Efficiency-limiting processes in OPV bulk heterojunctions of GeNIDTBT and IDT-based acceptors
ProgramMaterial Science and Engineering
KAUST DepartmentPhysical Science and Engineering (PSE) Division
Embargo End Date2019-05-28
Permanent link to this recordhttp://hdl.handle.net/10754/627964
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Access RestrictionsAt the time of archiving, the student author of this thesis opted to temporarily restrict access to it. The full text of this thesis became available to the public after the expiration of the embargo on 2019-05-28.
AbstractThe successful realization of highly efficient bulk heterojunction OPV devices requires the development of organic donor and acceptor materials with tailored properties. Recently, non-fullerene acceptors (NFAs) have emerged as an alternative to the ubiquitously used fullerene derivatives. NFAs showed a rapid increase in efficiencies, now exceeding a PCE of 13%. In my thesis research, I used two small molecule IDT-based acceptors, namely O-IDTBR and O-IDTBCN, in combination with a wide bandgap donor polymer, GeNIDT-BT, as active material in BHJ solar cells and investigated their photophysical characteristics. The polymer combined with O-IDTBR as acceptor achieved a power conversion efficiency of only 2%, which is significantly lower than that obtained for the system of GeNIDT-BT: O-IDTBCN (5.3%). Using nano- to microsecond transient absorption spectroscopy, I investigated both systems and demonstrated that GeNIDT-BT:O-IDTBR exhibits more geminate recombination of interfacial charge-transfer states, leading to lower short circuit currents. Using time-delayed collection field experiments, I studied the field dependence of charge generation and its impact on the device fill factor. Overall, my results provide a qualitative understanding of the efficiency-limiting processes in both systems and their impact on device performance.