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Real-Time Investigation of Crystallization and Phase-Segregation Dynamics in P3HT:PCBM Solar Cells During Thermal Annealing

DOI: 10.1002/adfm.201002076 DOI Help

Authors: Tiziano Agostinelli (Imperial College London) , Samuele Lilliu (Cardiff University) , John Labram (Imperial College London) , Mariano Campoy-quiles (Institut de Ciència de Materials de Barcelona) , Mark Hampton (University of Cardiff) , Ellis Pires (University of Cardiff) , Jonathan Rawle (Diamond Light Source) , Oier Bikondoa (ESRF) , Donal D. C. Bradley (Imperial College London) , Thomas D. Anthopoulos (University of Strathclyde) , Jenny Nelson (Imperial College London) , J. Emyr Macdonald (Cardiff University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Advanced Functional Materials

State: Published (Approved)
Published: March 2011

Abstract: Crystallization and phase segregation during thermal annealing lead to the increase of power-conversion efficiency in poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk-heterojunction solar cells. An understanding of the length and time scale on which crystallization and phase segregation occur is important to improve control of the nanomorphology. Crystallization is monitored by means of grazing incidence X-ray diffraction in real time during thermal annealing. Furthermore, the change in film density is monitored by means of ellipsometry and the evolution of carrier mobilities by means of field effect transistors, both during annealing. From the combination of such measurements with those of device performance as a function of annealing time, it is concluded that the evolution of microstructure involves two important time windows: i) A first one of about 5 minutes duration wherein crystallization of the polymer correlates with a major increase of photocurrent; ii) a second window of about 30 minutes during which the aggregation of PCBM continues, accompanied by an increase in the fill factor.

Journal Keywords: Conjugated Polymers; Electronic Processes; Microstructures; Solar Cells; Thin Films

Subject Areas: Materials


Instruments: I07-Surface & interface diffraction