Working area effects on the energetic distribution of trap states and charge dynamics of dye-sensitized solar cells

Abstract

Measuring the transient photoelectric signals (photovoltage or photocurrent) after optically perturbing dye-sensitized solar cells (DSSCs) can provide information about electron transport and recombination. Herein, the energetic distribution of trap states in different working areas of DSSCs (0.16 cm² <i>vs.</i> 1 cm²) and their impacts on charge transport and recombination were investigated by means of time-resolved charge extraction (TRCE), transient photovoltage (TPV) and transient photocurrent (TPC) measurements. The results indicated that increasing the working area deepened the energetic distribution of trap states (<i>i.e.</i>, increased the mean characteristic energy <i>k</i> _B <i>T</i> ₀), which hindered the electron transport within the photoanode, accelerated the electron recombination in high voltage regions, and reduced the charge collection efficiency. All abovementioned are the inherent reasons why the <i>J</i> _SC in larger working area cells is significantly smaller than that in smaller area cells (11.58 mA cm^-2 <i>vs.</i> 17.17 mA cm^-2). More importantly, as the investigation of high-efficiency large area solar cells is currently a promising research topic for new solar cells, we describe the importance of photoanode optimization to achieve high-efficiency DSSCs with large working area by improving charge collection efficiency.