Interpretation of Optoelectronic Transient and Charge Extraction Measurements in Dye‐Sensitized Solar Cells

Abstract

Tools that assess the limitations of dye sensitized solar cells (DSSCs) made with new materials are critical for progress. Measuring the transient electrical signals (voltage or current) after optically perturbing a DSSC is an approach which can give information about electron concentration, transport and recombination. Here we describe the theory and practice of this class of optoelectronic measurements, illustrated with numerous examples. The measurements are interpreted with the multiple trapping continuum model which describes electrons in a semiconductor with an exponential distribution of trapping states. We review standard small perturbation photocurrent and photovoltage transients, and introduce the photovoltage time of flight measurement which allows the simultaneous derivation of both effective diffusion and recombination coefficients. We then consider the utility of large perturbation measurements such as charge extraction and the current interrupt technique for finding the internal charge and voltage within a device. Combining these measurements allows differences between DSSCs to be understood in terms such as electron collection efficiency, semiconductor conduction band edge shifts and recombination kinetics.

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

“…It was found in both these cell types that the differential charging method gives essentially the same stored charge as the charge extraction method. 31,32,36 We show herein that this is not true for mpTiO 2 /MAPI cells. The differential capacitance can be measured by combining transient photovoltage (TPV) and transient photocurrent (TPC) results to find C = dV/dt / (dQ/dt).…”

“…32 The method measures the voltage that can be generated at OC by the charge that is accumulated at SC (see experimental section for details). Figure 4a compares the current interrupt voltage transient from two similar J sc s, for 5 and 60 second sTEBBing at SC.…”

Unravelling the Potential for Dithienopyrrole Sensitizers in Dye-Sensitized Solar Cells

“…These variations may be related to fluctuation in the electron density and/or shifts in the conduction band edge of the TiO 2 . 30 Using transient photocurrent decay measurements, we studied the electron lifetime and capacitance as a function of voltage ( Figure 5). The lifetime of electrons injected in the TiO 2 (τ n ) is shorter for LP227 compared to LP225.…”

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

“…This picture involves trap states which do not act as fast recombination centers (similar to dye sensitized solar cells). [49] We hypothesize that these traps may be present in MAI-rich regions surrounding the perovskite grains. These would inhibit electronic charge transport in MAI-excess devices, resulting in decreased collection efficiency and explaining the lower Jsc measured for these devices.…”