Er³⁺/Yb³⁺ upconverters for InGaP solar cells under concentrated broadband illumination

Abstract

aThe inability of solar cell materials to convert all incident photon energy into electrical current, provides a fundamental limit to the solar cell efficiency; the so called Shockley-Queisser (SQ) limit. A process termed upconversion provides a pathway to convert otherwise unabsorbed low energy photons passing through the solar cell into higher energy photons, which subsequently can be redirected back to the solar cell. The combination of a semi-transparent InGaP solar cell with lanthanide upconverters, consisting of ytterbium and erbium ions doped in three different host materials (Gd 2 O 2 S, Y 2 O 3 and NaYF 4 ) is investigated.Using sub-band gap light of wavelength range 890 nm to 1045 nm with a total accumulated power density of 2.7 kW m À2 , a distinct photocurrent was measured in the solar cell when the upconverters were applied whereas a zero current was measured without upconverter. Furthermore, a time delay between excitation and emission was observed for all upconverter systems which can be explained by energy transfer upconversion. Also, a quadratic dependence on the illumination intensity was observed for the NaYF 4 and Y 2 O 3 host material upconverters. The Gd 2 O 2 S host material upconverter deviated from the quadratic illumination intensity dependence towards linear behaviour, which can be attributed to saturation effects occurring at higher illumination power densities.

Upconversion thermal enhancement of 2H11/2→4I15/2 of Er3+ and blue emission of impurity Tm3+ in Sr3(PO4)2:Er3+/Yb3+

“…The phonon vibrotational energy of (PO 4 ) structure unit is about 940∼1056 cm −1 , 31 which helps 4 S 3/2 upward transiter to 2 H 11/2 (about 800 cm −1 ) 32 at high temperature to achieve UCL thermal enhancement of 2 H 11/2 → 4 I 15/2 of Er 3+ . Some reports confirmed that the thermal lattice distortions of PO 4 unit with a rotation of the tetrahedra often produce, 33,34 which helps to increasing the 4f→4f transition probability of Er 3+ at high temperature 35 …”

Upconversion luminescence color modulation and temperature sensing of Na0.5Bi2.5Nb2−xTaxO9:Er3+/Yb3+ phosphors

“…15,16 Additionally, the low symmetry of luminescence center can break the parity forbidden of 4f → 4f transitions from symmetrical orbitals, which can enhance UL intensity. 17 Meanwhile, some researchers found high temperature sensitivity in niobate and tantalate. 15,16,18,19 Therefore, Na 0.5 Bi 2.5 Nb 2−x Ta x O 9 (NBN 2−x T x ) with low phonon energy and symmetry was selected as the study F I G U R E 3 Commission International de L'Eclairage (CIE) chromatic diagram of NBN 2−x T x :0.14Er 3+ /0.26Yb 3+ (x = 0, 0.5, 1.0, 1.5, and 2.0) phosphors under 980-nm laser excitation with 29.06 W/cm 2 .…”

“…Compared with other oxide hosts, niobate and tantalate with excellent UL intensities have been studied because low phonon energy hinders the multi‐phonon relaxation 15,16 . Additionally, the low symmetry of luminescence center can break the parity forbidden of 4f → 4f transitions from symmetrical orbitals, which can enhance UL intensity 17 . Meanwhile, some researchers found high temperature sensitivity in niobate and tantalate 15,16,18,19 .…”

Up-conversion mechanisms in Er3+-doped fluoroindate glasses under 1550 nm excitation for enhancing photocurrent of crystalline silicon solar cell

“…Most of these layers comprises near infrared absorption and provide visible and near infrared emissions by the addition of certain types of trivalent lanthanides ions (Ln 3+ ) [6,7]. Among the Ln 3+ , Er 3+ has become one of the most deployed candidate for SC applications due to its energy levels that are multiples of the transition 4 I 15/2 → 4 I 13/2 , which may be activated when excited at wavelengths from 1400 to 1580 nm [8,9].…”