Widegap CdSe Solar Cells with VOC >750mV

With growing demand for solar energy and as single junction photovoltaic devices approach the SQ limit it is becoming increasingly important for the solar industry to enable multijunction tandems for terrestrial application. While there are numerous promising candidate technologies that can serve as the bottom cell with a bandgap of 1.1 eV, there are no at-scale options that can satisfactorily serve as the top-cell with a bandgap 1.7 eV. Cadmium Selenide (CdSe), with a direct bandgap of 1.72 eV, is a strong candidate material for top-cells in a tandem solar panel. We evaluate the applicability of CdSe thin-film on TCO coated glass as a photovoltaic absorber and find that it is inherently n-doped and wurtzite. The device architecture comprises a CdSe layer deposited onto SnO2:F that was annealed similar to CdTe for improving lifetime, followed by a hole contact material made with PTAA that works as a hole selective layer and a MoO3/Au bilayer that functions as a transparent, high work function contact layer. A bandgap of 1.72 eV was confirmed using PL and UV-Vis data, with Hall and C-V measurements revealing majority carrier concentrations of 10
¹⁶
cm
⁻³
and time resolved photoluminescence suggesting lifetimes close to 5ns. Based on the combination of V
OC,Ideal
extracted from sub-gap EQE and external radiative efficiency measurements, we estimate the absorber to be capable of achieving 1.2V V
OC.
This suggests significant room for research in developing effective hole-selective contact for CdSe.