Optical Characteristics of PCDTBT: PCBM₇₀   Organic Solar Cells

Rashmi Swami* and Sanjay Tiwari

Photonics Research Laboratory, School of Studies in Electronics, Pt. Ravishankar Shukla University, Raipur - 492010

*corresponding Author: rashmi.swami3@gmail.com

[Received 2 April 2014; accepted 21 April 2014]

Abstract.   We herein report on the improved photovoltaic (PV) effects of using a polymer bulk-heterojunction (BHJ) layer that consists of a low-band gap electron donor polymer of poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2 thienyl- 2',l',3'-benzothiadiazole))  (PCDTBT) and an acceptor of  [6,6]-phenyl C70   butyrlc acid methyl ester  (PCBMro).  The characteristics    investigated    include refractive    index, extinction    coefficient,    optical     conductivity, absorbance/transmittance/reflectance and their variation with wavelength, Absorbance/transmittance/reflectance are calculated using extended net radiation method and coding is done in MATLAB. Refractive index, extinction coefficient, absorption coefficient, absorbance of PCDTBT: PCBM70 blend film shows variations in vi"ible range (350 run - 650 nm). Refractive index of PCDTBT: PCBM70increases from wavelength 450 run to 612 nm and  reaches to its maximum value 2.2883 at  610 run wavelength. Extinction coefficient of PCDTBT:PCBM70  has maximum value of 0.4408 at 300 nm wavelength then decreases with increase in wavelength. The PCDTBT:PCBM70 PV showed strong absorption bands and optical conductivity in the visible range from 350 to 650 run, extending to an absorption and conductivity onset at 800 nm, and containing two distinct but broad absorption bands and conductivity band centered at ca. 380-420 run and ca. 475-570 nm. We get high optical conductivity in the region where absorbance of PCDTBT:PCBM70 OSC is high  because  α ). PCDTBT:PC7oBM OSC shows more than 50% transmittance at wavelengths longer than 570 run i.e. transmittance is high in infrared region and  sharp fall below 350 run because of strong absorbance in this region, Reflectance i11  less than 17% in visible and infrared region.

Keywords: bulk heterojunction, organic solar cell, absorbance, transmittance, reflectance

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