Seite - 126 - in Photovoltaic Materials and Electronic Devices

10 For  cells  with  a  finger  grid,  the  cell  efficiency  seems  to  become  less  affected  by  the  cell  length,    as  shown  in  Figure  13,  which  shows  efficiency  as  function  of  the  cell  length  for  illumination  powers  from  0.2  to  1  sun  in  Figure  13a–d.  Note  that  for  each  graph,  the  minimum  value  on  the  x‐axis  is  about  half  of  the  maximum  value  to  facilitate  comparison  with  Figure  12b.    Figure  13.  Efficiency  as  function  of  the  cell  length  for  various  specific  contact  resistances  (Rscr,  in  Ohm  cm2)  for  light  intensity  of:  0.2  sun  (a);  0.5  sun  (b);  0.75  sun  (c);  and  1  sun  (d).  An  additional  observation  is  that  lower  illumination  intensity  reduces  the  impact  of  the  specific  contact  resistance.  In  other  words,  the  expected  impact  of  the  specific  contact  resistance  for  cells  with  metallic  grids  on  the  yearly  yield  of  a  solar  panel  is  less  than  posed  in  Figure  10,  which  was  based  on  an  illumination  power  of  one  sun.  Although  this  suggests  that  the  Rscr  is  a  less  severe  bottleneck,    an  Rscr  below  0.02  Ω  cm2  is  still  highly  recommended.  Figure 13. Efficiency as function of the cell length for various specific contact resistances (Rscr, in Ohm cm2) for light intensity of: 0.2 sun (a); 0.5 sun (b); 0.75 sun (c); and1sun(d). Anadditionalobservationisthatlowerilluminationintensityreducestheimpact of thespecificcontact resistance. Inotherwords, theexpected impactof thespecific contact resistance for cells with metallic grids on the yearly yield of a solar panel is less than posed in Figure 10, which was based on an illumination power of one sun. Although this suggests that the Rscr is a less severe bottleneck, an Rscr below 0.02Ωcm2 is stillhighlyrecommended. 3. ExperimentalSection For theTCOonlycase,wehaveusedfiveTCOswithvarioussheet resistances. Thetransmittance increaseswithsheet resistance,andthisdependsonthespecific TCO and deposition method used. We have used the data shown in Figure 3 to represent theadditionaloptical lossbytheTCOandthevaluesareaimedtoreflect industrialapplicationmethods. For the case of TCO plus metallic grid, a wide range of TCO values were calculated and we present here only data for a TCO sheet resistance of 50Ω/sq. This work only discusses a finger grid configuration, because in previous work, it was determinedthat this is themosteffectivegriddesignformonolithically integrated thin film PV [24]. The material characteristics of the metal in the model consisted 126