[Paper Review] From Dye Sensitized to Perovskite Solar Cells, The Missing Link

So‐Min Yoo, Seog Joon Yoon+4 more|arXiv (Cornell University)|May 28, 2019

Perovskite Materials and Applications1 references38 citations

TL;DR

The paper links dye-sensitized solar cell impedance patterns to perovskite solar cells by controlling precursor concentration, and provides an equivalent circuit model to interpret PSC impedance in terms of transport and recombination processes.

ABSTRACT

Fundamental working mechanisms of perovskite solar cells remain an elusive topic of research. Impedance Spectroscopy (IS) application to perovskite-based devices generates uncommon features and misleading outputs, mainly due to the lack of a stablished model for the interpretation of the results. In this work we control the perovskite precursor concentration to fabricate a series of perovskite-based solar cells with different amounts of perovskite absorber. Low concentration devices present the well-known dye sensitized solar cell (DSSCs) impedance pattern. As the amount of perovskite is increased, the characteristic impedance spectra of thin-film perovskite solar cells (PSCs) arises. This transition is characterized by a change in the working principles, determined by an evolution of the dominant capacitance: from the intermediate frequency chemical capacitance of TiO2 in devices with isolated perovskite domains, to a large low-frequency capacitance signal which divides the spectra in two sections, yet with no direct influence in final device performance. This study allows to link experimentally, in terms of impedance behavior, PSCs with the rest of solar cell devices via DSSCs. We observe that it is not possible to assign a single physical origin to the different resistances determined in the impedance spectra except for the series resistance. In contrast, resistive element present contributions from different physical processes, observing a transport-recombination coupling. Based on this analysis we provide an equivalent circuit model to evaluate the impedance pattern of PSCs in terms of the processes directly affecting the final performance (i.e. considering transport-related and recombination-related losses), a crucial tool for further development of perovskite photovoltaics.

Motivation & Objective

• Investigate fundamental working mechanisms of perovskite solar cells through impedance spectroscopy (IS).
• Explore how changing perovskite precursor concentration alters device impedance patterns.
• Develop an equivalent circuit model that maps impedance features to transport and recombination processes affecting PSC performance.

Proposed method

• Fabricate a series of perovskite solar cells with varying amounts of perovskite absorber by controlling precursor concentration.
• Measure impedance spectra of the devices to observe transitions from DSSC-like patterns to PSC patterns.
• Analyze how dominant capacitance evolves from TiO2 chemical capacitance to a large low-frequency capacitance with increased perovskite content.
• Propose an equivalent circuit model that separates transport-related and recombination-related losses in the impedance response.

Experimental results

Research questions

• RQ1 How does perovskite precursor concentration influence the impedance spectra of solar cells?
• RQ2 Can PSC impedance be interpreted with a unified model across DSSC-like and PSC regimes?
• RQ3 What are the physical origins of the resistive elements in PSC impedance spectra beyond the series resistance?
• RQ4 How do transport and recombination processes manifest in impedance measurements and relate to final device performance?

Key findings

• Low-perovskite-concentration devices display DSSC-like impedance patterns.
• Increasing perovskite content switches the spectra to characteristic PSC patterns with a large low-frequency capacitance.
• The dominant capacitance evolves from TiO2-related chemical capacitance to a large low-frequency signal that divides the spectra into two sections but does not directly govern final performance.
• Resistive elements cannot be assigned a single physical origin other than series resistance; they reflect combined transport and recombination contributions.
• An equivalent circuit model is provided to evaluate impedance in terms of transport-related and recombination-related losses.