Resumo: A estabilidade ao longo do tempo das celulas solares sensibilizadas por corantes (Do ingles: dye-sensitized solar cells - DSSCs) e fundamental para a aplicacao desta tecnologia em larga escala. Nesta tese de Doutorado foram realizados estudos de estabilidade ao longo do tempo de DSSCs preparadas com mediador redox [Co(bpy)3]2+/3+ em eletrolito liquido ou eletrolito polimerico gel (5% m/m P(EO/EM/AGE) - poli(oxido de etileno-co-2(2-metoxietoxi)-etil glicidil eter-alil glicidil eter). Na primeira parte deste trabalho, as DSSCs foram sensibilizadas com o corante organico MK2 (acido 2-cianoacrilico 3-[5¿¿¿-(9-etil-9H-carbazol-3-il)-3¿,3¿¿,3¿¿¿,4-tetra-n-hexil- [2,2¿,5¿,2¿¿,5¿¿,2¿¿¿]-quadritiofen-5-il]) ou o corante contendo rutenio (II) Z907 (cis-bis(isotiocianato)(2,2f-bipiridil-4,4f-dicarboxilato)(4,4f-di-nonil-2f-bipiridil) rutenio (II)). Estes dispositivos foram submetidos a teste de estabilidade sob iluminacao no visivel. Ao final de 1000 h, as DSSCs com Z907 contendo eletrolito liquido e gel apresentaram comportamento similar, com valores de eficiencia de ¿Å=3,7 % } 0,7 e ¿Å=3,3 % } 0,4, respectivamente. Os dispositivos preparados com o corante MK2 e eletrolito liquido mantiveram 83% do valor de eficiencia inicial, enquanto os dispositivos com eletrolito gel retiveram 60%. A limitacao na difusao das especies Co3+ no eletrolito gel foi um dos fatores que acarretou a queda no desempenho. Constatou-se que o corante influencia na estabilidade ao longo do tempo das DSSCs, principalmente para dispositivos sensibilizados com o corante MK2 contendo eletrolito polimerico gel. Na segunda parte deste trabalho, foram realizados testes de estabilidade sob iluminacao UV, por 110 h, para dispositivos contendo duas abordagens de protecao UV: filtro UV no topo do dispositivo e um aditivo baseado em benzofenona no eletrolito, alem de uma combinacao de ambas abordagens. As DSSCs foram preparadas com o corante MK2 e o mediador [Co(bpy)3]2+/3+ no eletrolito liquido. O eletrolito gel foi preparado a partir de 5% (m/m) de P(EO/EM/AGE) e o aditivo benzofenona. O filtro UV sob a superficie do dispositivo foi mais eficiente na prevencao a degradacao do que o aditivo BZF no eletrólito Ver menos

Abstract: The long-term stability of dye-sensitized solar cells (DSSCs) is critical for the application of this technology in large scale. In this doctoral thesis, stability studies of DSSCs prepared with redox mediator [Co(bpy)3]2+/3+ using liquid or polymeric gel electrolyte (5% w/w P(EO/EM/AGE) - poly (ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether-allyl glycidyl ether) were investigated. In the first part of this thesis, the DSSCs were sensitized with an organic dye, MK2 (2-cyano-3-[5.-(9-ethyl-9H-carbazol-3-yl)- 3¡Ç,3¡È,3.,4-tetra-n-hexyl-[2,2¡Ç,5¡Ç,2¡È,5¡È,2.]-quarter thiophen-5- yl] acrylic acid) or ruthenium (II) based dye Z907 (cis-bis(isothiocyanato)(2,2¡¯-bipyridyl-4,4¡¯- dicarboxylato)(4,4¡¯-di-nonyl-2¡¯-bipyridyl)ruthenium(II)). The device¡¯s stability was tested under visible light. At the end of 1000 h, the Z907 cells containing liquid and gel electrolyte presented similar behavior with efficiency values of ¥ç=3.7%¡¾0.7 and ¥ç=3.3%¡¾0.4, respectively. The MK2 cells with liquid electrolyte maintained 83% of the initial efficiency value, while the gel electrolyte devices retained 60%. The diffusion limited transport of the Co3+ species was one factor that led to a drop in performance for the gel electrolyte devices. We found out that the nature of the dye influences the long-term stability of DSSCs, especially for devices sensitized with the MK2 dye containing polymeric gel electrolyte. In the second part of this work, stability tests were carried out in the devices for 110 h under UV radiation using two UV protection approaches: UV filter at the top of the device and a benzophenone based additive into the electrolyte; in addition to a combination of both methods. The DSSCs were prepared with the MK2 dye and the [Co(bpy)3]2+/3+ mediator for liquid electrolyte. The gel polymer electrolyte was prepared by addition of 5%(w/w) of P(EO/EM/AGE) and benzophenone additive. The UV filter under the top of the device was more efficient in preventing degradation than the BZF additive in the electrolyte Ver menos