Self-absorption in upconverter luminescent layers: impact on quantum yield measurements and on designing optimized photovoltaic devices

Abstract

This Letter details a theoretical investigation of self-absorption within an upconverter (UC) material, consisting of trivalent erbium (Er3+)-doped hexagonal sodium yttrium fluoride (β-NaYF4) and its implications on two experimental situations: the case of a quantum yield measurement, and on the effective performance in a UC-enhanced photovoltaic (PV) device. The study demonstrates that an optimization of the thickness is essential in order to reduce the effect of self-absorption and maximize the possible additional photocurrent that could be harvested. It also has been found that the external photoluminescence quantum yield (ePLQY) measured through an integrating sphere may result in an underestimation with respect to the performance that the UC material could achieve in a UC-PV device. Finally, it has been found the optimal thickness and the molar concentration of Er3+ ions are inversely proportional, suggesting that an optimal number (1.3-2.9·10(17)) of Er3+ ions should be contained within the UC layer.

Upconversion for Photovoltaics – a Review of Materials, Devices and Concepts for Performance Enhancement

“…In the upconverting solar cell device, a mirror reflects the excitation light, which results in an effective higher irradiance and thus lower optimum thicknesses are found in comparison to the simulated measurements using an integrating sphere. The decreasing optimum thickness at simultaneously higher optimum concentration levels results in the situation that, for the investigated irradiance regime from 0.1 to 10 W cm −2 , there is an optimum area density of Er 3+ ions of 2.8 × 10 20 cm −2 . At higher irradiance values, this number of ions is distributed over a thicker sample; at lower irradiance a thinner sample is more beneficial.…”

“…Increasing the dopant concentration not only increases the absorption of incident photons, but also the self‐absorption of emitted photons. Taking into account this self‐absorption, Boccolini et al performed a theoretical analysis in which they investigated the external UCQY of Er 3+ ‐doped β ‐NaYF 4 . They simulated two situations: the measurement of the external UCQY with an integrating sphere setup, and the electrical characterization of an upconverter solar cell device with a mirror at the rear side.…”

Upconversion solar cell measurements under real sunlight

“…UCQY values above 10% have been reported for different microcrystalline and single crystal material system when using laser illumination with irradiances below 1 W/cm 2 . 11,[16][17][18][19][20] The upconversion process in Er 3+ is well described in literature [21][22][23] and the corresponding basic energy level diagram is shown in Figure 2a. In short, after ground state absorption (GSA) of photons with wavelengths of around 1500 nm ( 4 I15/2→ 4 I13/2) the excitation energy may hop around in the crystal via energy transfer from Er 3+ ion to Er 3+ ion.…”

Development of ytterbium-doped oxyfluoride glasses for laser cooling applications

“…al. have reported on the pump power dependence studies of upconversion (UC, process consisting in the absorption of two or more photons of low energy followed by the emission of one photon of higher energy) PLQY in Er 3+ : β -NaYF 4 nanocrystals by considering the effect of reabsorption for solar cell applications42. This is the first time to the best of our knowledge that the pump power dependence PLQY of Yb 3+ -doped glasses for laser cooling prospective is reported by considering.…”