Solution-processed Perovskite Solar Cells Research Articles

Solution-processed perovskite solar cells using environmentally friendly solvent system

Hybrid inorganic-organic perovskite solar cells have attracted great attention with power conversion efficiencies exceeding 20% using dimethylformamide or dimethyl sulfoxide for the deposition of the perovskite films. Replacing the toxic solvents with non-toxic solvents is one of the key challenges to realize industrial scale commercialization for the perovskite photovoltaics. Here, environmentally friendly solvent systems are employed for processing the perovskite active layer by a two-step spin-coating approach: aqueous Pb(NO3)2 is first spin-coated on mesoporous TiO2 film, and followed by spin-coating of methylammonium iodide in isopropanol. We found that the resulting perovskite was homogeneously covered on the TiO2 surface with relatively high coverage. The best performing perovskite solar cell shows a power conversion efficiency of 13.7% under standard conditions (AM1.5, 100mWcm−2).

Separating Bulk and Surface Contributions to Electronic Excited-State Processes in Hybrid Mixed Perovskite Thin Films via Multimodal All-Optical Imaging.

A comprehensive understanding of electronic excited-state phenomena underlying the impressive performance of solution-processed hybrid halide perovskite solar cells requires access to both spatially resolved electronic processes and corresponding sample morphological characteristics. Here, we demonstrate an all-optical multimodal imaging approach that enables us to obtain both electronic excited-state and morphological information on a single optical microscope platform with simultaneous high temporal and spatial resolution. Specifically, images were acquired for the same region of interest in thin films of chloride containing mixed lead halide perovskites (CH3NH3PbI3-xClx) using femtosecond transient absorption, time-integrated photoluminescence, confocal reflectance, and transmission microscopies. Comprehensive image analysis revealed the presence of surface- and bulk-dominated contributions to the various images, which describe either spatially dependent electronic excited-state properties or morphological variations across the probed region of the thin films. These results show that PL probes effectively the species near or at the film surface.

All solution processed perovskite solar cells with Ag@Au nanowires as top electrode

In this paper, solution-processed Au-coated Ag nanowires (Ag@Au NWs) was successfully fabricated as top electrode by spray deposition in planar perovskite solar cells (PVSCs) with structure ITO/PTAA:F4-TCNQ/MAPbI3/PC61BM/Ag@Au NWs, which shows favorable bandgap alignment. Sheet resistance of electrode and series resistance of solar cells over time as well as the stability of PVSCs were measured. The results indicate that the Au shell which serves as a physical separation layer sandwiched in between the perovskite/hole transporting layer (HTL) and the halide-reactive silver nanowires (Ag NWs) can significantly enhance the stability of PVSCs. The efficiency of solar cells employing Ag NWs as top electrode decreases rapidly within 10min while the efficiency of solar cells employing Ag@Au NWs still remains 85% of its original efficiency even after one week in air. The as-fabricated PVSCs exhibit a power conversion efficiency of 11.0% with an open-circuit voltage of 0.99V, a short-circuit current density of 18.5mA/cm2, and a fill factor of 64.3%. This work paves a way for realizing low cost, stable, all solution processable PVSCs.

Solution-processed perovskite-kesterite reflective tandem solar cells

Abstract Solution-processed solar cells are promising as low-cost alternatives to the first-generation solar cells. Combining two solution-processed devices in a tandem structure can potentially achieve a high efficiency while maintaining a relatively low fabrication cost. Here we present a tandem combining solution-processed perovskite and CZTSSe solar cells in a reflective configuration. The perovskite cell with a large bandgap acts as a spectral filter reflecting the sub-bandgap photons to a low bandgap CZTSSe cell. A total efficiency of 16.1% has been obtained in a four-terminal measurement, higher than each of the sub-cells. These results show the potential of solution-processed tandem solar cell with perovskite and kesterite in achieving a high efficiency with a low fabrication cost.

Ultraviolet-ozone surface modification for non-wetting hole transport materials based inverted planar perovskite solar cells with efficiency exceeding 18%

Non-wetting hole transport materials (HTMs) have great potential in facilitating large-sized perovskite crystal growth and enhancing device stability by opposing moisture ingress, However, the severe non-wetting issue limits the wide application of these materials in low-temperature solution-processed inverted planar perovskite solar cells (PVSCs), and corresponding devices are rarely reported. Here, a facile ultraviolet-ozone (UVO) modification method is demonstrated to overcome this issue. By carefully controlling the UVO modification time, the surface wettability of poly-TPD can be tuned without affecting the bulk properties of the film, hence perovskite films with desired grain size and excellent coverage can be deposited via a one-step spin-coating method. Benefiting from the high-quality perovskite, well-matched energy level alignment and hydrophobic property of poly-TPD, the resulting PVSCs show a champion power conversion efficiency of 18.19% with significantly enhanced stability as compared to the PEDOT:PSS counterparts. Moreover, the UVO modification approach also demonstrates its validity when being extended to other hydrophobic HTMs. This work not only provides a general strategy to broaden the selection pool of HTMs for solution-processed inverted planar PVSCs, but also may triggers the exploration of more advanced strategies to make non-wetting HTMs applicable in solution-processed inverted planar PVSCs.

Effect of thermal-convection-induced defects on the performance of perovskite solar cells

Thermal-convection-induced defects can cause huge loss in the power conversion efficiency of solution-processed perovskite solar cells. We investigated two types of convection in perovskite solution during the formation of perovskite films. By balancing the convection via special configurations of surface tension and boiling point in mixed γ-butyrolactone (GBL) and dimethylsulfoxide (DMSO), we removed microscopic defects such as rings, bumps, and crevices. The deposited perovskite films were smooth and dense, which enabled a high power conversion efficiency of 17.7% in a 1 cm2 cell area. We believe that the present strategy for controlling the convection can be helpful in improving the perovskite film quality for solvent-rich scalable solution processes of solar cells such as doctor blading, soft-cover deposition, printing, and slot-die coating.

Thermally Stable MAPbI3 Perovskite Solar Cells with Efficiency of 19.19% and Area over 1 cm2 achieved by Additive Engineering.

Solution-processed perovskite (PSC) solar cells have achieved extremely high power conversion efficiencies (PCEs) over 20%, but practical application of this photovoltaic technology requires further advancements on both long-term stability and large-area device demonstration. Here, an additive-engineering strategy is developed to realize a facile and convenient fabrication method of large-area uniform perovskite films composed of large crystal size and low density of defects. The high crystalline quality of the perovskite is found to simultaneously enhance the PCE and the durability of PSCs. By using the simple and widely used methylammonium lead iodide (MAPbI3 ), a certified PCE of 19.19% is achieved for devices with an aperture area of 1.025 cm2 , and the high-performing devices can sustain over 80% of the initial PCE after 500 h of thermal aging at 85 °C, which are among the best results of MAPbI3 -based PSCs so far.

Perovskite Films: Toward All Room‐Temperature, Solution‐Processed, High‐Performance Planar Perovskite Solar Cells: A New Scheme of Pyridine‐Promoted Perovskite Formation (Adv. Mater. 13/2017)

In article number 1604695, Wallace C.H. Choy and co-workers propose a novel room-temperature scheme of pyridine-promoted formation of perovskite films featuring large grain-sizes, and high crystallinity, while being free of residues. This new approach enables the fabrication of all room-temperature, solution-processed perovskite solar cells (PVSCs) with a record efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrate respectively.

Self-Functionalization Behind a Solution-Processed NiOx Film Used As Hole Transporting Layer for Efficient Perovskite Solar Cells.

Fabrication of solution-processed perovskite solar cells (PSCs) requires the deposition of high quality films from precursor inks. Frequently, buffer layers of PSCs are formed from dispersions of metal oxide nanoparticles (NPs). Therefore, the development of trustable methods for the preparation of stable colloidal NPs dispersions is crucial. In this work, a novel approach to form very compact semiconducting buffer layers with suitable optoelectronic properties is presented through a self-functionalization process of the nanocrystalline particles by their own amorphous phase and without adding any other inorganic or organic functionalization component or surfactant. Such interconnecting amorphous phase composed by residual nitrate, hydroxide, and sodium ions, proved to be fundamental to reach stable colloidal dispersions and contribute to assemble the separate crystalline nickel oxide NPs in the final film, resulting in a very homogeneous and compact layer. A proposed mechanism behind the great stabilization of the nanoparticles is exposed. At the end, the self-functionalized nickel oxide layer exhibited high optoelectronic properties enabling perovskite p-i-n solar cells as efficient as 16.6% demonstrating the pertinence of the presented strategy to obtain high quality buffer layers processed in solution at room temperature.

Degradation behavior of planar heterojunction CH3NH3PbI3 perovskite solar cells

The stability and degradation process of low-temperature, solution-processed planar heterojunction perovskite solar cells (PHJ-PSCs) with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al were studied in both nitrogen-filled glovebox and ambient environment (humidity ∼45%). The results suggested that PHJ-PSCs stored in glovebox without encapsulation showed good stability, and the power conversion efficiency (PCE) could be kept over 70% of original value even after 30days. As compared, PHJ-PSCs stored in ambient environment without encapsulation showed an obvious degradation, and the PCE was about 35% of original value just after 1h exposure in air. However, PHJ-PSCs fabricated with CH3NH3PbI3 thin films stored in ambient environment for the different times didn’t show obvious degradation and have the similar performance parameters, suggesting that the degradation of PHJ-PSCs mainly resulted from the interface issues rather than the attenuation of perovskite thin film itself. Furthermore, electrochemical impedance spectroscopy (EIS) characterization indicated that the degradation of photovoltaic performance parameters was prevailingly attributed to the interface degradation. The research provides good understanding to the stability and degradation process of low-temperature, solution-processed PHJ-PSCs, which would facilitate the stability improvement of PHJ-PSCs.

Moisture-driven phase transition for improved perovskite solar cells with reduced trap-state density

We report a mechanistic understanding of a moisture-driven intermediate-phase transition that improves the quality of perovskite thin films based on a lead-acetate precursor, improving the power-conversion efficiency. We clarify the composition of the intermediate phase and attribute the transition of this phase to the hygroscopic nature of the organic product, i.e., methylammonium acetate. Thermal annealing aids in the coarsening of the grains. These decoupled processes result in better crystal formation with a lower spatial and energetic distribution of traps. Thermal annealing of the films without exposure to air results in a faster intermediate-phase transition and grain coarsening, which occur simultaneously, leading to disorder in the films and a higher deep trap-state density. Our results indicate the need for a humid environment for the growth of high-quality perovskite films and provide insight into intermediate-phase dissociation and conversion kinetics. Thus, they are useful for the large-scale production of efficient solution-processed perovskite solar cells.

New Films on Old Substrates: Toward Green and Sustainable Energy Production via Recycling of Functional Components from Degraded Perovskite Solar Cells

The development of solution processable perovskite solar cells (PSCs) has progressed rapidly, and the their highest power conversion efficiency (PCE) has recently surpassed 22%. Further studies to promote market-oriented PSCs call for further reducing the manufacturing cost of the device and addressing the concerns about the possible outflow of toxic lead. To reduce the level of environmental pollution and prevent the health hazard caused by degraded devices (solid waste) and possible lead outflow and to conserve resources, we adopted low-temperature solution-processed, multirecycled glass/FTO/c-TiO2 (m-TiO2) substrates from the degraded devices to fabricate efficient planar heterojunction (PH) and mesoporous (M) PSCs in an environmentally friendly and energy-conserving manner. This is realized by simple and low-temperature processes, including organic solvent washing, ultrasonic cleaning, and UV–ozone treatment. After two rounds of substrate recycling, the PH PSC and M PSC still exhibited peak efficienci...

Efficient and stable solution-processed planar perovskite solar cells via contact passivation.

Planar perovskite solar cells (PSCs) made entirely via solution processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, these PSCs require an electron-selective layer that performs well with similar processing. We report a contact-passivation strategy using chlorine-capped TiO2 colloidal nanocrystal film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after dark recovery) of their initial performance after 500 hours of continuous room-temperature operation at their maximum power point under 1-sun illumination (where 1 sun is defined as the standard illumination at AM1.5, or 1 kilowatt/square meter).

Fully Solution-Processed n-i-p-Like Perovskite Solar Cells with Planar Junction: How the Charge Extracting Layer Determines the Open-Circuit Voltage.

Fully solution-processed direct perovskite solar cells with a planar junction are realized by incorporating a cross-linked [6,6]-phenyl-C61-butyric styryl dendron ester layer as an electron extracting layer. Power conversion efficiencies close to 19% and an open-circuit voltage exceeding 1.1 V with negligible hysteresis are delivered. A perovskite film with superb optoelectronic qualities is grown, which reduces carrier recombination losses and hence increases V oc .

Highly Efficient and Stable Perovskite Solar Cells by Interfacial Engineering Using Solution-Processed Polymer Layer

Solution-processed organo-lead halide perovskite solar cells with deep pinholes in the perovskite layer lead to shunt-current leakage in devices. Herein, we report a facile method for improving the performance of perovskite solar cells by inserting a solution-processed polymer layer between the perovskite layer and the hole-transporting layer. The photovoltaic conversion efficiency of the perovskite solar cell increased to 18.1% and the stability decreased by only about 5% during 20 days of exposure in moisture ambient conditions through the incorporation of a poly(methyl methacrylate) (PMMA) polymer layer. The improved photovoltaic performance of devices with a PMMA layer is attributed to the reduction of carrier recombination loss from pinholes, boundaries, and surface states of perovskite layer. The significant gain generated by this simple procedure supports the use of this strategy in further applications of thin-film optoelectronic devices.

Temperature-dependent charge transport in solution-processed perovskite solar cells with tunable trap concentration and charge recombination

Based on control of the perovskite film thickness, we investigate temperature-dependent charge carrier transport, recombination, traps, and solar cell behavior based on methylammonium lead triiodide films.

Microwave-synthesized tin oxide nanocrystals for low-temperature solution-processed planar junction organo-halide perovskite solar cells

Tin oxide nanoparticles prepared by microwave-assisted non-aqueous sol–gel were used to cast an electron transporting layer for organohalide perovskite solar cells showing, in average, high efficiencies thanks to the good optoelectronic properties of the material.

Optical and electronic properties of mixed halide (X = I, Cl, Br) methylammonium lead perovskite solar cells

We report on the fabrication and opto-electronic characterization of solution-processed planar heterojunction perovskite solar cells based on methylammonium (MA) lead halide derivatives, MAPbI3−xYx(Y = Cl, Br, I).

Synthesis and characterization of tetratriphenylamine Zn phthalocyanine as hole transporting material for perovskite solar cells

A soluble Zn phthalocyanine has been synthesized by tetra-substitution with triphenyl amine. This substance is functional as hole transporting material combined with organometal halide perovskite solar cells. The efficiency was slightly increased compared with previously studied insoluble copper phthalocyanine indicating that it is possible to make fully solution processed perovskite solar cells based on phthalocyanine as hole transporter.

A simple method to evaluate the effectiveness of encapsulation materials for perovskite solar cells

Solution processed perovskite solar cells are an exciting development in the field of photovoltaics achieving power conversion efficiencies of over 20%. Nevertheless, stability issues are still limiting the successful entry of this technology into the PV market. Rapid degradation has been observed and reported as the result of different factors, such as light, humidity and temperature, simultaneously present during real operation. It is felt within the PV community that proper, effective encapsulation is one of the key contributors to increasing perovskite lifetimes. This work presents a simple and effective method based on RGB (red, green, blue) colour measurements to track perovskite degradation to lead iodide (PbI2) using time lapse photography and thus evaluate the effectiveness/reliability of different encapsulation methods and materials. This technique gives a clear indication of when the perovskite has fully degraded and the impact of different encapsulants on degradation rate. This is supported by other analytical techniques, such as UV-Vis spectroscopy and XRD.