Catalysis of Recombination and Its Limitation on Open Circuit Voltage for Dye Sensitized Photovoltaic Cells Using Phthalocyanine Dyes

Abstract

In order to increase the energy efficiency of dye-sensitized solar cells beyond 10%, an improved dye needs to be developed with greater light absorption in the red and near-infrared. Many dyes have been tested for this purpose; however, no dye with significant absorption beyond 750 nm has functioned properly. We have examined a series of ruthenium phthalocyanines, a dye class with large and tunable absorption in the red. For these dyes we observe a large reduction in the output voltage of the cells relative to the benchmark dye (N719). By examination of photovoltage transients and charge density measurements, we demonstrate that this reduction in voltage is caused by a 100-fold increase in the rate constant for recombination (iodine reduction) at the TiO2/electrolyte interface. N719, however, does not seem to catalyze this reaction. By examination of the literature, we propose that catalysis of the recombination reaction may be occurring for many other classes of potentially useful dyes including porphyrins, coumarins, perylenes, cyanines, merocyanines, and azulene. This widespread ability of the dye to catalyze recombination has not been appreciated before. This finding has important implications for future work to improve the red response of dye sensitized photovoltaics.

New generation solar cells: concepts, trends and perspectives

“…94 The diphenylphenoxy groups, in this case, act not only by avoiding macrocycle aggregation, but also, by blocking the interactions between the Pc and the electrolyte, reducing the so-called catalysis of recombination and unwanted dark currents. 95 Replacement of these bulky phenyl-based substituents by long alkyl chains led to the most successful Pc dye to date, PcS20 (Fig. 12).…”

Synthesis and Photovoltaic Properties of Two Dimensional Organic Dyes Containing Benzothiadiazole Unit

“…从图中可以看出, 有机染料 DH2 和 DD2 在固体膜中的吸收范围相对于溶液中的都有一定 程度的红移, 这是由于染料分子存在 J-型聚集的缘 故 [29] . Scan conditions: Pt electrodes for work and counter electrode, calomel electrode for reference electrode, and a scan rate of 100 mV/s, ferrocene as inner reference [31,32] . 其次, 电池的短路电流在 一定程度上受染料吸附量的影响 [33] , 两染料的摩尔吸 …”

Porphyrin Based Dye Sensitized Solar Cells

“…Such a process can only occur from an increased proximity of the acceptor species to the semiconductor surface. For the standard I -/I 3 -redox mediator, it has been proposed that most organic dyes (specifically including porphyrins) either attract I 3 -to the dye-semiconductor interface (Miyashita, Sunahara et al, 2008) or catalyse the recombination reaction with acceptor species in the electrolyte, such as I 3 -or the iodine radical I 2 - (O'Regan, López-Duarte et al, 2008). Several different strategies have been implemented in an attempt to improve the electron lifetime, and we now examine some of the major innovations which have lead to enhancements in the overall device V oc .…”