Effect of insertion of bathocuproine buffer layer at grating-structured cathode–organic-layer interface in bulk-heterojunction solar cells

Masaru Sakomura,Kazuyoshi Ueda,Yuya Yokokura,Yusuke Takagi

doi:10.1063/1.5129351

Abstract

A grating-structured interface of a poly(3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-based bulk-heterojunction (BHJ) photovoltaic (PV) cell was designed and fabricated to obtain a desirable thickness distribution of the deposited bathocuproine (BCP) buffer layer to efficiently utilize its potentials. As a master mold of the grating-structure, a commercially available recordable digital versatile disc (DVD-R) substrate was employed. The grating-structured surface of the P3HT:PCBM layer was successfully produced by duplication from a poly(dimethylsiloxane) secondary mold using the spin cast molding technique. From morphological observations of the grating-structured surface covered with vapor-deposited BCP, we roughly estimated the ratio of the BCP thickness at “walls” to that at “top” and “bottom” regions to be ∼0.5. The grating-type BHJ PV cell with a 5-nm-thick BCP layer exhibited the maximum power-conversion efficiency (ηp) of 3.51%. Compared with the conventional flat-type BHJ PV cell with a 20-nm-thick BCP layer, the performance of the grating-type BHJ PV cell with a 20-nm-thick BCP layer was remarkably improved, owing to the contribution of the wall side contact, which provides a lower-barrier path of the electrons toward the cathode through the thinner BCP layer.

Highlights

Organic photovoltaic (PV) cells have been attracting increased attention owing to their potentials to meet the demands of inexpensive, renewable, and clean energy resources
Over the past decade, the bulk-heterojunction (BHJ) organic PV cells1,2 composed of p-type poly(3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been intensively investigated as one of the most prominent candidates for a polymer PV cell
In contrast to planar-heterojunction (PHJ) architectures,10–14 the interpenetrating networks in the BHJ’s blended active layer of P3HT:PCBM enable a large expansion of the total area of the p-n interface

Summary

Introduction

Organic photovoltaic (PV) cells have been attracting increased attention owing to their potentials to meet the demands of inexpensive, renewable, and clean energy resources. Over the past decade, the bulk-heterojunction (BHJ) organic PV cells composed of p-type poly(3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) have been intensively investigated as one of the most prominent candidates for a polymer PV cell.. In contrast to planar-heterojunction (PHJ) architectures, the interpenetrating networks in the BHJ’s blended active layer of P3HT:PCBM enable a large expansion of the total area of the p-n interface. In order to achieve BHJ PV cells with high performances, the resulting negative and positive carriers should be efficiently collected at the electron-collecting cathode and hole-collecting anode electrodes, respectively. As the carrier collections are significantly affected by the electrical properties at the electrode interfaces, an appropriate choice of the buffer layers, introduced at the blended-polymeractive-layer–cathode and –anode interfaces, is required for highly efficient BHJ PV cells.

Methods

Results

Conclusion