2970 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com full papers Photosystem I (PSI)/Photosystem II (PSII)-Based Photo-Bioelectrochemical Cells Revealing Directional Generation of Photocurrents Omer Yehezkeli, Ran Tel-Vered, Dorit Michaeli, Rachel Nechushtai, and Itamar Willner* 1. Introduction The assembly of photo-bioelectrochemical cells based on photosynthetic reaction centers, [1] or photoelectrochemical cells, [2,3] attracts growing interest as a means to convert solar light energy into electrical power. Such systems might, also, provide guidelines for the tailoring of biomimetic photo- bioelectrochemical or optoelectronic systems. The construction of photo-bioelectrochemical devices involves several challenges that include the integration of the photosystem proteins with electrodes, the electron transfer wiring of the photosystems with the electrodes, [4] and the effective collection of the light, which are essential to yield high photon-to-electron efficiencies. Layered assemblies of photosystem I, PSI, and/or photosystem II, PSII, on ITO electrodes are constructed using a layer-by-layer deposition process, where poly N,N ′-dibenzyl-4,4′-bipyridinium (poly-benzyl viologen, PBV 2 + ) is used as an inter- protein “glue”. While the layered assembly of PSI generates an anodic photocurrent only in the presence of a sacrificial electron donor system, such as dichlorophenol indophenol (DCPIP)/ascorbate, the PSII-modified electrode leads, upon irradiation, to the formation of an anodic photocurrent (while evolving oxygen), in the absence of any sacrificial component. The photocurrent is generated by transferring the electrons from the PSII units to the PBV 2 + redox polymer. The charge-separated species allow, then, the injection of the electrons to the electrode, with the concomitant evolution of O 2 . A layered assembly, consisting of a PSI layer attached to a layer of PSII by the redox polymer PBV 2 + , leads to an anodic photocurrent that is 2-fold higher, as compared to the anodic photocurrent generated by a PSII-modified electrode. This observation is attributed to an enhanced charge separation in the two-photosystem assembly. By the further nano-engineering of the two photosystems on the electrode using two different redox polymers, vectorial electron transfer to the electrode is demonstrated, resulting in a ca. 6-fold enhancement in the photocurrent. The reversed bi-layer assembly, consisting of a PSII layer linked to a layer of PSI by the PBV 2 + redox polymer, yields, upon irradiation, an inefficient cathodic current. This observation is attributed to a mixture of photoinduced electron transfer reactions of opposing effects on the photocurrent directions in the two-photosystem assembly. Photoelectrochemistry DOI: 10.1002/smll.201300051 O. Yehekeli, Dr. R. Tel-Vered, Prof. I. Willner Institute of Chemistry Minerva Center for Bio-Hybrid Complex Systems The Hebrew University of Jerusalem Jerusalem, 91904, Israel E-mail: willnea@vms.huji.ac.il D. Michaeli, Prof. R. Nechushtai Department of Plant Sciences the Silberman Institute of Life Sciences Minerva Center for Bio-Hybrid Complex Systems The Hebrew University of Jerusalem Jerusalem 91904, Israel small 2013, 9, No. 17, 2970–2978