On the importance of structural disorder and eutectic mixing for organic photovoltaic systems.
Development of state diagrams through advanced thermal analysis

Student thesis: Doctoral Thesis

Abstract

This thesis contributes to a better understanding of the temperature-composition-morphology relationships of mixtures made of electron donor and acceptor materials used in active layers of organic photovoltaic (OPV) devices. To do so, accurate state diagrams (i.e. out of thermodynamic equilibrium) of different conjugated systems were constructed with a focus on both ordered and disordered phases. Three different systems were studied. The state diagram of P3HT:PC61BM (i.e. a conjugated polymer mixed with a fullerene acceptor) was chosen for the initial development of the methodology. A conjugated small molecule (SM) based system was also investigated by RHC combined with solid-state NMR and X-ray diffraction. p-DTS(FBTTh2)2, a SM leading to efficient OPV when mixed with PC71BM, was studied and its state diagram was constructed. Experimental results showed that diiodooctane (DIO), used as a co-solvent during solution processing of p-DTS(FBTTh2)2:PC71BM mixtures, remains in the mixture after deposition and drying. Finally, the effect of homocoupling defects (a side product of the synthesis of p-DTS(FBTTh2)2) on the thermal behaviour was studied by developing the full state diagram of p-DTS(FBTTh2)2:homocoupled p DTS(FBTTh2)2.

Date of Award18 Apr 2018
Original languageEnglish
Awarding Institution
  • Vrije Universiteit Brussel
SupervisorGuy Van Assche (Promotor), Niko Van den Brande (Co-promotor), Wouter Maes (Jury), Eric Nies (Jury), Heidi Ottevaere (Jury), Rik Pintelon (Jury), Hubert Rahier (Jury) & Bruno Van Mele (Advisor)

Keywords

  • organic phoovoltaics
  • phase diagrams
  • state diagrams
  • eutectic diagrams
  • advanced thermal analysis
  • Rapid Heat-Cool DSC (RHC)
  • ultrafast scanning chip nanocalorimetry

Cite this

'