Phase Diagram of P3HT/PCBM Blends and Its Implication for the Stability of Morphology

Abstract

In this work, the phase diagram of poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends is measured by means of standard and modulated temperature differential scanning calorimetry. Blends were made by solvent-casting from chlorobenzene, as blends cast from toluene or 1,2-dichlorobenzene prove to retain effects of phase segregation during casting, hindering the determination of the phase diagram. The film morphology of P3HT/PCBM blends cast from chlorobenzene results from a dual crystallization behavior, in which the crystallization of each component is hindered by the other component. A single glass transition is observed for all compositions. The glass transition temperature (Tg) increases with increasing concentration of PCBM: from 12.1 degrees C for pure P3HT to 131.2 degrees C for pure PCBM. The observed Tg defines the operating window for the thermal annealing and explains the long-term instability of both the morphology and the photovoltaic performance of the P3HT/PCBM solar cells.

Soluble fullerene derivatives: The effect of electronic structure on transistor performance and air stability

“…Previous DSC analysis of [60]PCBM obtained identical features in the first cooling and second heating cycles. 40 In comparison, both bis-PCBM and Ketolactam-1 seem to feature a significantly lower degree of crystallinity, below the DSC detection limit (< 10%). As an isomeric mixture, films of bis-PCBM are expected to be non-crystalline.…”

Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

“…This result could be due to the combination of chemical structure and relatively low molecular weight of the materials (reported in Supporting Information Table S1), indeed it has been reported that the Tg of P3HT with low molecular weight, is situated at temperatures as low as 12ºC [52]. Despite the difficult of the DSC measurement interpretation on the pure polymer, it is necessary to consider that after blending with fullerene molecules Tg values might change dramatically [53] by effect of restructuring. Therefore, device thermal stability not only depends on the polymer properties but also on the rest of constituents as discussed in the Introduction.…”

Block copolymer strategies for solar cell technology

“…50,51 This process is extremely sensitive to the solvent used, 52,53 variations in composition, 54 annealing, [55][56][57][58][59] chemical-structure variations, [60][61][62][63] purities, 64 and processing conditions, 65 to name but a few of the related parameters when dealing with what is a fundamentally unstable system. 66 The seminal work by Yang et al demonstrated the necessity of controlled mixing of the acceptor and donor in the composite. Crystalline zones transport charges away from their point of formation, which often occurs in amorphous zones where the donor and acceptor are more closely intermingled.…”