Abstract
ABSTRACT We explore the feasibility of Ag fiber meshes as electron transport layer for high-efficiency flexible Cu(In,Ga)Se2 (CIGS) solar cells. Woven meshes of Ag fibers after UV illumination and millisecond flash-lamp treatment results in a sheet resistance of 17 Ω/sq and a visible transmittance above 85%. Conductive Ag meshes are integrated into flexible CIGS cells as transparent conductive electrode (TCE) alone or together with layers of Al-doped ZnO (AZO) with various thickness of 0…900 nm. The Ag mesh alone is not able to function as a current collector. If used together with a thin AZO layer (50 nm), the Ag mesh markedly improves the fill factor and cell efficiency, in spite of the adverse mesh shadowing. When Ag mesh is combined with thicker (200 nm or 900 nm) AZO layers, no improvements in photovoltaic parameters are obtained. When comparing a hybrid TCE consisting of 50 nm AZO and Ag fiber mesh with a thick 900 nm reference AZO device, an improved charge carrier collection in the near-infrared range is observed. Regardless of the AZO thickness, the presence of Ag mesh slows down cell degradation upon mechanical tensile stress, which could be interesting for implementation into flexible thin film CIGS modules.
Highlights
Ag networks composed of one-dimensional nanowires and nano/microfibers have been considered as promising candidates for transparent conductive electrodes (TCEs), which are required as indispensable components in numerous optoelectronic devices such as touch panel displays, OLEDs, solar cells and smart windows [1,2]
Numerous reports on Ag networks and their applications are stimulated by advantageous characteristics of Ag networks such as (i) a low sheet resistance of 10 Ω/sq combined with a high optical transmittance above 80%, (ii) mechanical flexibility, (iii) nonvacuum deposition at low temperature that could be eventually implemented in a roll-to-roll manufacturing, and (iv) potentially lower cost as compared to widely used transparent conducting oxide (TCO) such as sputtered indium tin oxide (ITO)
Kim et al [7] fabricated Ag network-based hybrid TCEs for CIGS solar cells by sandwiching a layer of Ag nanowire between ZnO and Al-doped ZnO (AZO) layers to restore the loose contact between Ag nanowire and the CdS buffer layer enhancing the lateral conduction of hybrid TCEs; the fabricated CIGS cells showed an efficiency of 11.03%, while the reference cell with sputtered ITO had an efficiency of 10.91%
Summary
Ag networks composed of one-dimensional nanowires and nano/microfibers have been considered as promising candidates for transparent conductive electrodes (TCEs), which are required as indispensable components in numerous optoelectronic devices such as touch panel displays, OLEDs, solar cells and smart windows [1,2]. Singh et al [11] and Wang et al [10] combined sputtered ZnO or nonvacuum-processed AZO with Ag nanowire to improve the adherence of Ag network with the underlying intrinsic ZnO layer, achieving up to 14%efficient CIGS solar cells on glass substrates [10]. Conductive Ag networks are fabricated by draw-spinning on a polyethylene terephthalate (PET) substrate and laminated onto flexible CIGS solar cells that are terminated with either intrinsic ZnO or AZO. This approach is more straightforward from the technical point of view as it isolates the fabrication of the Ag mesh and the CIGS cell. ● In the case of hybrid TCEs composed of Ag mesh and AZO, can the presence of Ag mesh improve any of the photovoltaic parameters as compared to reference AZO electrodes of various thicknesses? ● Can the presence of the Ag mesh slow down the degradation of solar cells subjected to bending or tensile stresses?
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