Photovoltaic activity of electrodes based on intact photosystem I electrodeposited on bare conducting glass

Abstract

We demonstrate photovoltaic activity of electrodes composed of fluorine-doped tin oxide (FTO) conducting glass and a multilayer of trimeric photosystem I (PSI) from cyanobacterium Synechocystis sp. PCC 6803 yielding, at open circuit potential (OCP) of + 100 mV (vs. SHE), internal quantum efficiency of (0.37 ± 0.11)% and photocurrent density of up to (0.5 ± 0.1) µA/cm 2. The photocurrent measured for OCP is of cathodic nature meaning that preferentially the electrons are injected from the conducting layer of the FTO glass to the photooxidized PSI primary electron donor, P700 + , and further transferred from the photoreduced final electron acceptor of PSI, F b − , via ascorbate electrolyte to the counter electrode. This observation is consistent with preferential donor-side orientation of PSI on FTO imposed by applied electrodeposition. However, by applying high-positive bias (+ 620 mV) to the PSI-FTO electrode, exceeding redox midpoint potential of P700 (+ 450 mV), the photocurrent reverses its orientation and becomes anodic. This is explained by "switching off" the natural photoactivity of PSI particles (by the electrochemical oxidation of P700 to P700 +) and "switching on" the anodic photocurrent from PSI antenna Chls prone to photooxidation at high potentials. The efficient control of the P700 redox state (P700 or P700 +) by external bias applied to the PSI-FTO electrodes was evidenced by ultrafast transient absorption spectroscopy. The advantage of the presented system is its structural simplicity together with in situ-proven high intactness of the PSI particles.

Competition between intra-protein charge recombination and electron transfer outside photosystem I complexes used for photovoltaic applications

“…Next, a positive potential difference (2.5 V) was applied between the conductive surfaces of two electrodes for 5 min. In such previously optimized conditions [16], a preferential migration of PSI particles toward the positive electrode could be observed. After that, the samples were air-dried overnight at 4 °C to evaporate the solvent.…”

“…The immobilization procedure was described in detail in previous works [16,37]. Briefly, 30 µl of dialyzed PSI solution Fig.…”

“…The absorbance of the dried immobilized PSI complexes at the Q y band maximum was measured as A 679nm,1 cm = 0.030 ± 0.005 after correction by subtraction of the FTO glass absorbance. The absorbance of the photoactive biolayer was estimated as originating from ~ 5 monolayers of densely packed PSI complexes [16].…”

“…Photocurrent measurements were performed in a custommade three-electrode photo-electrochemical cell (PEC), as described previously [16]. Briefly, the working electrode (WE) was PSI-FTO glass, the counter electrode (CE) was a platinum wire, and the reference electrode (RE) was Ag/ AgCl filled with 3 M KCl (220 mV vs SHE), connected to the Autolab PGSTAT204 potentiostat.…”

“…Three types of efficiencies are usually reported for solar cell characterization: (1) external efficiency (η = P out /P in ) defined as a ratio of the power of electrical photocurrent (P out ) and the power of incident light (P in ), (2) incident photon to current efficiency (IPCE) or external quantum efficiency (EQE) defined as a ratio of the number of photo-generated electrons to the number of incident photons, and (3) internal quantum efficiency (IQE) defined as a ratio of the number of photo-generated electrons to the number of absorbed photons. For the PSI-based devices, the reported η values never exceed ~ 0.5% ([9]-0.001%, [10]-0.08%, [11]-0.17%, [12]-0.52%), EQE does not exceed 11% ( [12]-5%, [13]-0.01%, [14]-5%, [15]-11%,), whereas IQE does not exceed 39% ([14]-5%, [15]-39%, [16]-0.37%). Only the last parameter can be directly compared to the ~ 100% intrinsic "IQE" value characteristic of the photosynthetic proteins.…”