PV conversion of energetic photons of the solar spectrum: Effect of the UV component

The nowadays quite indispensable enhancement of PV conversion efficiency cannot be obtained without new mechanisms. The most useful of these mechanisms has to appear in the front face of the device, i.e. in the emitter, so as to allow exploitation of the energetic photons of the solar spectrum. Such an improvement can be realized through a multistage PV conversion starting by primary generation (photon absorption) followed by secondary generations (hot carrier collisions with low-energy generation centers). This cascade-like process is possible, for example, in multiinterface devices containing several emitter strata. Some of these strata assume the role of primary free-carrier generation while others do the secondary free-carrier generation. We report here investigations of new mechanisms based on I(V) curves measured on test samples with different multiinterface architectures, electronic passivations, front grids, collecting electrodes and so on. The measurements have been performed under a variable intensity incident light beam conserving always its spectral (solar) composition, except for analogous measurement cycles without a UV component. The same beam intensities with a filtered UV component complemented these investigations. The measurements have been compared with those of a weak excitation from a typical halogen lamp (relatively stable flux without a UV component). The test structures show a clear improvement of the PV conversion in the UV range induced by impact ionization within the superficial nanostratum.