Organic solar cells

A new look at traditional models

Jonathan D. Servaites, Mark A Ratner, Tobin J Marks

Research output: Contribution to journalArticle

246 Citations (Scopus)

Abstract

Traditional inorganic solar cell models, originating with the work of Shockley, are widely used in understanding bulk heterojunction (BHJ) organic solar cell response (organic solar cells are also referred to as organic photovoltaics, or OPVs). While these models can be useful, there are several key points of departure from traditional solar cell behavior. In this Perspective, we discuss three important areas: (1) geminate pair and bimolecular recombination, (2) effects of interfacial layers inserted between the electrodes and active layer, and (3) resistance effects. Since organic solar cell materials typically have large Coulombic exciton binding energies (e.g., ∼0.3-0.5 eV), limited dissociation of photogenerated charge carriers can be a significant limitation in these cells that is not observed in traditional silicon solar cells. Additionally, the active layer morphology of BHJ organic solar cells allows free charge carriers to recombine before extraction from the cell, creating another photocurrent loss mechanism. Interfacial layers serve a unique role in BHJ organic solar cells; in addition to conventional functions such as photon transmission and charge injection, interfacial layers often act as "blocking" layers, ensuring that charge carriers are collected at their respective electrodes (i.e., electrons at the cathode and holes at the anode). Additionally, resistance effects in organic solar cells differ from traditional models in both field and cell area dependencies. Organic semiconductor mobilities and charge densities exhibit significant sensitivity to field strength, with mobility varying by ∼10x over typical cell voltage test ranges (1 V). This creates the need for alternative models to describe cell internal resistance. Finally, resistance losses are also sensitive to cell area, due to the limited conductivities of the transparent electrode materials used. Therefore, accommodation of the above deviations from traditional models is imperative for the design and synthesis of new generation high efficiency organic solar cell materials.

Original languageEnglish
Pages (from-to)4410-4422
Number of pages13
JournalEnergy and Environmental Science
Volume4
Issue number11
DOIs
Publication statusPublished - Nov 2011

Fingerprint

Charge carriers
Heterojunctions
Electrodes
electrode
Solar cells
active layer
Charge injection
Semiconducting organic compounds
Silicon solar cells
Organic solar cells
solar cell
Charge density
Binding energy
Photocurrents
Excitons
Anodes
Cathodes
Photons
recombination
silicon

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Environmental Chemistry
  • Pollution
  • Nuclear Energy and Engineering

Cite this

Organic solar cells : A new look at traditional models. / Servaites, Jonathan D.; Ratner, Mark A; Marks, Tobin J.

In: Energy and Environmental Science, Vol. 4, No. 11, 11.2011, p. 4410-4422.

Research output: Contribution to journalArticle

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