Greenhouse Effect to Enhance Photovoltaic Conversion Efficiency above the Detailed Balance Limit

We investigate the photovoltaic (PV) converter with potential efficiencies beyond the Shockley – Queisser limit. The device comprises a semiconductor n-p junction PV cell placed between a front surface “greenhouse” filter and a back surface mirror. The filter traps long wavelength photons and establishes the photonic bandgap above the semiconductor bandgap. Fast photoelectron relaxation due electron-holes energy transfer and effective trapping of long wavelength photons reduce the population of photoelectrons above the photonic bandgap and increase the population of photoelectrons accumulated above the semiconductor bandgap. This nonequilibrium operating regime is described by increased chemical potential of low energy photoelectrons and reduced chemical potential of high energy photoelectrons. In this way the device provides the reduced emission and enhanced conversion. We present the device design, material optimization, and PV characteristics. The device operation is also discussed in terms of endoreversible thermodynamics.