High temperature stability of dye solar cells

Abstract

This work provides the state-of-the-art of dye solar cell chemical stability, assessed through accelerated ageing at temperatures up to 95°C and shows that solvent-based dye solar cells (DSCs) can pass 1000h/85°C tests with less than 10% loss of performance. Prior work is reviewed and compared with recent in-house results from DSCs based on three different solvents and two representative Ru dyes as well as the organic dye Y123. An “industrial DSC toolbox” of analysis methods, including IV testing at various light levels and in the dark, IPCE, EIS (at a single or at multiple cell voltages) and post mortem analysis, is used to better understand degradation mechanisms. For highly stable Z907-based cells, loss of performance due to high temperature ageing is dominated by loss of Voc, rather than Jsc or ff. Based on literature and this work, loss of I3−, resulting in partial bleaching of the electrolyte, appears to be strongly correlated with loss of performance upon high temperature storage, with the most stable systems investigated in this work displaying only marginal bleaching at temperatures above 80°C. Two in situ methods, EIS under light at zero DC current and IPCE in the sub 450nm region were used to quantitatively or semi-quantitatively gauge electrolyte I2 concentration within the active area. The nature of I3− degradation products still remains unknown. A lower limit of 68kJ/mol was estimated for the activation energy of the rate determining step, which leads to increased dark currents and thus lowered Voc upon high temperature storage. In addition there is evidence from IPCE of some changes to the dye structure, especially in MPN and GBL-based electrolyte systems. Dye desorption and degradation of platinum catalytic activity was shown to occur to some degree at the highest temperatures, but the impact on cell performance from these two mechanisms upon high temperature stress testing is only minor. Y123 showed particularly good stability at elevated temperature, surpassing even Z907 in terms of durability. Further improved device seals may lead to continued improvement of DSC stability under the harshest environmental conditions even for materials with a better performance-to-cost ratio than Z907 or Y123.