ively ▁to ▁the ▁net ▁phot ov olt age . ▁The ▁more ▁popular ▁models ▁used ▁to ▁explain ▁the ▁phot ov olt age ▁are ▁review ed ▁below . ▁ ▁The ▁D ember ▁effect ▁▁ ▁When ▁phot og ener ated ▁electrons ▁and ▁holes ▁have ▁different ▁mob ilities , ▁a ▁potential ▁difference ▁can ▁be ▁created ▁between ▁the ▁ill umin ated ▁and ▁non - ill umin ated ▁faces ▁of ▁a ▁sem icon duct or ▁sl ab . ▁Gener ally ▁this ▁potential ▁is ▁created ▁through ▁the ▁depth ▁of ▁the ▁sl ab , ▁whether ▁it ▁is ▁a ▁bulk ▁sem icon duct or ▁or ▁a ▁pol yc ry st all ine ▁film . ▁The ▁difference ▁between ▁these ▁cases ▁is ▁that ▁in ▁the ▁latter , ▁a ▁phot ov olt age ▁can ▁be ▁created ▁in ▁each ▁one ▁of ▁the ▁micro c ry st all ites . ▁As ▁was ▁mentioned ▁above , ▁in ▁the ▁ob lique ▁de position ▁process ▁incl ined ▁cry st all ites ▁are ▁formed ▁in ▁which ▁one ▁face ▁can ▁abs orb ▁light ▁more ▁than ▁the ▁other . ▁This ▁may ▁cause ▁a ▁phot ov olt age ▁to ▁be ▁generated ▁along ▁the ▁film , ▁as ▁well ▁as ▁through ▁its ▁depth . ▁The ▁transfer ▁of ▁carri ers ▁at ▁the ▁surface ▁of ▁cry st all ites ▁is ▁assumed ▁to ▁be ▁h inder ed ▁by ▁the ▁presence ▁of ▁some ▁un spec ified ▁layer ▁with ▁different ▁properties , ▁thus ▁can cellation ▁of ▁consecutive ▁D ember ▁volt ages ▁is ▁being ▁prevent ed . ▁To ▁explain ▁the ▁polar ity ▁of ▁the ▁P V ▁which ▁is ▁independent ▁of ▁the ▁ill