Understanding the Thickness and Light-Intensity Dependent Performance of Green-Solvent Processed Organic Solar Cells

Abstract

For indoor light harvesting, the adjustable band gap of molecular semiconductors is a significant advantage relative to many inorganic photovoltaic technologies. However, several challenges have to be overcome that include processability in nonhalogenated solvents, sufficiently high thicknesses (>250 nm) and high efficiencies at illuminances typically found in indoor environments. Here, we report on the development and application of new methods to quantify and identify performance losses based on thickness- and intensity-dependent current density–voltage measurements. Furthermore, we report on the fabrication of solar cells based on the blend PBDB-T:F-M processed in the nonhalogenated solvent o-xylene. In the low-intensity regime, insufficiently high shunt resistances limit the photovoltaic performance and by analyzing current density voltage–curves for solar cells with various shunt resistances we find that ∼100 kΩ cm2 are required at 200 lux. We provide a unified description of fill factor losses introducing the concept of light-intensity-dependent apparent shunts that originate from incomplete and voltage-dependent charge collection. In experiment and simulation, we show that good fill factors are associated with a photo-shunt inversely scaling with intensity. Intensity regions with photo-shunt resistances close to the dark-shunt resistance are accompanied by severe extraction losses. To better analyze recombination, we perform a careful analysis of the light intensity and thickness dependence of the open-circuit voltage and prove that trap-assisted recombination dominates the recombination losses at low light intensities.

Synergistic Enhancement of Stability and Performance for Perovskite Solar Cells Using Fluorinated Benzoic Acids as Additives

“…We also measure the J-V curves of the devices with different additives under ten different light intensities from 10 to 100 mW cm À2 (Figure S3, Supporting Information). By fitting the V OC results at different light intensities in a logarithmic form through linear regression yields a straight line that is consistent with Equation ( 4) [70] V…”

“…We also measure the J–V curves of the devices with different additives under ten different light intensities from 10 to 100 mW cm −2 (Figure S3, Supporting Information). By fitting the V OC results at different light intensities in a logarithmic form through linear regression yields a straight line that is consistent with Equation () [ 70 ] where V OC denotes the open circuit voltage, n is the ideality factor, k B is the Boltzmann constant, T is the temperature, P is light intensity, and C is an arbitrary constant denoting the y ‐intercept of Equation ().…”

Hole Transporting Bilayers for Efficient Micrometer‐Thick Perovskite Solar Cells

“…This phenomenon is sometimes called a photoshunt and originates from ohmic-looking recombination currents; that is, recombination currents that still depend exponentially on the quasi-Fermi level splitting but linearly on the external voltage. [40,41] Due to their linear dependence on the external voltage, they appear phenomenologically like a shunt. Finally, the FF is also reduced by ideality factors that increase above unity as seen in Equation ( 1).…”

The Thermodynamic Limit of Indoor Photovoltaics Based on Energetically‐Disordered Molecular Semiconductors

“…[14,15] Of these, organic semiconductors are of particular technological-relevance for indoor applications because of the vast palette of materials available and the tunability afforded by synthetic organic chemistry. [16][17][18][19] In recent years, the performance of organic photovoltaics (OPVs) based on combinations of polymeric donors and lowoffset, non-fullerene (small molecule) acceptors (NFAs) has advanced considerably. [20][21][22][23][24][25] OPV materials and device architectures, however, are not yet optimized for indoor applications, due in part to the relative infancy of the field and the lack of established measurement standards.…”

“…[ 14,15 ] Of these, organic semiconductors are of particular technological‐relevance for indoor applications because of the vast palette of materials available and the tunability afforded by synthetic organic chemistry. [ 16–19 ]…”