Enhanced oxidation power in photoelectrocatalysis based on a micrometer-localized positive potential in a terrace hetero p–n junction

Generally, p–n junction-based solar energy conversion has the disadvantage of a loss in potential gain in comparison with the photon energy. In this study, we found a more positive potential for a lateral domain interface of p–n junction than for a conventional p–n junction. A terrace bilayer (TB) p–n junction of phthalocyanine (H2Pc) and 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (PTCBI) was studied using scanning Kelvin probe microscopy (SKPM), and its electronic properties were analyzed using the contact potential difference (VCPD) data. The analysis of VCPD in the single layer region and the bilayer region (BLR) indicated a vacuum level shift through the electron transfer from PTCBI into indium tin oxide (ITO), from H2Pc into ITO and from H2Pc into PTCBI. Furthermore, the comparison of these VCPD data indicated a micrometer-localized positive potential in the boundary region (BDR) of the terrace bilayer structure of p-type on n-type. The gain difference of the VCPD reached +0.1 V in comparison with the BLR. The phenomena can be explained as a lateral dipole at the p–n junction. Similar phenomena were observed in TB-H2Pc/C60/ITO and TB-H2Pc/PTCBI/Au. The gain was extracted as oxidation power in photoelectrochemistry; i.e., at −0.2 V vs. Ag/AgCl a greater anodic current was observed for a patterned terrace bilayer electrode. Additionally, as a photocatalyst film (i.e., a H2Pc (dot)/PTCBI/PTFE membrane filter), the p–n dot terrace structure showed a higher quantum efficiency (5.1%) than that of the bilayer (3.2%) for the decomposition of acetic acid. The present design and method were utilized to obtain an efficient photocatalyst, especially through the mitigation of potential loss from the photon energy to redox powers without changing the molecular component. A combination of materials that reduces energy loss in organic solar cells has been identified by researchers in Japan. A solar cell comprises two materials: one with excess electrons and one with absent electrons, referred to as holes. An incoming photon can create an electron–hole pair. These separate at the material’s interface and flow in opposite directions to generate a current. Energy is lost as the electric potential difference across the interface is smaller than the energy of the photon. Keiji Nagai and colleagues from the Tokyo Institute of Technology used a technique called scanning Kelvin probe microscopy to investigate this potential difference between two organic materials. They identified a naturally occurring electric potential at this interface, which reduces the potential difference between the materials and thus energy loss during photon conversion. A terrace bilayer (TB) p–n junction of phthalocyanine (H2Pc) and 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (PTCBI) was studied by the use of scanning Kelvin probe microscopy, and its electronic properties was analyzed through the contact potential difference (VCPD) data for single layer region (SLR), bilayer region (BLR), and boundary region (BDR). A micrometer-localized positive potential was found in the BDR of TB of p-type on n-type, which the VCPD value was more +0.1 V than that of the BLR. Both potential gain and the design were utilized for efficient photocatalyst as oxidation power without changing molecular component, just based on the geometrical control.