Below Band-Gap IR Response of Substrate-Free GaAs Solar Cells Using Two-Photon Up-Conversion

Abstract

We have developed a device based upon the concept of two-photon up-conversion to use a part of the IR photons otherwise lost by transparency in a GaAs cell. An ultra thin GaAs cell has been fabricated using the technique of epitaxial lift-off (ELO). This thin cell is placed on top of a 100 µ m thick vitroceramic doped with Yb3+ and Er3+. The two photon upconversion process involved here is based on sequential absorption and energy transfer of two IR photons from Yb3+ to Er3+, which then emit one photon in the green. This green light then produces a photoresponse in the GaAs cell. This cell coupled to the vitroceramic was lighted by an Ti-sapphire IR laser at 1.391 eV, a photon energy below the band gap of GaAs, with an input power able to reach ∼1 W. The GaAs cell photoresponse increases quadratically with the input excitation. For an input excitation of 1 W at 1.39 eV on a 0.039 cm2 substrate-free GaAs cell, the measured efficiency was 2.5%.

Photochemical upconversion: present status and prospects for its application to solar energy conversion

“…One of the most efficient UC phosphors to date is NaYF 4 , doped with Er 3+ or co-doped with Yb 3+ and Er 3+ , which was introduced in 1972 by Menyuk et al 74 Comprehensive reviews of ETU by f -shell ions in solid bulk matrices and nanoparticles include the works by Auzel 11 and Haase et al 75 The first realization of an upconversion-assisted solar cell was based on Yb 3+ and Er 3+ ions in a vitroceramic host, placed behind a GaAs solar cell. 76 The first application of the same system to c-Si solar cells was demonstrated in 2005 by Shalav et al, 13,77 and current lanthanoid-based upconversion efforts are mainly focused around crystalline silicon, 14,[78][79][80] due to the energetically favorable absorption of Er 3+ around 1523 nm, below the c-Si band edge in energy and within a local maximum of the solar spectral irradiance. 12 Currently, the most efficient lanthanoid upconversion phosphor for c-Si PV applications appears to be β -NaYF 4 :20-25%Er 3+ powder.…”

Influence of metallic nanoparticles on upconversion processes

“…Potential applications include lasers, 1 three dimensional imaging, 2 quantum counters, 3 or photovoltaic cells. [4][5][6][7][8] A usual path to maximize the upconversion emission efficiency consists in trying different combinations of host matrices and rare-earth atoms. The crystal field from the host influences the transition probabilities between the rare-earth levels in a manner very dependent on the microscopic details of the quantum charge distributions.…”

The quest for very high efficiency in Photovoltaic energy conversion

“…At higher concentration factors, the focal point would have a higher radiation temperature than the source, which is thermodynamically impossible. 4 If not, one could reversibly transport heat of a cold body towards a hot body, and we would have a perpetual motion machine. In a traditional device, the photons whose energy conversion is most effective are those whose energy is just above the threshold of absorption (energy gap E g ).…”

“…In the approach'photon addition' , the photons whose energy is too weak to be used directly by a photodiode could be converted by nonlinear optics into a lower number of photons of larger energy. e main results on this topic have been obtained with materials in which infrared radiation is absorbed by several ions of a rare earth and its energy transferred to another lanthanide, able to emit effectively at close to double frequency [4]. So far, approximately 16 % of the absorbed photon energy in the infrared was actually converted into photons of twice the energy.…”

“…e potential efficiency gain is 3 percentage points per decade. Note that the maximum concentration of solar flow is limited to a factor of 42 600 3 by thermodynamics: the image of an object cannot be hotter than the object itself 4 . One can calculate the maximum value of free energy which can be extracted for each absorbed photon ( fig.…”