Study of Nano-Filtration and Solvent Effects for Improving Efficacy of Organic Photovoltaic

Conductive polymer such as poly (3,4-ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT:PSS) plays an important role for improving performance of organic photovoltaics (OPVs).

In this study, we investigated the effect of filtrating the buffer layer between the indium tin oxide (ITO) and bulk heterojunction (BHJ); poly(3-hexylthiophene) and [6,6]-phenylC71 butyric acid methyl ester (P3HT:PC71BM) used in our organic photovoltaics (OPVs) as shown in Figure 1.

This buffer layer consists of poly (3,4-ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT:PSS) doping with different solvents [isopropyl alcohol (IPA), ethanol, and methanol]. For comparison, we also studied the OPV devices without filtering the buffer layers.

The OPV devices fabricated with filtered buffer layer show better performance than OPV devices without buffer layer filtration.  The OPV devices with buffer layers; PEDOT:PSS/IPA, PEDOT:PSS/Ethanol, and PEDOT:PSS/Methanol after filtration showed 24 %, 16 %, and 11 % improvement in short circuit current density (Jsc) , respectively compared to the same OPV devices without filtration. The maximum exciton generation rates (Gmax), and the exciton dissociation probabilities [P (E, T)] were calculated for all fabricated OPV devices to explain the performance enhancement.

The data showed that the performance enhancement of OPVs devices after filtering the buffer layers originate from the large increase of Jsc.  Filtering the buffer layers enhanced light absorption of BHJs, increased the surface roughness, and decreased the sheet resistance of buffer layer after filtration.

Figure 1. A schematic diagram of ITO/PEDOT:PSS:different organic solvents/P3HT: PC71BM/Al