Simple Bar‐Coating Process for Fabrication of Flexible Top‐Illuminated Polymer Solar Cells on Metallic Substrate

Abstract

printing. Moreover, TI-PSCs have shown poor photoconversion effi ciency (PCE) because of diffi culties in forming an active layer on a hydrophobic bottom refl ective electrode. [ 61 ] To realize TI-PSCs on metallic substrate, the printing method must: (1) use a simple noncontact printing technique to avoid scratching the bottom refl ective electrode, (2) be optimized to yield a uniform and reproducible active layer, and (3) be easily used in R2R processes to allow mass production. (4) Also, TI-PSCs on metallic substrate must have PCE comparable to those of TI-PSC on glass or plastic substrates. Therefore, to achieve highly effi cient R2R-processed TI-PSCs on metallic substrate, a printing process must be developed and a device structure must be designed.Hereby, we fabricated TI-PSCs on metallic substrate by using a simple bar-coating method to deposit an active layer of lowbandgap donor and fullerene acceptor (PTB7:PCBM) ( Figure 1 ). Because bar-coating, used in this work, is a noncontact printing technique, the thickness of the PTB7:PCBM layer was tuned without scratching the refl ective bottom electrode, leading to apply for large-area R2R fabrication of fl exible PSCs. To achieve a fl exible metallic substrate, we developed a simple way to prepare the Cu foil by vacuum-depositing Cu to 50 nm thickness on a glass substrate, then electroplating. The result was 100 µm thick Cu foils that could be peeled from the glass substrate, and that had chemically clean and atomically fl at surface and are lightweight, fl exible, strong, thermally stable, and have low WVTR. These advantages were exploited to demonstrate TI-PSCs. After optimizing the bar-coating process and designing the device structure, TI-PSCs were successfully fabricated on fl exible Cu foil; they had an average PCE of 5.7%, which is comparable to the PCE = 5.9% of TI-PSCs on rigid glass substrate and is the highest yet obtained by printed fl exible PSCs.Spin-coating and bar-coating were used to deposit largearea PTB7:PCBM layers. For spin-coating, 200 µL of precursor solution was dropped on the center of a glass substrate (area = 16 cm 2 ), which was then spun at 1800 rpm ( Figure 2 a). The PTB7:PCBM layer was uniform at the center, but not at the edge of the substrate because centrifugal force during spinning prevented the solution from wetting the surface. To obtain uniform layer, 600 µL of solution is required for spin-coating method ( Figure S1, Supporting Information). In contrast, barcoating 50 µL of precursor solution resulted in a conformal layer of PTB7:PCBM on a large substrate (area = 64 cm 2 ) (Figure 2 b). These results indicate that bar-coating allows the PTB7:PCBM layer to be more uniformly deposited on a larger substrate than the spin-coating method.Optical transmittance, OT (i.e., in visible spectrum 400 ≤ λ ≤ 800 nm) of bar-coated PTB7:PCBM layers decreased Flexible polymer solar cells (PSCs) are light weight, inexpensive, and compatible with large-area roll-to-roll (R2R) fabrication. [1][2][3][4][5] For a fl exible PSC to be chemicall...

Towards all-solution-processed top-illuminated flexible organic solar cells using ultrathin Ag-modified graphite-coated poly(ethylene terephthalate) substrates

“…Therefore, further efforts are needed to modify the surface properties of the graphite/PET substrate before it can be used for application in top-illuminated FOSCs. This aside, the efficiency of the top-illuminated FOSCs reported today is still relatively low compared with that of the FOSCs with a regular device configuration [20,27,28]. In addition, it is reported that heat rejection of solar cells plays an important role in the overall performance of photovoltaic-based devices and can significantly affect the overall heating, lighting, and cooling costs of a building [29][30][31].…”