Dual Liquid Junction Photoelectrochemistry: Part I. Dual-Cuvette and Dual-Thin-Film Cells for Screening and Quantification of Back-Contact Properties

Abstract

We explore methods for utilizing electrochemical redox contacts both at the front and back of illuminated semiconductors. A dual cuvette cell utilizes a cuvette/gasket/semiconductor/gasket/cuvette sandwich with rapid stirring and the capability for fourelectrode measurements. Results from the dual-cuvette cell include current density-potential (J-E) scans with a cobaltocene +/0 back contact to n-Si(111) and a ferrocene +/0 front contact facing the illumination source, and a logarithmic plot of short-circuit current density vs open-circuit photovoltage for several illumination intensities to quantify the diode ideality factor for this cell. An ITO/liquid/semiconductor/liquid/ITO sandwich in a two-electrode configuration comprises a thin-layer cell. Thin-layer cell results include J-E scans as well as electrochemical impedance/Mott-Schottky analysis of flatband potentials. Results on n-Si(111) electrodes with two liquid junction contacts resemble results from traditional photoelectrochemical cells with a rectifying liquidjunction front contact and a rear metal contact.

Dual Liquid Junction Photoelectrochemistry: Part II. Open-Circuit Photovoltage Variations Due to Surface Chemistry, Interfacial Dipoles, and Non-Ohmic Junctions at Back Contacts

“…This resistive behavior is consistent with previous experiments utilizing a dual-thinlayer photoelectrochemical cell with mild compression, and show only modest improvement with more conductive oxide contacts. 14 Mild compression yielded ∼100 μm-thick liquid layers as opposed to the ∼10-μm-thick liquid layers in more conductive, highly efficient thincell morphologies. 28 Scans acquired under simulated 10 mW cm -2 illumination (not shown) demonstrate higher fill factors and illuminationlimited current density values relative to Fig.…”

“…27 Photoelectrochemical studies utilized a thin-layer cell arrangement described previously in which a semiconductor is sandwiched between two redox liquids that are in turn sandwiched between transparentconductive-oxide-coated glass slides. 14 This cell was located in a glove box with illumination provided by a 300 W ELH-style tungstenhalogen lamp. For the 50-mV-s -1 scans under illumination, the side of the cell that faces the illumination received the counter and reference connections of a potentiostat, while the opposing side received the working and working sense connections.…”

“…Redox solutions alternatively consisted of cobaltocene +/0 , decamethylferrocene +/0 , octamethylferrocene +/0 , dimethylferrocene +/0 , ferrocene +/0 , and acetylferrocene +/0 in propylene carbonate with lithium perchlorate as the supporting electrolyte. 14,28 Vacuum sublimation purified each neutral metallocene species while recrystallization purified each metallocenium salt.…”

“…Dual liquid junction photoelectrochemistry is uniquely positioned to both isolate and quantify the behavior at each contact to a lightabsorbing semiconductor material. 14 Nonaqueous redox couples that demonstrate facile one-electron transfer effectively serve as the ohmic contact to a semiconductor in place of a metal with a comparable work function energy to the Nernstian potential energy of that redox couple. When placed opposing a strongly rectifying redox couple as the other semiconductor contact, variations in the Nernstian solution potential of either redox couple enable studies of contact non-ideality on the resulting solar energy conversion properties.…”