Metal electrode-free perovskite solar cells with transfer-laminated conducting polymer electrode

All-printed organic photodetectors with metal electrodes enabled by one-step solvent-mediated transfer printing technology

A one-step solvent-mediated transfer printing technology (sTPT) is proposed to fabricate printable silver (Ag) electrodes. This simple approach can realize the residuals in the active layer serving as the mediator due to the capillary action without the use of any additional solvent. The as-cast polydimethylsiloxane (PDMS) was used as the stamp in the fabrication process. The residual solvent and the as-cast PDMS stamps simplified the fabrication process, while the transfer-printed Ag electrodes presented favorable conductivity and improved hydrophobicity due to the presence of residual PDMS on the surface of Ag, indicating the superiority as the top electrode for organic photodetectors (OPDs). Compared to the devices with the top Ag electrodes fabricated by the conventional evaporation method, we demonstrated that the OPDs with transfer-printed Ag electrodes presented better performance than that of the reference devices, including suppressed dark current, enlarged linear dynamic range, shortened response time, and optimized durability. These improved performances can be attributed to the fewer traps at the interface between the active layer and Ag electrodes. The sTPT may be a promising method for the fabrication of OPDs owing to the simplified fabrication process and enhanced device performance.

Halide Perovskites and Their Derivatives for Efficient, High-Resolution Direct Radiation Detection: Design Strategies and Applications

The past decade has witnessed a rapid rise in the performance of optoelectronic devices based on lead-halide perovskites (LHPs). The large mobility-lifetime products and defect tolerance of these materials, essential for optoelectronics, also make them well-suited for radiation detectors, especially given the heavy elements present, which is essential for strong X-ray and γ-ray attenuation. Over the past decade, LHP thick films, wafers, and single crystals have given rise to direct radiation detectors that have outperformed incumbent technologies in terms of sensitivity (reported values up to 3.5 × 106 µC Gyair -1 cm-2 ), limit of detection (directly measured values down to 1.5 nGyair s-1 ), along with competitive energy and imaging resolution at room temperature. At the same time, lead-free perovskite-inspired materials (e.g., methylammonium bismuth iodide), which have underperformed in solar cells, have recently matched and, in some areas (e.g., in polarization stability), surpassed the performance of LHP detectors. These advances open up opportunities to achieve devices for safer medical imaging, as well as more effective non-invasive analysis for security, nuclear safety, or product inspection applications. Herein, the principles behind the rapid rises in performance of LHP and perovskite-inspired material detectors, and how their properties and performance link with critical applications in non-invasive diagnostics are discussed. The key strategies to engineer the performance of these materials, and the important challenges to overcome to commercialize these new technologies are also discussed.

Lamination methods for the fabrication of perovskite and organic photovoltaics

Perovskite solar cells (PSCs) have shown rapid progress in a decade of extensive research and development, aiming now towards commercialization. However, the development of more facile, reliable, and reproducible manufacturing techniques will be essential for industrial production. Many lamination methods have been initially designed for organic photovoltaics (OPVs), which are conceptually similar to PSCs. Lamination could provide a low-cost and adaptable technique for the roll-to-roll production of solar cells. This review presents an overview of lamination methods for the fabrication of PSCs and OPVs. The lamination of different electrodes consisting of various materials such as metal back contacts, photoactive layers, hole transport layers (HTLs), and electron transport layers (ETLs) is discussed. The efficiency and stability of the laminated devices are also presented. Finally, the challenges and opportunities of laminated solar cells are discussed.

Metal Electrode-Free Halide Perovskite-Based Flexible Ultraviolet-C Photodetector with Large Area

Ultraviolet-C (UVC) photodetector has appealed to a numerous number of research owing to its manifold applications in wireless communication, flame monitoring, and medicine. However, in addition to superior performance and high stability of recent studies, scalability and production cost are important factors for commercialization and practical implementation. In this study, a halide perovskite-based UVC photodetector was fabricated using spin-coating process and low-temperature annealing. Corning® Willow® Glass was selected as the substrate for the bottom-illuminated device due to its flexibility and exceptional optical transmission (approximately 60%) in the deep-UV region. The device had a vertical structure with a large active area (1 cm²) owing to the judicious utilization of electrodes. Under bent state with a curvature radius of 25 mm, the as-fabricated device exhibited high response and repeatability with an on/off ratio of 9.57 × 10³, a fast response speed of 45/46 ms (rise/fall times) at zero bias under the illumination of a 254-nm UV lamp. The results are based on a flexible and lightweight photodetector without the utilization of notable metal electrodes.

Electrode Engineering in Halide Perovskite Electronics: Plenty of Room at the Interfaces

Contact engineering is a prerequisite for achieving desirable functionality and performance of semiconductor electronics, which is particularly critical for organic-inorganic hybrid halide perovskites due to their ionic nature and highly reactive interfaces. Although the interfaces between perovskites and charge-transporting layers have attracted lots of attention due to the photovoltaic and light-emitting diode applications, achieving reliable perovskite/electrode contacts for electronic devices, such as transistors and memories, remains as a bottleneck. Herein, a critical review on the elusive nature of perovskite/electrode interfaces with a focus on the interfacial electrochemistry effects is presented. The basic guidelines of electrode selection are given for establishing non-polarized interfaces and optimal energy level alignment for perovskite materials. Furthermore, state-of-the-art strategies on interface-related electrode engineering are reviewed and discussed, which aim at achieving ohmic transport and eliminating hysteresis in perovskite devices. The role and multiple functionalities of self-assembled monolayers that offer a unique approach toward improving perovskite/electrode contacts are also discussed. The insights on electrode engineering pave the way to advancing stable and reliable perovskite devices in diverse electronic applications.

Practical Demonstration of Deep-Ultraviolet Detection with Wearable and Self-Powered Halide Perovskite-Based Photodetector

Flexible and self-powered photodetectors (PDs) have become one of the most popular topics, attracting researchers in the field of optoelectronic applications. In this study, for the first time, we demonstrate partial discharge detection in a practical environment with a prepared flexible device. Poly(vinylidene fluoride) (PVDF) is utilized as a highly transparent material in the UVC region, to create a flexible substrate with the antihumidity property. A detector that uses a mixed-halide perovskite (FAPbI₃)_1-x(MAPbBr₃)_x as the photoactive material is constructed in a vertical structure on the as-prepared hydrophobic PVDF substrate. The fabricated device exhibits good performance with a fast response speed (t_rise = 82 ms, t_fall = 64 ms) and a high detectivity of 7.21 × 10¹⁰ Jones at zero bias under 254 nm UV illumination, along with superior mechanical flexibility at various bending angles. Additionally, the air-exposure stability and reproducibility of the as-prepared device exhibit almost the original performance after 6 weeks of storage. For practical applications, we demonstrate a facile and sensitive detection for UVC leakage from a germicidal lamp and simulated a partial discharge system using our PD without energy consumption. These results indicate that this new approach may be useful and convenient for the detection of the partial discharge as well as for several practical applications.

Recent Progress in Developing Monolithic Perovskite/Si Tandem Solar Cells

Monolithic perovskite/Silicon tandem solar cells have reached a certified efficiency of 29. 1% in recent years. In this review, we discuss material design for monolithic perovskite/Si tandem solar cells, with the focus on the top-cell development to improve their performance. Firstly, we introduce different types of transparent electrodes with high transmittance and low sheet-resistance used in tandem solar cells. We then discuss the development of the wide-bandgap perovskite absorber for top-cells, especially the strategies to obtain the perovskite layers with good efficiency and stability. In addition, as a special functional layer in tandem solar cells, the recombination layers play an important role in device performance, wherein different configurations are summarized. Furthermore, tandem device cost analysis is discussed. This review summarizes the progress of monolithic perovskite/Silicon tandem solar cells in a pragmatic perspective, which may promote the commercialization of this technology.

Recent Progress in Metal Halide Perovskite-Based Tandem Solar Cells

Metal halide perovskite (MHP)-based tandem solar cells are a promising candidate for use in cost-effective and high-performance solar cells that can compete with fossil fuels. To understand the research trends for MHP-based tandem solar cells, a general introduction to single-junction and multiple-junction MHP solar cells and the configuration of tandem devices is provided, along with an overview of the recent progress regarding various MHP-based tandem cells, including MHP/crystalline silicon, MHP/CuInGaS, MHP/organic photovoltaic, MHP/quantum dot, and all-perovskite tandem cell. Future research directions for MHP-based tandem solar cells are also discussed.

Reproducible Dry Stamping Transfer of PEDOT:PSS Transparent Top Electrode for Flexible Semitransparent Metal Halide Perovskite Solar Cells

A semitransparent flexible metal halide perovskite (MHP) solar cells were demonstrated by reproducible dry stamping transfer of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS, PH1000) transparent flexible top electrode onto poly(ethylene terephthalate) (PET)/indium tin oxide (ITO)/PEDOT:PSS (AI4083)/MHP/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). The reproducible transfer of the PEDOT:PSS top electrode was enabled by the modification of PEDOT:PSS with poly(ethylene imine) (PEI)/2-methoxyethanol (2-MEA) solution. In addition, the PEI/2-MEA modification to PEDOT:PSS resulted in improved conductivity and reduced work function of the top electrode. Therefore, we could fabricate highly efficient flexible semitransparent MHP solar cells with >13% (active area = 1 cm²) power conversion efficiency.

Research Progress on Polymer Solar Cells Based on PEDOT:PSS Electrodes

Solution-processed polymer solar cells (PSCs) have attracted dramatically increasing attention over the past few decades owing to their advantages of low cost, solution processability, light weight, and excellent flexibility. Recent progress in materials synthesis and devices engineering has boosted the power conversion efficiency (PCE) of single-junction PSCs over 17%. As an emerging technology, it is still a challenge to prepare solution-processed flexible electrodes for attractive flexible PSCs. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is one of the most promising candidates for electrodes due to its high conductivity (>4000 S/cm), excellent transmittance (>90%), intrinsically high work function (W_F > 5.0 eV), and aqueous solution processability. To date, a great number of single-junction PSCs based on PEDOT:PSS electrodes have realized a PCE over 12%. In this review, we introduce the current research on the conductive complex PEDOT:PSS as well as trace the development of PEDOT:PSS used in electrodes for high performance PSCs and perovskite solar cells. We also discuss and comment on the aspects of conductivity, transmittance, work-function adjustment, film preparing methods, and device fabrications. A perspective on the challenges and future directions in this field is be offered finally.

Shear-Enhanced Transfer Printing of Conducting Polymer Thin Films

Polymer conductors that are solution-processable provide an opportunity to realize low-cost organic electronics. However, coating sequential layers can be hindered by poor surface wetting or dissolution of underlying layers. This has led to the use of transfer printing where solid film inks are transferred from a donor substrate to partially fabricated devices using a stamp. This approach typically requires favorable adhesion differences between the stamp, ink, and receiving substrate. Here, we present a shear-assisted organic printing (SHARP) technique that employs a shear load on a post-less polydimethylsiloxane (PDMS) elastomer stamp to print large-area polymer films that can overcome large unfavorable adhesion differences between the stamp and receiving substrate. We explore the limits of this process by transfer printing poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) films with varied formulation that tune the adhesive fracture energy. Using this platform, we show that the SHARP process is able to overcome a 10-fold unfavorable adhesion differential without the use of a patterned PDMS stamp, enabling large-area printing. The SHARP approach is then used to print PEDOT:PSS films in the fabrication of high-performance semitransparent organic solar cells.

A Semitransparent Inorganic Perovskite Film for Overcoming Ultraviolet Light Instability of Organic Solar Cells and Achieving 14.03% Efficiency

Organic solar cells (OSCs) can be unstable under ultraviolet (UV) irradiation. To address this issue and enhance the power conversion efficiency (PCE), an inorganic-perovskite/organic four-terminal tandem solar cell (TSC) based on a semitransparent inorganic CsPbBr₃ perovskite solar cell (pero-SC) as the top cell and an OSC as bottom cell is constructed. The high-quality CsPbBr₃ photoactive layer of the planar pero-SC is prepared with a dual-source vacuum coevaporation method, using stoichiometric precursors of CsBr and PbBr₂ with a low evaporation rate. The resultant opaque planar pero-SC exhibits an ultrahigh open-circuit voltage of 1.44 V and the highest reported PCE of 7.78% for a CsPbBr₃ -based planar pero-SC. Importantly, the devices show no degradation after 120 h UV light illumination. The related semitransparent pero-SC can almost completely filter UV light and well maintain photovoltaic performance; it additionally shows an extremely high average visible transmittance. When it is used to construct a TSC, the top pero-SC acting as a UV filter can utilize UV light for photoelectric conversion, avoiding the instability problem of UV light on the bottom OSC that can meet the industrial standards of UV-light stability for solar cells, and leading to the highest reported PCE of 14.03% for the inorganic-perovskite/organic TSC.

Stacking Sequence and Acceptor Dependence of Photocurrent Spectra and Photovoltage in Organic Two-Junction Devices

Both single-junction and tandem organic photovoltaic cells have been well developed. A tandem cell contains two junctions with a charge recombination layer (CRL) inserted between the two junctions. So far, there is no detailed report on how the device will perform that contains two junctions but without a CRL in between. In this work, we report the photocurrent spectra and photovoltage output of the devices that contains two bulk-heterojunctions (BHJ) stacked directly on top of each other without a CRL. The top active layer is prepared by transfer printing. The photocurrent response spectra and photovoltage are found to be sensitive to stacking sequence and the selection of electron acceptors. The open-circuit voltage of the devices (up to 1.09 V) can be higher than the devices containing either junction layer. The new phenomenon in the new device architecture increases the versatility of the optoelectronic devices based on organic semiconductors.

Fully Printable Organic and Perovskite Solar Cells with Transfer-Printed Flexible Electrodes

The perovskite solar cells (PSCs) and organic solar cells (OSCs) with high performance were fabricated with transfer-printed top metal electrodes. We have demonstrated that PSCs and OSCs with the top Au electrodes fabricated by using the transfer printing method have comparable or better performance than the devices with the top Au electrodes fabricated by using the conventional thermal evaporation method. The highest PCE of the PSCs and OSCs with the top electrodes fabricated using the transfer printing method achieved 13.72% and 2.35%, respectively. It has been investigated that fewer defects between the organic thin films and Au electrodes exist by using the transfer printing method which improved the device stability. After storing the PSCs and OSCs with the transfer-printed electrodes in a nitrogen environment for 97 and 103 days without encapsulation, the PSCs and OSCs still retained 71% and 91% of their original PCEs, respectively.

Efficient Colorful Perovskite Solar Cells Using a Top Polymer Electrode Simultaneously as Spectrally Selective Antireflection Coating

Organometal halide perovskites have shown excellent optoelectronic properties and have been used to demonstrate a variety of semiconductor devices. Colorful solar cells are desirable for photovoltaic integration in buildings and other aesthetically appealing applications. However, the realization of colorful perovskite solar cells is challenging because of their broad and large absorption coefficient that commonly leads to cells with dark-brown colors. Herein, for the first time, we report a simple and efficient strategy to achieve colorful perovskite solar cells by using the transparent conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) as a top electrode and simultaneously as an spectrally selective antireflection coating. Vivid colors across the visible spectrum are attained by engineering optical interference effects among the transparent PEDOT:PSS polymer electrode, the hole-transporting layer and the perovskite layer. The colored perovskite solar cells display power conversion efficiency values from 12.8 to 15.1% (from red to blue) when illuminated from the FTO glass side and from 11.6 to 13.8% (from red to blue) when illuminated from the PEDOT:PSS side. The new approach provides an advanced solution for fabricating colorful perovskite solar cells with easy processing and high efficiency.

Nonreduction-Active Hole-Transporting Layers Enhancing Open-Circuit Voltage and Efficiency of Planar Perovskite Solar Cells

Inverted planar perovskite solar cells using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole-transporting layer (HTL) are very attractive because of their low-temperature and easy processing. However, the planar cells with the PEDOT:PSS HTL typically display lower open-circuit voltage (V_OC) (about 0.90 V) than that of devices with TiO₂-based conventional structure (1.0-1.1 V). The underlying reasons are still not clear. In this work, we report the PEDOT:PSS that is intrinsically p-doped can be chemically reduced by methylamine iodide (MAI) and MAPbI₃. The reaction reduces the work function (WF) of PEDOT:PSS, which suppresses the efficient hole collection and yields lower V_OC. To overcome this issue, we adopt undoped semiconducting polymers that are intrinsically nonreduction-active (NRA) as the HTL for inverted planar perovskite solar cells. The cells display enhanced V_OC from 0.88 ± 0.04 V (PEDOT:PSS HTL, reference cells) to 1.02 ± 0.03 V (P3HT HTL) and 1.04 ± 0.03 V (PTB7 and PTB-Th HTL). The power conversion efficiency (PCE) of the devices with these NRA HTL reaches about 17%.

p-type Li, Cu-codoped NiOx hole-transporting layer for efficient planar perovskite solar cells

p-type inorganic hole transport materials of Li, Cu-codoped NiOx films were deposited using a simple solution-based process. The as-prepared films were used as hole selective contacts for lead halide perovskite solar cell. An enhanced power conversion efficiency of 14.53% has been achieved due to the improved electrical conductivity and optical transmittance of the Li, Cu-codoped NiOx electrode interlayer.

Transfer-printing of active layers to achieve high quality interfaces in sequentially deposited multilayer inverted polymer solar cells fabricated in air

Polymer solar cells (PSCs) are greatly influenced by both the vertical concentration gradient in the active layer and the quality of the various interfaces. To achieve vertical concentration gradients in inverted PSCs, a sequential deposition approach is necessary. However, a direct approach to sequential deposition by spin-coating results in partial dissolution of the underlying layers which decreases the control over the process and results in not well-defined interfaces. Here, we demonstrate that by using a transfer-printing process based on polydimethylsiloxane (PDMS) stamps we can obtain increased control over the thickness of the various layers while at the same time increasing the quality of the interfaces and the overall concentration gradient within the active layer of PSCs prepared in air. To optimize the process and understand the influence of various interlayers, our approach is based on surface free energy, spreading parameters and work of adhesion calculations. The key parameter presented here is the insertion of high quality hole transporting and electron transporting layers, respectively above and underneath the active layer of the inverted structure PSC which not only facilitates the transfer process but also induces the adequate vertical concentration gradient in the device to facilitate charge extraction. The resulting non-encapsulated devices (active layer prepared in air) demonstrate over 40% increase in power conversion efficiency with respect to the reference spin-coated inverted PSCs.

A transparent, solvent-free laminated top electrode for perovskite solar cells

A simple lamination process of the top electrode for perovskite solar cells is demonstrated. The laminate electrode consists of a transparent and conductive plastic/metal mesh substrate, coated with an adhesive mixture of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, and sorbitol. The laminate electrode showed a high degree of transparency of 85%. Best cell performance was achieved for laminate electrodes prepared with a sorbitol concentration of ~30 wt% per milliliter PEDOT:PSS dispersion, and using a pre-annealing temperature of 120°C for 10 min before lamination. Thereby, perovskite solar cells with stabilized power conversion efficiencies of (7.6 ± 1.0)% were obtained which corresponds to 80% of the reference devices with reflective opaque gold electrodes.

Low-temperature-processed efficient semi-transparent planar perovskite solar cells for bifacial and tandem applications

Semi-transparent perovskite solar cells are highly attractive for a wide range of applications, such as bifacial and tandem solar cells; however, the power conversion efficiency of semi-transparent devices still lags behind due to missing suitable transparent rear electrode or deposition process. Here we report a low-temperature process for efficient semi-transparent planar perovskite solar cells. A hybrid thermal evaporation–spin coating technique is developed to allow the introduction of PCBM in regular device configuration, which facilitates the growth of high-quality absorber, resulting in hysteresis-free devices. We employ high-mobility hydrogenated indium oxide as transparent rear electrode by room-temperature radio-frequency magnetron sputtering, yielding a semi-transparent solar cell with steady-state efficiency of 14.2% along with 72% average transmittance in the near-infrared region. With such semi-transparent devices, we show a substantial power enhancement when operating as bifacial solar cell, and in combination with low-bandgap copper indium gallium diselenide we further demonstrate 20.5% efficiency in four-terminal tandem configuration.

Perovskite solar cells already exhibit large efficiencies above 20%. Here, the authors use a low temperature sputtering process to fabricate semi-transparent perovskite solar cells, demonstrating bifacial operation and a 4-terminal tandem with CIGS solar cells surpassing single junction cells.

Semitransparent Fully Air Processed Perovskite Solar Cells

Semitransparent solar cells are highly attractive for application as power-generating windows. In this work, we present semitransparent perovskite solar cells that employ conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (

PEDOT

PSS) film as the transparent counter electrode. The

PEDOT

PSS electrode is prepared by transfer lamination technique using plastic wrap as the transfer medium. The use of the transfer lamination technique avoids the damage of the CH3NH3PbI3 perovskite film by direct contact of

PEDOT

PSS aqueous solution. The semitransparent perovskite solar cells yield a power conversion efficiency of 10.1% at an area of about 0.06 cm(2) and 2.9% at an area of 1 cm(2). The device structure and the fabrication technique provide a facile way to produce semitransparent perovskite solar cells.

Conductivity Enhancement of PEDOT:PSS Films via Phosphoric Acid Treatment for Flexible All-Plastic Solar Cells

Highly conductive polymer films on plastic substrates are desirable for the application of flexible electronics. Here, we report the conductivity of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (

PEDOT

PSS) can be enhanced to 1460 S/cm via phosphoric acid (H3PO4) treatment. The conductivity enhancement is associated with the partial removal of PSS from the film. The H3PO4 treatment is compatible with plastic substrates, while sulfuric acid (H2SO4) can easily damage the plastic substrate. With the flexible electrode of poly(ether sulfone) (PES)/H3PO4-treated

PEDOT

PSS, we have demonstrated flexible all-plastic solar cells (PES/H3PO4-treated

PEDOT

PSS/PEI/P3HT:ICBA/EG-PEDOT:PSS). The cells exhibit an open-circuit voltage of 0.84 V, a fill factor of 0.60, and a power conversion efficiency of 3.3% under 100 mW/cm(2) white light illumination.

Low temperature processed ITO-free perovskite solar cells without a hole transport layer

We successfully employ low temperature processed conductive polymer PH1000 as an alternative electrode of ITO to fabricate HTL-free PSCs. The best device shows efficiency up to 9.31%, providing a much simpler architecture for the application of PSC.