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 solvento-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 cm2are 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.