photovoltaics and other fields because of its excellent opto-electric properties and convenient fabrication. However, its stability has been a widely known haunting factor that has severely deteriorated its application in reality. In this work, it has been discovered for the first time that perovskite can become significantly chemically unstable with the existence of a temperature gradient in the system, even at temperature far below its thermal decomposition condition. A study of the detailed mechanism has revealed that the existence of a temperature gradient could induce a mass transport process of extrinsic ionic species into the perovskite layer, which enhances its decomposition process. Moreover, this instability could be effectively suppressed with a reduced temperature gradient by simple structural modification of the device. Further experiments have proved the existence of this phenomenon in different perovskites with various mainstream substrates, indicating the universality of this phenomenon in many previous studies and future research. Hopefully, this work may bring deeper understanding of its formation mechanisms and facilitate the general development of perovskite toward its real application.

The role of a vapor-assisted solution process on tailoring the chemical composition and morphology of mixed-halide perovskite solar cells

Herein, we report a modified two-step method to construct a uniform and pinhole-free polycrystalline perovskite film with large grains up to the microscale using lead mixed-halide (PbI₂–PbCl₂) precursor solutions to guarantee the device functioning.

Low-temperature, simple and efficient preparation of perovskite solar cells using Lewis bases urea and thiourea as additives: stimulating large grain growth and providing a PCE up to 18.8%

We demonstrated that urea can be used as an efficient additive for perovskite solar cells with a remarkable performance of 18.8%.

Enhancing the Performance of Perovskite Solar Cells by Hybridizing SnS Quantum Dots with CH3 NH3 PbI3

The combination of perovskite solar cells and quantum dot solar cells has significant potential due to the complementary nature of the two constituent materials. In this study, solar cells (SCs) with a hybrid CH₃ NH₃ PbI₃ /SnS quantum dots (QDs) absorber layer are fabricated by a facile and universal in situ crystallization method, enabling easy embedding of the QDs in perovskite layer. Compared with SCs based on CH₃ NH₃ PbI₃ , SCs using CH₃ NH₃ PbI₃ /SnS QDs hybrid films as absorber achieves a 25% enhancement in efficiency, giving rise to an efficiency of 16.8%. The performance improvement can be attributed to the improved crystallinity of the absorber, enhanced photo-induced carriers' separation and transport within the absorber layer, and improved incident light utilization. The generality of the methods used in this work paves a universal pathway for preparing other perovskite/QDs hybrid materials and the synthesis of entire nontoxic perovskite/QDs hybrid structure.

Morphology Engineering: A Route to Highly Reproducible and High Efficiency Perovskite Solar Cells

Despite the rapid increase in the performance of perovskite solar cells (PSC), they still suffer from low lab-to-lab or people-to-people reproducibility. Aiming for a universal condition to high-performance devices, we investigated the morphology evolution of a composite perovskite by tuning annealing temperature and precursor concentration of the perovskite film. Here, we introduce thermal annealing as a powerful tool to generate a well-controlled excess of PbI₂ in the perovskite formulation and show that this benefits the photovoltaic performance. We demonstrated the correlation between the film microstructure and electronic property and device performance. An optimized average grain size/thickness aspect ratio of the perovskite crystallite is identified, which brings about a highly reproducible power conversion efficiency (PCE) of 19.5 %, with a certified value of 19.08 %. Negligible hysteresis and outstanding morphology stability are observed with these devices. These findings lay the foundation for further boosting the PCE of PSC and can be very instructive for fabrication of high-quality perovskite films for a variety of applications, such as light-emitting diodes, field-effect transistors, and photodetectors.

Structure-Property Relations of Methylamine Vapor Treated Hybrid Perovskite CH3NH3PbI3 Films and Solar Cells

The power conversion efficiency of halide perovskite solar cells is heavily dependent on the perovskite layer being sufficiently smooth and pinhole-free. It has been shown that these features can be obtained even when starting out from rough and discontinuous perovskite film by briefly exposing the film to methylamine (MA) vapor. The exact underlying physical mechanisms of this phenomenon are, however, still unclear. By investigating smooth, MA treated films based on very rough and discontinuous reference films of methylammonium triiode (MAPbI₃) and considering their morphology, crystalline features, local conductive properties, and charge carrier lifetime, we unraveled the relation between their characteristic physical qualities and their performance in corresponding solar cells. We discovered that the extensive improvement in photovoltaic performance upon MA treatment is a consequence of the induced morphological enhancement of the perovskite layer together with improved electron injection into TiO₂, which in fact compensates for an otherwise compromised bulk electronic quality simultaneously caused by the MA treatment.

Solution processed double-decked V2Ox/PEDOT:PSS film serves as the hole transport layer of an inverted planar perovskite solar cell with high performance

Solution processed double-decked V₂O_x/PEDOT:PSS HTL film can effectively improve optoelectronic properties of PSC devices.

Improving the stability of the perovskite solar cells by V2O5 modified transport layer film

A PSC with high lifetime was prepared by inserting V₂O₅ film between the ITO electrode and PEDOT:PSS HTL.

Effects of the additives n-propylammonium or n-butylammonium iodide on the performance of perovskite solar cells

The presence of C₃H₇NH₃I caused the perovskite films to grow with high coverage, thereby allowing the devices to display high performance.

Sonochemical synthesis of CH3NH3PbI3 perovskite ultrafine nanocrystal sensitizers for solar energy applications

The organic-inorganic hybrid perovskite CH3NH3PbI3 is becoming an interesting material in the field of energy harvesting. This material is one of the cleanest and cheapest components in solar cells which is available in ample amounts. However, most of the previous research work was done on thin film of this material. In the present work we describe the preparation of a powder containing nanoparticles of CH3NH3PbI3 using a sonochemical method. Characterization of the product was done by various methods, such as HRTEM, FTIR, PL, DLS and XRD. The particles were found to be highly crystalline (tetragonal crystal structure), polygonal in shape and having diameters of 10-40nm.

Towards Optimum Solution-processed Planar Heterojunction Perovskite Solar Cells

Recently, organic–inorganic hybrid perovskites have been proven to be excellent photovoltaic materials, exhibiting outstanding light absorption, high carrier mobility and facile solution processability. Besides the low-cost manufacturing of perovskite thin-films, the power conversion efficiencies demonstrated for this class of materials are already at the same level as those of poly-crystalline silicon. The pursuit of efficiency in the field of metal halide perovskite solar cells has been achieved mainly through the improvement to perovskite deposition processing and optimization of the contact materials. In this chapter, we review the commonly employed perovskite deposition techniques, with special emphasis on the morphological quality of the prepared perovskite films. Films which exhibit the largest grains and highest orientation also achieve the highest performance, as long as full surface coverage is ensured. Here, it is also important to tune the energy levels of the electron and hole acceptors, and several strategies have led to champion devices with open circuit voltages between 1.1 and 1.15 V for state-of-the-art systems. However, most of the organic materials used currently are synthesized using expensive cross-coupling reactions that require stringent reaction conditions and extensive product purification, so that they cannot be produced at a low-cost at present. For perovskite solar cells to be able to enter the photovoltaic market, their cost and stability need to be competitive with current established technologies. The development of new chemistries resulting in simple compound purification, such as those based on azomethine bonds, will be an essential part of future molecular design for perovskite solar cells.

High Performance Perovskite Solar Cells

Perovskite solar cells fabricated from organometal halide light harvesters have captured significant attention due to their tremendously low device costs as well as unprecedented rapid progress on power conversion efficiency (PCE). A certified PCE of 20.1% was achieved in late 2014 following the first study of long-term stable all-solid-state perovskite solar cell with a PCE of 9.7% in 2012, showing their promising potential towards future cost-effective and high performance solar cells. Here, notable achievements of primary device configuration involving perovskite layer, hole-transporting materials (HTMs) and electron-transporting materials (ETMs) are reviewed. Numerous strategies for enhancing photovoltaic parameters of perovskite solar cells, including morphology and crystallization control of perovskite layer, HTMs design and ETMs modifications are discussed in detail. In addition, perovskite solar cells outside of HTMs and ETMs are mentioned as well, providing guidelines for further simplification of device processing and hence cost reduction.

Credible evidence for the passivation effect of remnant PbI₂ in CH₃NHCH₃PbICH₃ films in improving the performance of perovskite solar cells

The role of remnant PbI2 in CH3NH3PbI3 films is still controversial, some investigations have revealed that the remnant PbI2 plays a passivation role, reduces the charge recombination in perovskite solar cells (PSCs), and improves the performance of PSCs, but the opposing views state that remnant PbI2 has no passivation effect and it would deteriorate the stability of the devices. In our investigation, the CH3NH3PbI3 films have been prepared by a two-step spin-coating method and the content of the remnant PbI2 in CH3NH3PbI3 films has been tuned by varying the preparation temperature. It has been found that increasing the heating temperature could increase the coverage of spin-coated PbI2 films, which has led to high coverage CH3NH3PbI3 films and more remnant PbI2 in CH3NH3PbI3 films, and as a result, the performance of PSCs was enhanced obviously and the maximum power conversion efficiency of 14.32 ± 0.28% was achieved by the PSCs prepared at 130/120 °C (PbI2 films were heated at 130 °C and CH3NH3PbI3 films were heated at 120 °C). Furthermore, the dark current, electrochemical impedance spectroscopy and time-resolved fluorescence emission decay measurements revealed that the charge recombination in PSCs has been gradually suppressed and the fluorescence emission lifetime has gradually increased with the content of remnant PbI2 increasing. Thus, the passivation effects of the unreacted and decomposed PbI2 in improving the performance of PSCs have been confirmed unquestionably.

Fast and Controllable Crystallization of Perovskite Films by Microwave Irradiation Process

The crystal growth process significantly influences the properties of organic-inorganic halide perovskite films along with the performance of solar cell devices. In this paper, we adopted the microwave irradiation to treat perovskite films through a one-step deposition method for several minutes at a fixed output power. It is found that the specific microwave irradiation process can evaporate the solvent directly and heat perovskite film quickly. In comparison with the conventional thermal annealing process, a microwave irradiation process assisted fast and controllable crystallization of perovskite films with less energy-loss and time-consumption and therefore resulted in the enhancement in the photovoltaic performance of the corresponding solar cells.

Crystal Structure Formation of CH₃NH₃PbI3-xClx Perovskite

Inorganic-organic hydride perovskites bring the hope for fabricating low-cost and large-scale solar cells. At the beginning of the research, two open questions were raised: the hysteresis effect and the role of chloride. The presence of chloride significantly improves the crystallization and charge transfer property of the perovskite. However, though the long held debate over of the existence of chloride in the perovskite seems to have now come to a conclusion, no prior work has been carried out focusing on the role of chloride on the electronic performance and the crystallization of the perovskite. Furthermore, current reports on the crystal structure of the perovskite are rather confusing. This article analyzes the role of chloride in CH₃NH₃PbI_3-xCl_x on the crystal orientation and provides a new explanation about the (110)-oriented growth of CH₃NH₃PbI₃ and CH₃NH₃PbI_3-xCl_x.

Photovoltaic Performance of Perovskite Solar Cells with Different Grain Sizes

Perovskite solar cells exhibit improved photovoltaic parameters with increasing perovskite grain size. The larger photocurrent is due to the enhanced absorption efficiency for thicker perovskite layers. The larger open-circuit voltage (VOC ) is ascribed to the reduced trap-assisted recombination for the larger grains. As a result, the power conversion efficiency exceeds 19% at best. Further improvement in VOC would be possible if the trap density were reduced.

Recent progress and challenges of organometal halide perovskite solar cells

We review recent progress in the development of organometal halide perovskite solar cells. We discuss different compounds used to construct perovskite photoactive layers, as well as the optoelectronic properties of this system. The factors that affect the morphology of the perovskite active layer are explored, e.g. material composition, film deposition methods, casting solvent and various post-treatments. Different strategies are reviewed that have recently emerged to prepare high performing perovskite films, creating polycrystalline films having either large or small grain size. Devices that are constructed using meso-superstructured and planar architectures are summarized and the impact of the fabrication process on operational efficiency is discussed. Finally, important research challenges (hysteresis, thermal and moisture instability, mechanical flexibility, as well as the development of lead-free materials) in the development of perovskite solar cells are outlined and their potential solutions are discussed.

Inverted thermal annealing of perovskite films: a method for enhancing photovoltaic device efficiency

A novel method called inverted thermal annealing was adopted to treat perovskite films for efficient PSCs.

Improved efficiency of solution-processed bulk-heterojunction organic solar cells and planar-heterojunction perovskite solar cells with efficient hole-extracting Si nanocrystals

Si nanocrystals for efficient hole extraction in solution-processed BHJ OSCs and PHJ PrSCs led highly enhanced PCEs by ~11% and ~23% respectively, compared with those without Si nanocrystals.

Evolution in surface coverage of CH3NH3PbI3−XClXvia heat assisted solvent vapour treatment and their effects on photovoltaic performance of devices

We demonstrate a facile and well controlled heat assisted solvent vapour treatment (HASVT) method for the growth of compact perovskite layers with good surface coverage areas in ambient atmosphere.

Revealing the unfavorable role of superfluous CH3NH3PbI3 grain boundary traps in perovskite solar cells on carrier collection

In this work, the perovskite films with controllable grain size are obtained by a facile method. And the unfavorable role of perovskite grain boundary traps is unveiled by the combination of experiment and simulation analysis.

Highly reproducible perovskite solar cells with excellent CH3NH3PbI3−xClx film morphology fabricated via high precursor concentration

A novel method was proposed to achieve excellent CH₃NH₃PbI_3−xClx films based on a high concentration spinning process, which offered an effective strategy for highly reproducible perovskite solar cells with excellent morphology.

Recent progress on stability issues of organic–inorganic hybrid lead perovskite-based solar cells

Over the past few years, substantial progress has been made in research on organic–inorganic halide perovskite solar cells.

Controlling CH3NH3PbI(3-x)Cl(x) Film Morphology with Two-Step Annealing Method for Efficient Hybrid Perovskite Solar Cells

The methylammonium lead halide perovskite solar cells have become very attractive because they can be prepared with low-cost solution-processable technology and their power conversion efficiency have been increasing from 3.9% to 20% in recent years. However, the high performance of perovskite photovoltaic devices are dependent on the complicated process to prepare compact perovskite films with large grain size. Herein, a new method is developed to achieve excellent CH3NH3PbI3-xClx film with fine morphology and crystallization based on one step deposition and two-step annealing process. This method include the spin coating deposition of the perovskite films with the precursor solution of PbI2, PbCl2, and CH3NH3I at the molar ratio 1:1:4 in dimethylformamide (DMF) and the post two-step annealing (TSA). The first annealing is achieved by solvent-induced process in DMF to promote migration and interdiffusion of the solvent-assisted precursor ions and molecules and realize large size grain growth. The second annealing is conducted by thermal-induced process to further improve morphology and crystallization of films. The compact perovskite films are successfully prepared with grain size up to 1.1 μm according to SEM observation. The PL decay lifetime, and the optic energy gap for the film with two-step annealing are 460 ns and 1.575 eV, respectively, while they are 307 and 327 ns and 1.577 and 1.582 eV for the films annealed in one-step thermal and one-step solvent process. On the basis of the TSA process, the photovoltaic devices exhibit the best efficiency of 14% under AM 1.5G irradiation (100 mW·cm(-2)).

Recent progress in efficient hybrid lead halide perovskite solar cells

The efficiency of perovskite solar cells (PSCs) has been improved from 9.7 to 19.3%, with the highest value of 20.1% achieved in 2014. Such a high photovoltaic performance can be attributed to optically high absorption characteristics and balanced charge transport properties with long diffusion lengths of the hybrid lead halide perovskite materials. In this review, some fundamental details of hybrid lead iodide perovskite materials, various fabrication techniques and device structures are described, aiming for a better understanding of these materials and thus highly efficient PSC devices. In addition, some advantages and open issues are discussed here to outline the prospects and challenges of using perovskites in commercial photovoltaic devices.

Improved hole interfacial layer for planar perovskite solar cells with efficiency exceeding 15%

Planar structure has been proven to be efficient and convenient in fabricating low-temperature and solution-processing perovkite solar cells (PSCs). Interface control and crystal film growth of organometal halide films are regarded as the most important factors to obtain high-performance PSCs. Herein, we report a solution-processed

PEDOT

PSS-GeO2 composite films by simply incorporating the GeO2 aqueous solution into the

PEDOT

PSS aqueous dispersion as a hole transport layer in planar PSCs. Besides the merits of high conductivity, ambient stability and interface modification of

PEDOT

PSS-GeO2 composite films, the formed island-like GeO2 particles are assumed to act as growing sites of crystal nucleus of perovskite films during annealing. By the seed-mediation of GeO2 particles, a superior CH3NH3PbI(3-x)Cl(x) crystalline film with large-scale domains and good film uniformity was obtained. The resulting PSC device with

PEDOT

PSS-GeO2 composite film as HTL shows a best performance with 15.15% PCE and a fill factor (FF) of 74%. There is a remarkable improvement (∼37%) in PCE, from 9.87% to 13.54% (in average for over 120 devices), compared with the reference pristine

PEDOT

PSS based device.

Inverted planar heterojunction perovskite solar cells employing polymer as the electron conductor

Inverted planar heterojunction perovskite solar cells employing different polymers, poly{[N,N'-bis(2-octyldodecyl)-1,4,5,8-naphthalene diimide-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (N2200), poly{[N,N'-bis(alkyl)-1,4,5,8-naphthalene diimide-2,6-diyl-alt-5,5'-di(thiophen-2-yl)-2,2'-(E)-2-(2-(thiophen-2-yl)vinyl)thiophene]} (PNVT-8), and PNDI2OD-TT as electron-transporting material (ETM) have been investigated for the first time. The best device performance was obtained when N2200 was applied as the ETM, with JSC of 14.70 mA/cm2, VOC of 0.84 V, and fill factor (FF) of 66%, corresponding to a decent power conversion efficiency (PCE) of ∼ 8.15%. Which is very competitive to the parameters (JSC 14.65 mA/cm2, VOC 0.83 V, FF 70%, and PCE 8.51%) of the reference device employing conventional PCBM as the ETM. The slightly lower FF could be mainly accounted for by the increased recombination in the polymer contained devices. This work demonstrated that polymeric materials can be used as efficient ETM in perovskite solar cells, and we believe this class of polymeric ETMs will further promote the performance of perovskite photovoltaic cells after extended investigation.

Enhanced performance in fluorene-free organometal halide perovskite light-emitting diodes using tunable, low electron affinity oxide electron injectors

Fluorene-free perovskite light-emitting diodes (LEDs) with low turn-on voltages, higher luminance and sharp, color-pure electroluminescence are obtained by replacing the F8 electron injector with ZnO, which is directly deposited onto the CH3NH3PbBr3 perovskite using spatial atmospheric atomic layer deposition. The electron injection barrier can also be reduced by decreasing the ZnO electron affinity through Mg incorporation, leading to lower turn-on voltages.

Enhanced reproducibility of the high efficiency perovskite solar cells via a thermal treatment

Thermal treatment of the cell samples after dc sputtering of the Au electrodes enhanced the reproducibility of the perovskite cell efficiencies because the thermal annealing induced the strong adhesion between each layer of the cells.

Thermally evaporable 5,10-dihydroindeno[2,1-a]indenes form efficient interfacial layers in organic solar cells

Several bis(diarylamino)dihydroindenoindene derivatives were synthesized for use as hole transporting materials (HTMs) in OPVs. An optimized device having the structure ITO/HTM/P3HT:PCBM/Ca/Al operated with a fill factor of 67.8%.

Enhanced efficiency of planar-heterojunction perovskite solar cells through a thermal gradient annealing process

An efficient gradient annealing approach has been developed to improve the surface morphology and coverage of perovskite films, thereby increasing the efficiency of perovskite solar cells.

Perovskite photovoltaics featuring solution-processable TiO2 as an interfacial electron-transporting layer display to improve performance and stability

In this study we used solution-processable crystalline TiO2 nanoparticles as an interfacial modified layer between the active layer and aluminum cathode to fabricate CH3NH3PbI3/PCBM-based planar heterojunction perovskite photovoltaic (PPV) devices. We optimized the performance of the PPV device prepared without TiO2 by varying the preheating temperature of the indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT) substrate, obtaining a power conversion efficiency (PCE) of 6.3% under simulated AM 1.5 G irradiation (100 mW cm(-2)). After incorporating the TiO2 layer, we obtained a much higher PCE of 7.0%. The TiO2-containing PPV device exhibited extremely high stability (retaining ∼96% of its PCE after 1000 h) under long-term storage in a dark N2-filled glove box; the unencapsulated device retained approximately 80% of its original efficiency (T80) after 1 week under ambient conditions (ISOS-D-1; defined as 23 °C/50% RH). In contrast, the normal device was sensitive to ambient conditions with a value of T80 at only 3 h. We attributed the improved device performance (PCE, stability) to the enhanced electron transporting, hole blocking, and barrier properties arising from the presence of the TiO2 layer.