Department of Chemistry, Lab of Advanced Materials, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Fudan University , 2205 Songhu Road, Shanghai 200438, P. R. China.
Acc Chem Res. 2017 Apr 18;50(4):895-904. doi: 10.1021/acs.accounts.6b00625. Epub 2017 Mar 10.
Solar energy is the most abundant renewable energy available to the earth and can meet the energy needs of humankind, but efficient conversion of solar energy to electricity is an urgent issue of scientific research. As the third-generation photovoltaic technology, dye-sensitized solar cells (DSSCs) have gained great attention since the landmark efficiency of ∼7% reported by O'Regan and Grätzel. The most attractive features of DSSCs include low cost, simple manufacturing processes, medium-purity materials, and theoretically high power conversion efficiencies. As one of the key materials in DSSCs, the counter electrode (CE) plays a crucial role in completing the electric circuit by catalyzing the reduction of the oxidized state to the reduced state for a redox couple (e.g., I/I) in the electrolyte at the CE-electrolyte interface. To lower the cost caused by the typically used Pt CE, which restricts the large-scale application because of its low reserves and high price, great effort has been made to develop new CE materials alternative to Pt. A lot of Pt-free electrocatalysts, such as carbon materials, inorganic compounds, conductive polymers, and their composites with good electrocatalytic activity, have been applied as CEs in DSSCs in the past years. Metal selenides have been widely used as electrocatalysts for the oxygen reduction reaction and light-harvesting materials for solar cells. Our group first expanded their applications to the DSSC field by using in situ-grown CoSe nanosheet and NiSe nanoparticle films as CEs. This finding has inspired extensive studies on developing new metal selenides in order to seek more efficient CE materials for low-cost DSSCs, and a lot of meaningful results have been achieved in the past years. In this Account, we summarize recent advances in binary and mutinary metal selenides applied as CEs in DSSCs. The synthetic methods for metal selenides with various morphologies and stoichiometric ratios and deposition methods for CE films are described. We emphasize that the in situ growth method exhibits advantages over other methods for fabricating stable and efficient CEs. We focus on the effect of morphology on the electocatalytic and photovoltaic performance. Application of transparent metal selenide CEs in bifacial DSSCs and the superiority of in situ-grown metal selenide nanosheet fiber CEs used for fiber DSSCs are presented. In addition, we show that metal selenides with a hollow sphere structure can function not only as an efficient electrocatalyst but also as a light-scattering layer. Finally, we present our views on the current challenges and future development of metal selenide CE materials.
太阳能是地球上最丰富的可再生能源，可以满足人类的能源需求，但将太阳能高效转化为电能是科学研究的一个紧迫问题。作为第三代光伏技术，染料敏化太阳能电池（DSSC）自 O'Regan 和 Grätzel 报道了约 7%的标志性效率以来，受到了极大的关注。DSSC 的最吸引人的特点包括低成本、简单的制造工艺、中等纯度的材料和理论上的高功率转换效率。作为 DSSC 的关键材料之一，对电极（CE）在通过在 CE-电解质界面处催化氧化态还原到还原态来完成电电路方面起着至关重要的作用，对于在电解质中氧化还原对（例如，I/I）。为了降低通常使用的 Pt CE 造成的成本，Pt CE 的低储量和高价格限制了其大规模应用，因此，人们已经做出了很大的努力来开发替代 Pt 的新型 CE 材料。在过去的几年中，许多无 Pt 的电催化剂，如碳材料、无机化合物、导电聚合物及其与良好电催化活性的复合材料，已被应用于 DSSC 中的 CE。金属硒化物已被广泛用作氧还原反应的电催化剂和太阳能电池的吸光材料。我们的研究小组首先通过使用原位生长的 CoSe 纳米片和 NiSe 纳米颗粒薄膜作为 CE 将它们的应用扩展到 DSSC 领域。这一发现激发了人们对开发新型金属硒化物的广泛研究，以寻求更高效的低成本 DSSC 的 CE 材料，在过去的几年中已经取得了很多有意义的成果。在本报告中，我们总结了近年来作为 DSSC 的 CE 应用的二元和多元金属硒化物的最新进展。描述了各种形态和化学计量比的金属硒化物的合成方法和 CE 薄膜的沉积方法。我们强调，与其他方法相比，原位生长方法在制备稳定和高效的 CE 方面具有优势。我们重点介绍了形态对电催化和光伏性能的影响。介绍了透明金属硒化物 CE 在双面 DSSC 中的应用以及原位生长的金属硒化物纳米片纤维 CE 在纤维 DSSC 中的优越性。此外，我们表明具有空心球结构的金属硒化物不仅可以用作高效电催化剂，还可以用作光散射层。最后，我们提出了对金属硒化物 CE 材料当前挑战和未来发展的看法。
