An efficient light converter YAB:Cr3+,Yb3+/Nd3+ with broadband excitation and strong NIR emission for harvesting c-Si-based solar cells

Highly efficient Cr3+- and Yb3+/Nd3+-co-activated YAl3(BO3)(4) (YAB) phosphors have been developed as spectral convertors for improving silicon solar cell photovoltaic conversion efficiency. In the YAB lattice, Cr3+ ions act as broadband spectral sensitizers by absorbing UV-Vis (370-750 nm) photons, which are not absorbed by the silicon solar cell. After energy transfer, the Yb3+ acceptors then exhibit strong NIR emission centered at around 1000 nm, which is coupled well with the absorption band of the silicon solar cell. Efficient energy transfer is reflected by a sharp decrease in the excited state lifetime and red photoluminescence (PL) from Cr3+ with increasing Yb3+ concentration. Further evidence in favor of energy transfer is that PL-excitation spectra of NIR luminescence from Yb3+ are identical to those of deep red emission from Cr3+. Trivalent ions Gd3+, Bi3+ and La3+ have been introduced into YAl3(BO3)(4):Cr3+, Yb3+ in this study for a stronger NIR PL intensity. Additionally, energy transfer from Cr3+ to Nd3+ is also observed. Yb3+, Nd3+-co-activated YAB shows much broader NIR emission. Due to the effective absorption of Cr3+ in the visible region in YAB and the efficient energy transfer to Yb3+/Nd3+, these materials can be developed as spectral convertors to improve silicon solar cell photovoltaic conversion efficiency.