CaTiO₃:Er³⁺,Ni²⁺broadband‐sensitive upconverter: An effective way to harvest unused NIR solar irradiation for crystalline silicon solar cells

Abstract

We have realized broadband‐sensitive upconversion (UC) in CaTiO3:Er3+,Ni2+ that can harvest 1060–1630 nm photons, which are not utilized by present crystalline silicon (c‐Si) solar cells, and upconvert to 980 nm. The Ni2+ sensitizers absorb 1060–1450 nm photons and efficiently transfer the energies to the Er3+ emitters. In addition to 1450–1630 nm photons that are directly absorbed by the Er3+ ions, 1060–1450 nm photons are also upconverted to 980 nm by the Er3+, Ni2+ codoped upconverter, leading to a more remarkably enhanced conversion efficiency of c‐Si solar cells compared to conventional Er3+‐only doped upconverters. Codoping with Nb5+ to compensate for the charge imbalance caused by the Ni2+ doping at the Ti4+ sites intensified the UC emission. Similarly, charge imbalance caused by the Er3+ doping at the Ca2+ sites was compensated by codoping with alkali ions (Li+, Na+, K+), resulting in a significant improvement in the UC emission intensity. Nearly 6.5‐fold intense UC emission was realized in the newly developed CaTiO3:Er,Ni upconverter compared to the previously reported CaZrO3:Er,Ni one. It is explained on the basis of higher Ni → Er energy transfer efficiency and a more efficient Er3+ UC emission. If these upconverters are applied at the rear‐face of a bifacial c‐Si solar cell, ∼4.8% absolute efficiency improvement is possible.

Effect of Ti compositions for efficiency enhancement of CaTiO3:Er3+,Ni2+ broadband-sensitive upconverters

“…Recently, we have successfully demonstrated a broadbandsensitive UC using Ni 2+ sensitizers and Er 3+ emitters in the ABO 3 type perovskites, such as CaZrO 3 and La(Ga,Sc)O 3 , that can absorb photons at 1100-1600 nm wavelengths range and efficiently upconvert to the c-Si solar cell absorption range. [14][15][16] Moreover, six-coordinated Ni 2+ ions located at the centre of the BO 6 octahedra of the ABO 3 type perovskites harvest photons of 1100-1400 nm wavelength range and transfer the energies to the nearby Er 3+ ions. Consequently, Er 3+ ions upconvert to 980 nm that is within the c-Si absorption range.…”

A broadband‐sensitive upconverter: Garnet‐type Ca3Ga2Ge3O12 codoped with Er3+, Y3+, Li+, Ni2+, and Nb5+

“…Instead, Li + charge compensators of the same amount of the Er 3+ dopants were introduced. Compared with other alkali elements of Na + and K + , Li + introduction improves the UC performance, because of its smaller ionic radius and resultant more notable lattice and crystal field distortion . Furthermore, to enhance the distortion more significantly, Li + was further incorporated with the same amount of Y 3+ that is optically inert and its ionic radius is close to that of Er 3+ .…”

Enhancing IR to NIR upconversion emission in Er3+-sensitized phosphors by adding Yb3+ as a highly efficient NIR-emitting center for photovoltaic applications

“…22 Subsequently, some other host materials such as fluoride glass, NaGdF 4 , Gd 2 O 2 S, and CaTiO 3 were also adopted to explore the application of UCL materials in enhancing the efficiency of silicon-based PV devices. [23][24][25][26] Fischer et al in 2015 reported an external upconversion quantum yield (UCQY) as high as 9.5% for monocrystalline BaY 2 F 8 :Er 3+ upon monochromatic excitation at 1520 nm. This value is similar to its internal UCQY (10.1%) and higher increases in the short-circuit current density are achieved compared with using microcrystalline β-NaYF 4 :Er 3+ , which can be well understood that transparent materials show stronger absorption and less scattering in comparison to opaque phosphors.…”