The Improved Performance Of Dye-sensitized Solar Cells Based On TiO₂ Nanotube Arrays Photoanodes

One-dimensional TiO2 nanotube arrays have been widely used in Dye-Sensitized Solar Cells(DSSCs)owning to its direct pathway for photon-generated carries and excellent photoelectric properties.Large area TiO2 nanotube arrays were successfully prepared on Ti substrates by using two-step anodization,subsequently detached from the Ti substrates and transferred onto the FTO conductive glass to serve as the photoanodes for DSSCs.The highest photovoltaic conversion efficiency(PCE=4.12%)has been achieved in the DSSC assembled with 33-mm-thick and 2.6-3.0 cm2 pure TNT arrays photoanodes area of.In order to improve the photoelectric performance of assembled DSSCs,the photoanodes and counter electrodes of DSSCs have been modifid with various methods as listed below:For the photoanodes:(1)TiO2 nanoparticles were successfully introduced into TiO2 nanotube arrays to form TiO2 nanoparticles/TiO2 nanotube core-shell nanoarrays by traditional TiCl4 treatment.This treatment increases the surface area of the photoanodes siginificantly and accordingly enhances the dye adsorption and light traping,A PCE of 9.02%was achieved in the assembled DSSC with a TiC14-treated TNT photoanode.(2)A sol-gel method was developed to introduce the?20 nm TiO2 nanoparticles into the TiO2 nanotube arrays to form TiO2 nanoparticles/TiO2 nanotube core-shell nanoarrays.The size of the filled TiO2 nanoparticles in TNT arrays is the appropriate dimension in photoanodes of DSSCs to form effective necks between particles,and hence accelerates the electron transfer.Furthermore,such a treatment induces more hydroxyl groups onto the surface of the photoanodes.The chemisorbed hydroxyl groups is especially beneficial for dye adsorption and affects the Jsc and PCE of cells positively.The highest PCE of 9.86%was achieved in DSSC with photoanodes with 2h's TiO2 sol treatment.Based on TiO2-sol treatment results,a thin A12O3 blocking layer was further introduced onto the surface of TiO2 nanoparticles/TiO2 nanotube arrays to form a hierarchical core-shell structure.This metal oxide(A12O3)with a higher conduction band edge can increase the physical separation of injectioned electrons and suppress the recombination of current carriers with the oxidized dye molecules or oxidised redox couple.After coated such a thin A12O3 layer onto the 20 nm TiO2 nanoparticles,the PCE of DSSCs could be improved up to 10.03%(The PCE was 9.86%for DSSCs based on TiO2 nanotube/nanoparticle photoanodes).(3)A water treatment was developed to situ introduce the?15nm TiO2 nanoparticles into TiO2 nanotube arrays at temperature as low as 90?.The PCE 9.6%was achieved for DSSCs based on such a water treated TNT arrays photoanodes.It is of great potential application to improve the PCE of flexible DSSCs due to the flexible transparent conductive film(PET-ITO or PEG-ITO)can keep stable at temperature below 150?For the counter electrodes:Three types of Pt counter electrodes were prepared on FTO conductive glass respectively by magnetron sputtering,thermal decompositing the precursor of H2PtCl6-6H2O solution at high temperature(high-temp)and chemical reduction of H2PtCl6-6H2O solution at low temperature(low-temp).The high light transmittance(60%-83%),low treatment temperature(<100?)and low Pt loading(14.29?g cm-2 per cycle)counter electrodes have been obtained.Based on these three kinds of Pt counter electrodes,a set of dye-sensitized solar cells was assembled with TiO2 nanotube arrays and their PCE were mearsured under different illumination modes.The applicability,advantages and disadvantages of Pt counter electrodes prepared by different methods were compared and analyzed.For DSSCs required front-side illumination,the Pt counter electrodes prepared by thermal decomposition may be optimum because the simple fabrication and high efficiency.An appropriate PCE of 8.6%was abtaind at 5 cycles' spin-coating and thermal annealing.For DSSCs required back-side illumination mode,the Pt counter electrodes prepard by chemical reduction should be the optimum candidate for efficient DSSCs in industrial solar cell application due to the low Pt consumption and high light transmittance.For flexible solar cell application,the Pt electrode prepared by chemical reduction is especially useful due to its low temperature preparation.