Morphology, structure, and photovoltaic properties of poly(3‐hexylthiophene) and [6,6]‐phenyl‐C61‐butyric acid methyl ester‐based ternary blends doping with polystyrene of different tacticities

Abstract

The influence of the polystyrene of different tacticities on the morphology, phase structure, and photovoltaic properties of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend has been extensively investigated. The atactic polystyrene (aPS) immiscible with P3HT tended to form the phase-separated and columnar structure at low aPS weight ratio. Besides, the aPS could migrate to the surface of the films with PCBM phase distributing in the interfaces between P3HT and aPS domains at high aPS weight ratio of 75 wt %. The syndiotactic polystyrene (sPS) immiscible with P3HT could induce the crystallization of P3HT at low weight ratio of 3 wt %. The device based on aPS/P3HT/PCBM ternary blend showed of power conversion efficiency (PCE) of 1.2% even at aPS weight ratio of 50 wt %. However, the device based on sPS/P3HT/PCBM exhibited a sharp decrease in PCE value from 2.3% to 0.6% at sPS weight ratio of 3 wt %, due to the change in film morphology. The performance of the solar cell is believed to be determined by the morphology and phase structure of the ternary blends as revealed by the atomic force microscopy and UV-vis spectra analysis.

Use of gas cluster ion source depth profiling to study the oxidation of fullerene thin films by XPS

“…Data analysis is further complicated by the presence of other potentially unstable donors that can degrade alongside the PC 61 BM material of interest, which generates a need for a stable partner material in order to isolate the role of oxidation of PCBM from other components in the device. Several authors have noted that PC 61 BM and polystyrene (PS) are readily miscible [42,43] with the addition of PS aiding the formation of stable films, modification of crystal domains [44], simplification of processing [45], or even inclusion in devices to modify morphology [46]. Indeed, additions of PS to PC 61 BM films are being considered as an advantageous development in their own right for perovskite type solar cells, where the improved quality of the film results in open circuit voltage improvements to the finished device [47].…”

“…No O(1s) signal is observed at all for PS below the top surface with only a minor increase in O(1s) signal for PC 61 BM to 3.9 ± 0.5 At% below the top surface, which suggests that the PS-PC 61 BM blended film is less stable than either PS or PC 61 BM individually. Pristine PC 61 BM films have previously been observed to form aggregated clusters which shrink in size when blended with PS, and also that some PC 61 BM clusters are entrapped within polystyrene composites [42,46] which would provide additional interfaces that could be attacked. The extremely complex and extended interfaces formed between different domains in the polymer blends typically used in OPV devices offer a ready potential pathway for oxygen (and nitrogen) ingress into blended films that is not available to either pure material.…”

Addition of P3HT-grafted Silica nanoparticles improves bulk-heterojunction morphology in P3HT-PCBM blends

“…This structure provides high interfacial area for charge transport but lowers the crystallinity of PCBM. It has also been reported that addition of syndiotactic polystyrene can further enhance the efficiency by increasing the crystallization of P3HT 45 . BHJs prepared by grafting P3HT on to the surface of PCBM have shown to improve the thermal stability of the system and obtain domain sizes of around 5 nm.…”