Highly Efficient (>10%) Flexible Organic Solar Cells on PEDOT‐Free and ITO‐Free Transparent Electrodes

Abstract

We present a novel approach to fabricate flexible organic solar cells without indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). We use junctionfree metal nanonetworks (NNs) as transparent electrodes. The metal NNs are monolithically etched using nanoscale shadow masks, and they exhibit excellent optoelectronic performance. Furthermore, the optoelectrical properties of the NNs can be controlled by both the initial metal layer thickness and NN density. Hence, with an extremely thin silver layer, the appropriate density control of the networks can lead to high transmittance and low sheet resistance. Such NNs can be utilized for thin film devices without planarization by conductive materials such as PEDOT:PSS. As a result, we successfully fabricate a highly efficient flexible organic solar cell with a power conversion efficiency (PCE) of 10.6% and high device yield (93.8%) on PEDOT-free and ITO-free transparent electrodes. Furthermore, the flexible solar cell retains 94.3% of the initial PCE even after 3000 bending stress tests (strain: 3.13%).

The role of photon recycling in perovskite light-emitting diodes

“…Figure 4b shows that a maximum EQE of over 90% is achievable in this system with an electrode width of < 30 nm. This implies that dedicated design of nanostructured electrodes will bring further breakthroughs in LED efficiency with the aid of PR, in addition to their scattering and plasmon effects 3,16,44,45 . Moreover, although this calculation assumed dipole generation immediately beneath the electrode, charge carrier diffusion can improve the effective injection area of LEDs with nanostructured electrodes, without increase of parasitic absorption loss.…”

Realizing Ultrahigh Mechanical Flexibility and >15% Efficiency of Flexible Organic Solar Cells via a “Welding” Flexible Transparent Electrode

“…[ 1–4 ] Flexible organic solar cells (OSCs) that employ a plastic substrate and organic active layer provide the feasibility for producing high specific power (the ratio of power to device weight) and excellent intrinsic mechanical flexibility. [ 4–13 ] So far, the highest reported power conversion efficiency (PCE) for flexible single‐junction OSCs is 14.06%, [ 14 ] which is lower than that of the corresponding rigid device with the highest PCE of over 17%, [ 15 ] and even the large‐area rigid OSCs (> 1 cm 2 ) demonstrate a higher PCE of 15.3%. [ 10 ] The reasons for the inferior performance of the flexible OSCs originate from the different optoelectronic and physical properties between glass and plastic substrate materials as well as the deposited transparent electrodes.…”

“…[ 26–30 ] However, the solution‐processed AgNW network generally has a low coverage (less than 40%) and high junction resistance that would greatly deteriorate the conductivity and even the operative stability of the device as the AgNW junction locally concentrates heat by radiating under current flow. [ 9,31 ] Moreover, the randomly stacked and low‐adhesion AgNWs on the plastic substrate would likely trigger device short‐circuiting and reduce the mechanical peeling stability. Although this tangled problem can be partially mitigated by coating a conductive polymer, such as PH1000 onto the AgNW network film, the high parasitic absorption in the long‐wavelength region, and the acidity of PH1000 would reduce the light harvest and deteriorate the device stability.…”

“…To further improve the junction resistance and transmittance of this hybrid electrode, dry etching of a predeposited junction‐free thin metal film (AgNN) was performed using a precise Ag‐grid pattern. [ 9 ] The obtained 15 nm thick AgNN/ZnO hybrid electrode could achieve a low sheet resistance of 35.2 Ω sq −1 and a high transmittance of 91.6% (excluding the poly(ethylene terephthalate) (PET) substrate). However, the complexity and high energy consumption of fabrication processes, such as vacumm thermal evaporation, electrospinning, and ion‐beam etching technologies, would undoubtedly limit its practical application.…”

“…An additional critical defect for the AgNW electrode is low coverage, which may not only make an unfavorable electrical contact but also reduce the active area of the solar cells, thus limiting the device performance particularly with respect to the current. [ 9,31 ] To increase the electrode coverage without sacrificing the transmittance, AZO nanoparticles with low absorption coefficient in the long‐wavelength region were employed to fill the AgNW networks. Unfortunately, the AgNW network was not completely covered by the first‐time coated AZO, thus we spin‐coated AZO for the second time following a thermal annealing process.…”