染料敏化太阳能电池SnO_(2)光阳极研究进展

Development on SnO_(2) Photoanodes for Dye-sensitized Solar Cells

染料敏化太阳能电池(DSSCs)由于其成本低、原材料丰富、光电转化效率高等优点,成为新能源开发利用领域研究的热点。光阳极是DSSC的重要组成部分,对提高DSSC的光电转化效率具有重要意义。基于此,首先介绍了SnO_(2)DSSC的工作原理,并分析了效率的影响因素,接着重点讨论了SnO_(2)光阳极的结构设计,在此基础上阐述了光阳极改进(表面包覆或复合、元素掺杂)的研究现状,最后总结规律并对未来的发展趋势和前景进行展望。

In the increasing severe energy crisis,the use of solar energy to replace traditional fossil fuels becomes a consensus in worldwide due to the non-renewable nature of fossil fuels and the inability of new energy sources such as hydrogen,wind,and nuclear energy.Among the forms of solar energy utilization,dye-sensitized solar cells(DSSCs)are a research hotspot in energy development and utilization due to their low cost,abundant raw materials,high efficiency,and long service life.The photoanode is an important component of DSSCs and plays a significant role in improving the photoelectric conversion efficiency of DSSCs.In recent years,various materials and modification methods for dye-sensitized solar cells are applied to design the photoanodes for the improvement of their photoelectric conversion efficiency.Among various photoanode materials,SnO_(2) is an ideal candidate due to its higher electron mobility(i.e.,about 125 cm^(2)·V^(-1)·s^(-1))and larger bandgap width(i.e.,3.5 eV).However,SnO_(2)-based dye-sensitized cells still have two main challenges,i.e.,the lower open-circuit voltage(Voc)(Compared to TiO_(2),the conduction band edge of SnO_(2) shifts positively by up to 300 mV,resulting in a reduced difference between the conduction band potential and the redox potential of the electrolyte);and the lower current density(The isoelectric point of SnO_(2) is smaller,which reduces the binding force between SnO_(2) and acidic photosensitive dyes,leading to a decrease in dye adsorption and thus limiting the increase in current density from the source).This review represented recent research progress on tin SnO_(2) photoanodes in DSSCs,emphasizing the potential application of SnO_(2) in DSSCs and the challenges.This review introduced the structure and working principle of SnO_(2)-based DSSCs,and analyzed the key factors affecting the photoelectric conversion efficiency,including short-circuit current density(JSC),VOC,and fill factor(FF).This review discussed the factors influencing these parameters and focused on the current state of research on improving SnO_(2) photoanodes,with the methods including surface coating,composite construction,ion doping,and metal doping.Although various modification methods are developed to improve the performance of SnO_(2) photoanodes,the overall photoelectric conversion efficiency is still lower,restricting its widespread application in a large scale.Therefore,developing more advanced modification techniques is a necessity to further enhance the performance of SnO_(2)(i.e.,its stability and recyclability),and facilitate its wide application in the energy field,thus providing an effective solution to alleviate the energy crisis.Summary and prospects SnO_(2)-based DSSCs have a potential to replace TiO_(2) DSSCs due to their outstanding charge transport capabilities and stable optical properties.However,a lower conduction band position of pure SnO_(2) makes it difficult to achieve an VOC beyond 500 mV.Also,the lower isoelectric point limits dye adsorption,inherently reducing the JSC.To address the poor performance of SnO_(2) nanoparticles,modifications such as changing their structural morphology,surface coating,and ion doping can be employed to enhance charge transport and suppress charge recombination,significantly improving the photoelectric conversion efficiency of SnO_(2) cells.To date,the photoelectric conversion efficiency of cells based on pure SnO_(2) is 8.74%,while that of SnO_(2)–TiO_(2) composite cells is 9.53%.Although these are significant breakthroughs,there is still a gap,compared to TiO_(2) cells(i.e.,13%).It is evident that the current density of SnO_(2) is able to reach a high level(i.e.,greater than 20 mA·cm–2)due to the good transport performance of SnO_(2),compared to that of TiO_(2),but there is still some gaps in open-circuit voltage and fill factor.Future research aspects are as follows:1)There is a great need for a deep understanding of electron generation,transport,loss,and collection within DSSCs,but many issues remain to be resolved.For instance,the recombination mechanism of photo-generated electrons with I3-is still unclear.The complex internal electron transport process has yet to be fully explained by any model,especially under certain light intensity disturbances affecting photo-generated current and voltage(IMPS/IMVS),necessitating further detailed theoretical studies.There are many possibilities for the process of electron injection from the semiconductor film to the FTO interface,such as thermal emission and tunneling,and there is currently no suitable theory to describe this interface,requiring a further research.2)The further use of transition metals with radii that are similar to Sn4+(such as Ti4+,W4+,and In3+)or the synergistic effect of co-doping metals can be explored to specifically improve various properties of SnO_(2).3)To further break through the photoelectric conversion efficiency of SnO_(2),it is necessary to investigate the working process of DSSCs from a microscopic perspective and optimize each part to identify the processes limiting electron transport,improve electron yield,enhance electron transport processes,and reduce electron loss,aiming to achieve the optimum photoelectric conversion efficiency.