Page - 166 - in Photovoltaic Materials and Electronic Devices

dye at room temperature for 2 h. A sandwich-type configuration was used to measure the presentation of the DSSCs. An active area of 1 cm2 was assembled by using a Pt-coated AZO substrate as a counter electrode, and the Pt/AZO was heatedat200˝Cfor30mininair. TheDSSCwassealedemployingapolymerresin (Surlyn) to act as a spacer. The electrolyte was injected into the space among the electrodes from these two holes, and then these two holes were sealed completely by using Surlyn. The electrolyte (0.5 M 4-tert-butyl-pyridine + 0.05 M I2 + 0.5 M LiI + 0.6 M tetrabutylammonium iodide) was injected to the cell and then sealed with UV gel. The influence of growth time on the structural and optical properties of these ZnO NRs was analyzed by XRD and UV-visible spectrophotometry. Surface morphologies of the ZnO nanorods were examined using field-emission scanning electron microscope (FESEM). The photocurrent-voltage (I-V) characteristic curves weremeasuredusingKeithley2420underAM1.5illumination. Theelectrochemical impedance spectroscopy (EIS) was measured under the light illumination of AM 1.5 G (100 mW/cm2) with an impedance analyzer (Autolab PGSTAT 30) (Metrohm Autolab, Utrecht, Netherlands) when a device was applied with its open-circuit voltage (Voc). An additional alternative sinusoidal voltage amplitude 10 mV was also applied between an anode and a cathode of a device over the frequency range of 0.02~100 kHz. The external quantum efficiency (EQE) results were acquired from a system using a 300 W xenon lamp (Newport 66984) light source and a monochromator (Newport 74112) (Newport Corporation, Taipei, Taiwan). The beam spot size at the sample measured was approximately 1 mmˆ 3 mm. The temperaturewascontrolledat25˝Cduringthemeasurements. heat After  the  reaction  was  complete,  the  resulting  ZnO  NRs  were  rinsed  with  deionized  water  to  remove  residual  ZnO  particles  and  impurities.  A  D‐719  dye,  cis‐bis(isothiocyanato)bis(2,2′‐bipyridyl‐ 4,4′‐dicarboxylato)  ruthenium(II)bis‐tetrabutylammonium,  (Everlight  Chemical  Industrial  Corp.,  Taipei,  Taiwan)  was  dissolved  in  acetonitrile  for  preparing  a  0.5  mM  dye  solution.  Dye  sensitization  was  propagated  by  soaking  the  ZnO  photoelectrodes  in  he  D‐719  dye  at  room  temperature  for  2  h.  A  sandwich‐type  configuration  was  u ed  o  measure  th   presentatio   of  the  DSSCs.  An  active  area  of  1  cm2  was  assembled  by  using  a  Pt‐coated  AZO  substrate  as  a  counter  electrode,  and  the  Pt/AZO  was  heated  at  200  °C  for  30  min  in  air.  The  DSSC  was  sealed  employing  a  polymer  resin  (Surlyn)  to  act  as  a  spacer.  The  electrolyte  was  injected  into  the  space  among  the  electrodes  from  these  two  holes,  and  then  these  two  holes  were  sealed  completely  by  using  Surlyn.  The  electrolyte  (0.5  M  4‐tert‐butyl‐ pyridine  +  0.05  M  I2  +  0.5  M  LiI  +  0.6  M  tetrabutylammonium  iodide)  was  injected  to  the  cell  and  then  sealed  with  UV  gel.  The  influence  of  growth  time  on  the  structural  and  optical  properties  of  these  ZnO  NRs  was  analyzed  by  XRD  and  UV‐visible  spectrophotometry.  Surface  morphologies  of  the  ZnO  nanorods  were  examined  using  field‐emission  scanning  electron  microscope  (FESEM).  The  photocurrent‐voltage  (I‐V)  characteristic  curves  were  meas red  usi g  K ithley  2420  under  AM  1.5  illumination.  Th   electrochemical  impedance  spectroscopy  (EIS)  was  easured  under  the  light  illumination  of  AM  1.5  G  (100  mW/cm2)  with  an  impedance  analyzer  (Autolab  PGSTAT  30)  (Metrohm  Autolab,  Utrecht,  Netherlands)  when  a  device  was  applied  with  its  open‐circuit  voltage  (Voc).  An  additional  alternative  sinusoidal  voltage  amplitude  10  mV  was  also  applied  between  an  anode  and  a  cathode  of  a  device  over  the  frequency  range  of  0.02~100  kHz.  The  external  quantum  efficiency  (EQE)  results  were  acquired  from  a  system  using  a  300  W  xenon  lamp  (Newport  66984)  light  source  and  a  monochromator  (Newport  74112)  (Newport  Corporation,  Taipei,  Taiwan).  The  beam  spot  size  at  the  sample  measured  was  approximately  1  mm  ×  3  mm.  The  temperature  was  controlled  at  25  °C  during  the  measurements.    Figure  1.  The  schematic  illustrations  of  DSSCs  with  ZnO  nanorods.  3.  Results  and  Discussion  In  this  study,  ZnO  NRs  with  various  lengths  were  grown  on  AZO  substrates  of  photoanodes  to  increase  the  optical  absorption  of  the  dye.  Figure  2a  shows  the  respective  XRD  patterns  for  the  ZnO  NRs  derived  from  the  9‐,  18‐,  and  27‐h  reactions,  respectively.  The  crystalline  structure  was  analyzed  using  XRD  measurements  according  to  a  θ/2θ  configuration.  In  principle,  the  XRD  spectra  indicate  that  the  ZnO  films  developed  without  the  presence  of  secondary  phases  or  groups.  All  the  samples  have  a  hexagonal  wurtzite  structure  of  ZnO  and  grew  along  the  c‐axis;  this  enabled  the  observation  of  the  ZnO  (002)  diffraction  plane  in  the  XRD  pattern.  The  increase  in  intensity  of  the  diffraction  peak  and  also  the  narrowing  of  the  peak,  in  other  words,  decrease  in  the  full  width  at  half  maximum  (FWHM)  of  the  peak,  with  the  length  of  ZnO  NRs  increased,  and  the  crystallinity  improvement  of  the  ZnO  NRs.  Existing  dye  uptake  measurements  were  based  on  dye  desorption  from  the  photoanode  Figure1. Theschematic illustrationsof s ithZnOnanor ds. 3. Res lt andDiscussion In this study, ZnO NRs with various lengths ere grown on AZO substrates of photoanodes to increase the optical absorption of the dye. Figure 2a shows the respective XRD patterns for the ZnO NRs derived from the 9-, 18-, and 27-h reactions, respectively. The crystalline structure was analyzed using XRD 166