Introduction to Organic Solar Cells - Organic Solar Cells: Materials and Device Physics - page 13

Power conversion efficiency (PCE). Finally, the PCE represents the efficiency
of the solar cell and can be calculated as follows:

PCE ¼ V oc J sc FF
P in

; ð 1 : 3 Þ

where P in is the input power density.

1.5.2 Incident Photon to Electron Conversion Efficiency

J-V characteristics alone are not sufficient to fully characterize a solar cell, as they
do not illustrate optical factors in detail. To further study the efficiency of our solar
cell at each wavelength, the measure of incident photon to electron conversion
efficiency (IPCE) is important. IPCE represents the percentage of incident photons
that are converted to carriers that are finally collected at the electrodes under short
circuit conditions and is equivalent to EQE. Hence, the integration of an IPCE
spectrum is proportional to the short circuit current.
The shape of IPCE curve is highly dependent on the absorption curve of the
active layer. In particular, IPCE is useful evidence when applying techniques to
improve absorption in particular wavelength positions (e.g. using plasmonic
structures) can be reflected as improvements in IPCE at the corresponding
wavelengths. Other than optical effects, electrical effects such as enhanced charge
collection is reflected as shifts of an entire IPCE curve as electrical characteristics
are largely wavelength independent.

1.6 Conclusions

In this chapter, we have briefly described the basics of OSCs. An overview of
organic semiconductors was first provided. The four essential steps of the operation
of solar cells, namely exciton generation, exciton diffusion, exciton dissociation, and
charge collection were explained in detail. Conventional structures of OSCs,
including the bilayer, BHJ and tandem cells, and the basic characterization methods
of OSCs were described. This chapter provides the fundamental knowledge in OSCs
to facilitate understanding of the work provided in the following chapter.

References

1. Akamatu H, Inokuchi H, Matsunaga Y (1954) Electrical conductivity of the perylene bromine
complex. Nature 173(4395):168-169
2. Tang C (1987) Organic electroluminescent diodes. Appl Phys Lett 51(12):913