Wide applications of personal consumer electronics have triggered tremendous need for portable power sources featuring light-weight and mechanical flexibility. Perovskite solar cells offer a compelling combination of low-cost and high device performance. Here we demonstrate high-performance planar heterojunction perovskite solar cells constructed on highly flexible and ultrathin silver-mesh/conducting polymer substrates. The device performance is comparable to that of their counterparts on rigid glass/indium tin oxide substrates, reaching a power conversion efficiency of 14.0%, while the specific power (the ratio of power to device weight) reaches 1.96 kW kg(-1), given the fact that the device is constructed on a 57-μm-thick polyethylene terephthalate based substrate. The flexible device also demonstrates excellent robustness against mechanical deformation, retaining >95% of its original efficiency after 5,000 times fully bending. Our results confirmed that perovskite thin films are fully compatible with our flexible substrates, and are thus promising for future applications in flexible and bendable solar cells.

https://yylab.seas.ucla.edu/papers/ncomms10214.pdf

High-efficiency robust perovskite solar cells on ultrathin flexible substrates

Flexible and semitransparent organic solar cells (OSCs) have been regarded as the most promising photovoltaic devices for the application of OSCs in wearable energy resources and building-integrated photovoltaics. Therefore, the flexible and semitransparent OSCs have developed rapidly in recent years through the synergistic efforts in developing novel flexible bottom or top transparent electrodes, designing and synthesizing high performance photoactive layer and low temperature processed electrode buffer layer materials, and device architecture engineering. To date, the highest power conversion efficiencies have reached over 10% of the flexible OSCs and 7.7% with average visible transmittance of 37% for the semitransparent OSCs. Here, a comprehensive overview of recent research progresses and perspectives on the related materials and devices of the flexible and semitransparent OSCs is provided.

Flexible and Semitransparent Organic Solar Cells

Efficiency is crucial for organic light emitting diodes (OLEDs) to be energy-saving and to have a long lifetime for display and solid state lighting applications. Numerous approaches have been proposed to attain high efficiency OLEDs through the synthesis of novel organic materials, the design of light extraction structures and the design of efficiency-effective device architectures. In this report, we first summarise the efficiency records of OLED devices using fluorescent, phosphorescent, and thermally activated delay fluorescent materials. Importantly, we review all the available efficiency-effective device architectural approaches, which include using thin layer structures, low carrier injection barriers, high carrier mobility, balanced carrier injection, effective carrier confinement, effective host-to-guest energy transfer, effective recombination zone, effective exciton generation on the host, effective exciton confinement, p–i–n structures, and tandem structures. It is hoped that better device structures can therefore be devised upon suitable device engineering to achieve higher efficiency for OLED devices.

Approaches for fabricating high efficiency organic light emitting diodes

The emergence of smartphones and televisions with curved displays indicates that flexible organic light-emitting diodes (OLEDs) are marching steadily toward commercialization. Regardless of the significant step forward from laboratory to industry, flexible OLEDs are still facing enormous obstacles and challenges in realizing truly wearable, deformable, printable and low-cost electronic products for the future. How to develop highly flexible electrodes, optimize the device efficiency and greatly extend the operation lifetime are among the most important issues to be solved. In this regard, this review summarizes the recent achievements in flexible transparent conductive electrodes, device fabrication as well as light extraction technologies. Furthermore, the device operation stability is discussed with a focus on device degradation mechanisms and encapsulation methods. Some future prospects on new opportunities and research challenges in flexible OLEDs are also covered.

Recent advances in flexible organic light-emitting diodes

Flexible and wearable electronics is one major technology after smartphones. It shows remarkable application potential in displays and informatics, robotics, sports, energy harvesting and storage, and medicine. As an indispensable part and the cornerstone of these devices, soft metal electrodes (SMEs) are of great significance. Compared with conventional physical processes such as vacuum thermal deposition and sputtering, chemical approaches for preparing SMEs show significant advantages in terms of scalability, low-cost, and compatibility with the soft materials and substrates used for the devices. This review article provides a detailed overview on how to chemically fabricate SMEs, including the material preparation, fabrication technologies, methods to characterize their key properties, and representative studies on different wearable applications.

Chemical formation of soft metal electrodes for flexible and wearable electronics

Because of their mechanical flexibility, organic light-emitting diodes (OLEDs) hold great promise as a leading technology for display and lighting applications in wearable electronics. The development of flexible OLEDs requires high-quality transparent conductive electrodes with superior bendability and roll-to-roll manufacturing compatibility to replace indium tin oxide (ITO) anodes. Here, we present a flexible transparent conductor on plastic with embedded silver networks which is used to achieve flexible, highly power-efficient large-area green and white OLEDs. By combining an improved outcoupling structure for simultaneously extracting light in waveguide and substrate modes and reducing the surface plasmonic losses, flexible white OLEDs exhibit a power efficiency of 106 lm W–1 at 1000 cd m–2 with angular color stability, which is significantly higher than all other reports of flexible white OLEDs. These results represent an exciting step toward the realization of ITO-free, high-efficiency OLEDs for us...

High-performance flexible organic light-emitting diodes using embedded silver network transparent electrodes.

Enhancing light outcoupling in flexible organic light-emitting diodes (FOLEDs) is an important task for increasing their efficiencies for display and lighting applications. Here, a strategy for an angularly and spectrally independent boost in light outcoupling of FOLEDs is demonstrated by using plastic substrates with a low refractive index, consisting of a bioinspired optical coupling layer and a transparent conductive electrode composed of a silver network. The good transmittance to full-color emission (>94% over the whole visible wavelength range), ultralow sheet resistance to carrier injection (<5 Ω sq(-1)), and high tolerance to mechanical bending of the ameliorated plastic substrates synergistically optimize the device performance of FOLEDs. The maximum power efficiencies reach 47, 93, 56, and 52 lm W(-1) for red, green, blue, and white emissions, which are competitive with similarly structured OLEDs fabricated on traditional indium-tin-oxide (ITO) glass. This paradigm for light outcoupling enhancement in ITO-free FOLEDs offers additional features and design freedoms for highly efficient flexible optoelectronics in large-scale and low-cost manufacturing without the need for a high-refractive-index plastic substrate.

Outcoupling-Enhanced Flexible Organic Light-Emitting Diodes on Ameliorated Plastic Substrate with Built-in Indium–Tin-Oxide-Free Transparent Electrode

To fully unlock the potential of metallic electrodes in flexible polymer solar cells (PSCs), tuning their optical properties is urgently required. Here we report an efficient light harvesting scheme involving the combination of a silver mesowire grid-based front transparent electrode and a plasmonic meta-mirror-based back reflector electrode. As an alternative to the indium-tin-oxide transparent conductor, the silver mesowire grid on a plastic substrate enables the reduced ohmic loss with competitive mechanical, electrical and optical properties, verifying its superiority in large-area flexible devices. Further implementation of the plasmonic meta-mirror back reflector allows broadband enhancement of light harvesting efficiency over the entire visible wavelength range, yielding a power conversion efficiency of 9.50% due to a 23.2% increase in photocurrent compared to the reference flat device. Experimental and theoretical analysis of light propagation in PSCs elucidates that the optical harvesting enhancement benefits from the synergistic effects of wide-area redistribution of an optical field induced by the silver mesowire grid electrode and broadband recovery of photon loss via surface plasmon and scattering enabled by the meta-mirror back reflector. This method provides a convenient and scalable way for developing high-performance flexible PSCs towards the future photovoltaic applications.

Enhanced light harvesting in flexible polymer solar cells: synergistic simulation of a plasmonic meta-mirror and a transparent silver mesowire electrode

The invention discloses an organic solar cell which comprises an anode of a collection hole, a cathode of a collection electron, a photoactive layer and an electron transfer layer, wherein the photoactive layer generates a hole-electron pair and is arranged between the anode and the cathode, and the electron transfer layer is arranged between the cathode and the photoactive layer The electron transfer layer is a small organic molecule layer Luminescent materials are mingled in the small organic molecule layer The luminescent materials absorb the energy of a waveband and emit an optical waveband easily absorbed by the photoactive layer, wherein the waveband is not absorbed by the photoactive layer or the light absorption efficiency of the waveband is low Therefore, the light absorption efficiency of the photoactive layer is improved, and the photovoltaic conversion efficiency of the solar cell is effectively improved

Organic solar cell

Enhanced performance of polymer solar cells is reported by incorporating a solution-processed luminescent down-shifting (LDS) sensitizer, which is composed of a C545T fluorescent molecule doped tris(8-quinolinolato) aluminum (C545T:Alq3). An optimized LDS sensitizer can result in ∼15% enhancement in power conversion efficiency than the reference device with pristine Alq3. The performance enhancement is associated with the increase in photocurrent induced by LDS sensitizer, which is capable of absorbing short-wavelength solar spectrum and re-emitting long-wavelength light, which is complementary with the absorption spectrum of the active layer. This method provides a facile approach for high-performance polymer solar cell designs.

Hao-Jun Xie

Papers

High-performance flexible organic light-emitting diodes using embedded silver network transparent electrodes.

Outcoupling-Enhanced Flexible Organic Light-Emitting Diodes on Ameliorated Plastic Substrate with Built-in Indium–Tin-Oxide-Free Transparent Electrode

Enhanced light harvesting in flexible polymer solar cells: synergistic simulation of a plasmonic meta-mirror and a transparent silver mesowire electrode

Organic solar cell

Performance enhancement of polymer solar cells with luminescent down-shifting sensitizer