The Investigation Of Charge Carrier Dynamics In Polymer Solar Cells

In the past ten to fifteen years,many electronic and optoelectronic devices consisting of almost all organic polymeric materials have been demonstrated.The determination of the charge transport properties of organic semiconductors is important toward developing optoelectronic devices.Herein,my master's thesis focuses on the dynamic characteristics of charge carrier transportation of the organic semiconductors devices with the active layer of pure P3 HT and P3HT:PC61BM,and the photoelectric device with the active layer of PDPP-F/PC61 BM and PDPP-F/PC71 BM heterojunction.First,the charge carrier transportation of P3HT:PC61BM blend film has been investigated by using time-of-flight(TOF)method.The carrier mobility is strongly dependent on the photoexcitation density,the applied voltage,the PC61 BM composition.The results show that the change of excitation intensity will lead to the difference of photo-generated charge carrier concentration,and the carrier mobility will decrease with the increase of carrier concentration.The charge carrier mobility has an electric field depending behavior that decreases with the increasing of the applied electric field.The doping of PC61 BM will promote the dissociationof excitons which lead to the increasing of the carrier mobility.The charge carrier transportation of PDPPP-F/PC61 BM and PDPP-F/PC71 BM heterojunction devices has been investigated by using photo-carrier extraction by linearly increasing voltage(photo-CELIV)method.The carrier mobility is strongly dependent on the photoexcitation density,the applied voltage,the delay time,the type and doping ratio of electron acceptors.In general,when the delay time is constant,the mobility in all samples increases with the increasing of carrier concentration.Under the same electron acceptor conditions,with the increase of the concentration of fullerenes,the mobility of the photo-generated carriers in the heterojunction becomes higher.When the doping ratio of the acceptor is the same,the use of PC71 BM as electron acceptor could play a more positive role in enhancement of electrical performance than PC61 BM did.With the increase of the applied electric field,the mobility of all the samples increases,and the recombination life gradually becomes shorter,which indicates that the transport process of the charge carriers has the characteristics of electric field dependence.Finally,we found that the mobility of all samples decreased with the increase of the delay time at the fixed voltage,and the high doping ratio of fullerene will weaken the change of the mobility caused by the delay time.