ITO‐Free and Fully Solution‐Processed Semitransparent Organic Solar Cells with High Fill Factors

Abstract

substrates accounts for 90% of the total energy required for manufacturing OPV. [ 8 ] To achieve ITO-free and fully solutionprocessed organic solar cells, the choice and processing of the anode and cathode electrodes are two challenges which require different considerations. Solutionprocessed bottom electrodes based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), AgNW and metallic grid electrodes are constantly narrowing the gap to ITO. [9][10][11][12][13][14][15][16] The main challenge for fully solution-processed devices remains the combination of a bottom and a top electrode, because the very thin and/ or soft underlying layers have to resist the solution deposition of the top electrode. Recently, solution-processed graphene, [ 17 ] AgNW, [ 18 , -21 ] silver nanoparticles [ 22 ] and PEDOT:PSS [ 23,24 ] were investigated as transparent top electrodes for organic solar cells. However, devices with incorporation of these top electrodes suffered either from the inferior optoelectronic properties of the electrodes or their multi-transfer processing procedure. On the other hand, aesthetic (semi-)transparent solar cells with special applications in windows, foldable curtains, buildings and clothes, etc., have recently gained much scientifi c attention and are considered to be the highest priority market for OPV. [ 25 ] We report here on materials and processes for reliable and cost-effi cient processing of ITO-free semitransparent organic solar cells from solution. Fully solution-processed organic solar Organic photovoltaic (OPV) solar cells that can be simply processed from solution are in the focus of the academic and industrial community because of their enormous potential to reduce cost. One big challenge in developing a fully solution-processed OPV technology is the design of a well-performing electrode system, allowing the replacement of ITO. Several solution-processed electrode systems were already discussed, but none of them could match the performance of ITO. Here, we report effi cient ITO-free and fully solution-processed semitransparent inverted organic solar cells based on silver nanowire (AgNW) electrodes. To demonstrate the potential of these AgNW electrodes, they were employed as both the bottom and top electrodes. Record devices achieved fi ll factors as high as 63.0%, which is comparable to ITO based reference devices. These results provide important progress for fully printed organic solar cells and indicate that ITO-free, transparent as well as non-transparent organic solar cells can indeed be fully solution-processed without losses.

Fully Solution-Processed Semitransparent Organic Solar Cells with a Silver Nanowire Cathode and a Conducting Polymer Anode

“…Despite their fully solution-processed nature, they are comparable in efficiency to previously reported semitransparent OSCs with ITO, which have been reported to have PCEs in the range 1.9 to 2.5 %. [27][28][29][30][31] The efficiencies also compare well with a very recent report by Guo et al 32 where PCEs of 2.3 % were achieved using AgNWs for both electrodes (although, in contrast to the devices described here, a ternary-blend of P3HT, …”

Semi-transparent polymer solar cells

“…AgNW was used as the material in the semi-transparent electrodes on both sides of the OPV cell 77,96 and, more recently, other alternatives to high vacuum processed transparent electrodes such as highly doped PEDOT, 73 PEDOT:PSS:CNTs, 67 graphene, 71 have been implemented in OPV cells. In general, the fully solution-processed cells have been shown to perform similarly to equivalent cells fabricated using a sputtered ITO electrode.…”

“…Several different options have been considered, such as low-temperature annealed indium tin oxide (ITO), [42][43][44][45][46][47][48] a three-layer architecture combining a dielectric layer, an ultra thin metal layer, and a second dielectric layer, [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] PEDOT, [65][66][67] silver grid, 68 graphene, [69][70][71] carbon nanotubes, 67,72 and silver nanowires (AgNW). [73][74][75][76][77][78] However, the need for a nondestructive deposition technique for the top semi-transparent electrode is probably not the major issue that semi-transparent OPV cells must overcome before becoming an industrially viable solution. Indeed, when the top electrode of an OPV cell is made semi-transparent, the capacity of the solar device to trap the electromagnetic field in the absorber layer diminishes.…”

Electrical limit of silver nanowire electrodes: Direct measurement of the nanowire junction resistance

“…1 Therefore, these networks have been implemented as transparent conducting electrodes in various optoelectronic devices, in particular, in small molecule or polymer-based solar cells and light emitting diodes. [1][2][3] Currently, they allow the fabrication of flexible lab-scale devices showing performance parity with devices comprising the considerably more brittle and sputter-deposited indium tin oxide (ITO). 4 Still, one important challenge is to further decrease the corresponding R S of AgNW networks, since future products are expected to be fabricated on large area and curved substrates.…”