Masato Shakutsui

Improvement in Polymer Light-Emitting Diode Performance Using Polymer Heterojunction Structure Prepared by Evaporative Spray Deposition from Ultradilute Solution

We successfully demonstrated a significant improvement in polymer light-emitting diode performance by employing a polymer bilayer structure prepared by evaporative spray deposition from ultradilute solution (ESDUS). The bilayer structure consisted of two π-conjugated polymers, where the top layer was deposited from tetrahydrofuran (THF) solution by ESDUS onto the preceding bottom layer composed of the other THF-soluble polymer. The external quantum efficiency (EQE) of the bilayer device is improved markedly in comparison with that of a corresponding single-layer device prepared by conventional spin-coating. Moreover, the EQE of the bilayer device tends to be constant throughout a wide current region, whereas that of single-layer devices increases gradually with current density. These observations indicate that carriers are effectively blocked at the polymer/polymer interface of the bilayer device.

Fabrication of bulk heterojunction photovoltaic cells with controlled distribution of p-n components by evaporative spray deposition using ultradilute solution

A distribution-controlled bulk heterojunction (dc-BHJ) photovoltaic cell where the distribution of an electron donor and acceptor is controlled across the film was fabricated by Evaporative Spray Deposition using Ultradilute Solution (ESDUS) method, which can build a layered structure of polymer semiconductors soluble in a same solvent, and the energy conversion efficiency, PCE, of the dc-BHJ was significantly improved compared with a conventional BHJ cell. The dc-BHJ cells were fabricated by changing the ratio of a donor, regioregular poly(3-hexyl-thiophene-2,5-diyl) (P3HT), and an acceptor, a fullerene derivative (PCBM), from 2:1 to 1:2. The short circuit current, Jsc, and PCE of a dc-BHJ cell having P3HT-rich BHJ/PCBM-rich BHJ structure was 6.06 mA/cm2 and 2.15 %, respectively, while those of a conventional BHJ cell having P3HT:PCBM=1:1 layer were 5.26 mA/cm2, 1.71 %. In the dc-BHJ cells, the introduction of composition gradient brought about the increase in conversion efficiency. The transportation of photogenerated charge carriers to the collecting electrodes was improved because the better pathways should be formed in the dc-BHJ cells.

Bulk-Heterojunction Photovoltaic Cells with Donor?Acceptor Ratio Varied across the Film Prepared by Evaporative Spray Deposition Using Ultradilute Solution Method

We fabricated three types of bulk-heterojunction (BHJ) photovoltaic cells with the electron donor and acceptor ratio varied across the film. One has a stacked layer structure of a donor-rich layer (2:1) the near cathode and an acceptor-rich layer (1:2) near the anode (DA-BHJ), another has a stacked structure with the inverse order (AD-BHJ), and the other has a constant ratio (1:1) as a reference. These were fabricated by evaporative spray deposition using ultradilute solution (ESDUS) method. The DA-BHJ cell showed significantly higher energy conversion efficiency than the AD-BHJ cell and the reference BHJ cell where the three exhibited almost identical light absorption.