Non-thermal phase separation of P3HT and PCBM using polar aprotic solvents for enhancement of photovoltaic performance in bulk heterojunction solar cells
- Non-thermal phase separation of P3HT and PCBM using polar aprotic solvents for enhancement of photovoltaic performance in bulk heterojunction solar cells
- 이지선; 김봉수; 박남규
- Polar aprotic solvent; Valeronitrile; Acetonitrile; Non-thermal phase separation; Bulk heterojunction solar cell; Organic photovoltaics; Solvent-assisted phase separation
- Issue Date
- Synthetic metals
- VOL 176, 26-30
- Additive-assisted non-thermal phase separation of P3HT and PCBM was studied using nitrile solventsthat have low boiling points. 10 volume% of acetonitrile (ACN) or valeronitrile (VN) was added to theP3HT:PCBM blend chlorobezene solution. The P3HT:PCBM bulk heterojunction layer prepared withoutnitrile solvents showed a power conversion efficiency (PCE) of 0.75%. The ACN addition to the blend solu-tion improved the PCE slightly to 1.07% and the VN addition nearly doubled the PCE to 1.40%. The PCEswere mainly enhanced due to the increased photocurrent density. More specifically, the increased crys-tallinity and nanoscale phase separation of P3HT chains and PCBM molecules were key reasons for theimprovement, which were clearly observed in the UV–visible absorption spectroscopy, atomic force spec-troscopy (AFM), and scanning electron microscopy (SEM) experiments. From the normalized UV–visibleabsorption spectra, the addition of ACN and VN into the P3HT:PCBM blend solution made a red-shift ofmain absorption peak from 500 to 510 nm with the appearance of pronounced shoulder peaks at 555and 610 nm. This feature suggested that the interaction between P3HT chains was strengthened withaid of the additives. The main difference between ACN and VN additives was revealed in the AFM andSEM imaging. The VN additive induced to form self-organized 1-dimensional (1D) P3HT domains, whichresulted from the fact that the VN consists of longer alkyl chains and have higher boiling point. Theinteraction between the alkyl chain part in the VN with hexyl chains in the P3HT should promote thenanostructured domain formation of P3HT chains. In addition, the long 1D P3HT domains were web-likely connected, which enabled efficient charge transport in the P3HT:PCBM blend film. Therefore, weconcluded the highest photovoltaic performance of VN-assisted P3HT:PCBM blend devices was achievedby the good phase separation and well-connected transpo
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