Seite - 116 - in Photovoltaic Materials and Electronic Devices

2. ResultsandDiscussion 2.1. GeneralConsiderations In thin film solar panels, the panel is usually divided into parallel cells that are series connected. There are several ways to accomplish this and Figure 1 details twoof them.Materials  2016,  9,  96    Figure  1.  Schematic  representations  (not  to  scale)  of  different  interconnection  and  cell  layouts  with  a  side  view  (a,c,e,g)  and  a  top  view  (b,d,f,h).  The  top  image  shows  the  front  contact  (in  green),  the  absorber  material  (in  blue)  and  the  back  contact  (in  grey).  In  addition,  the  separation  and  interconnection  layout  between  two  adjacent  cells  is  shown.  The  surface  area  of  the  TCO/back  contact  material  interface  is  indicated  by  the  white  dashed  box.  The  flow  of  current  is  depicted  by  the  arrows.  The  second  highest  image  shows  the  case  where  the  front  contact  is  supplemented  by  a  metal  grid  (in  orange),  whereas  the  right  image  displays  the  area  covered  by  the  metal  (not  to  scale).  The  third  image  shows  the  case  of  the  metal  interconnect,  for  which  two  material  interfaces  are  important:  the  metal  back  contact  area  represented  by  the  white  dashed  box  and  the  metal/TCO  contact  areas  represented  by  the  blue  dashed  box.    A  modest  cell  efficiency  of  19%  was  chosen,  as  this  has  been  reported  for  different  thin  film  materials  with  various  band  gaps,  which  result  in  different  open  circuit  voltages.  Three  I‐V  curves  were  chosen  with  an  efficiency  of  19%  and  open  circuit  voltages  (Voc)  of  0.7,  0.9  and  1.1  V,  as  to  represent  typical  values  for  thin  film  CIGS,  CdTe  and  perovskite  solar  cells,  respectively.  The  curves  are  shown  in  Figure  2a.  More  details  of  the  IV  curves  can  be  found  in  the  Experimental  Section.    Figure  2.  I‐V  characteristics  used  for  the  study  (a)  cells  of  19%  efficiency  with  different  open  circuit  voltages  (in  V,  see  legend);  and  (b)  cell  with  a  Voc  of  0.7  V  for  different  light  intensities  (see  legend)  in  which  one  sun  is  equivalent  to  1000  W/m2).  For  the  curve  with  a  Voc  of  0.7  V,  the  illumination  intensity  was  varied  and  its  effect  on  the  IV  Figure1. Schematic representations (not toscale)ofdifferent interconnectionand cell layouts with a side view (a,c,e,g) and a top view (b,d,f,h). Th top im ge shows the front contact (in green), the absorber material (in blue) and the back contact (ingrey). Inaddition, theseparationandinterconnection layoutbetween two adjacent cells is shown. The surface area of the TCO/back contact material interface is indicatedbythewhit dash dbox. Theflowofcurrent isdepict dby the arrows. The second highest imag shows the case w re the front contact is supplemented by a metal grid (in orange), whereas the right image displays the area covered by the metal (not to scale). The third image shows the case of the metal interconnect, for which two material interfaces are important: the metal back contactarearepresentedbythewhitedashedboxandthemetal/TCOcontactareas representedbythebluedashedbox. The first is the classic way, in which the TCO is both the front contact and the interconnect (Figure 1a,b). In this case, the isolation area of the back contact is filledwith thesemiconductingabsorbermaterialandall thecurrent is transported through the TCO. The TCO can be enhanced by a metallic finger grid, while the interconnection between top and bottom electrode takes place at the TCO back 116