Minority-carrier lifetime and efficiency of Cu(In,Ga)Se2 solar cells

Abstract

Room-temperature recombination dynamics has been investigated in a large set of different Cu(In,Ga)Se2 absorber films and compared to the electrical device characteristics of the respective solar cell modules. For a given cell preparation process, a characteristic relation between the low-injection minority-carrier lifetime of the absorber layers and the conversion efficiency of the solar cells is observed: Long lifetimes correlate with high open circuit voltages and conversion efficiencies, while no significant influence of the lifetime on the short circuit current is found.

Cu2ZnSnSe4 Thin‐Film Solar Cells by Thermal Co‐evaporation with 11.6% Efficiency and Improved Minority Carrier Diffusion Length

“…The minority carrier lifetime ( τ ) is estimated by fi tting the decay of PL signal to a rate equation that takes into account linear and quadratic recombination processes. [ 27 ] We measure τ of roughly 2-2.5 ns for both of the sulfi de and selenide devices at roomtemperature. With the estimated L D of ≈2.1 µm and the relation of / D e L k T q τμ = where k is the Boltzmann constant and T is the temperature, we can then estimate the electron mobility ( µ e ) of our CZTSe fi lm to be ≈690 cm 2 V −1 s −1 , over a factor of two higher than that measured in CZTSSe devices.…”

Beyond 11% Efficiency: Characteristics of State‐of‐the‐Art Cu2ZnSn(S,Se)4 Solar Cells

“…This value is less than the band gap of the absorber layer ( E g = 1.13 eV) as determined from the QE data. Although this may suggest a dominant band to impurity (or band tail) radiative recombination channel contributing to the PL emission, it is also possible that this difference may result from inhomogeneity in the absorber, with the PL spectrum being dominated by the region luminescing at the lowest energy, [ 25 ] whereas the QE is a more spatially averaged quantity. In order to observe such a shift in the PL spectrum with respect to the average band gap, the diffusion length should exceed the length scale of the fl uctuations.…”

“…The decay curves, which do not follow a simple mono-exponential decay, can be modeled by the rate equation that takes into account both linear and quadratic recombination processes. [ 25 ] However, even when the quadratic recombination processes are taken into account, the TRPL data cannot be adequately fi tted with a single lifetime and lifetimes ranging from 5-8 ns for the 1.13 eV devices (9-14 ns for the 1.09 eV C6 device) are obtained as the time scale increases. The observed bending in the TRPL spectrum may be understood once the prospective spatial inhomogeneity of the samples is taken into account (i.e., see discussion above regarding the QE data), with the measured TRPL signal having individual contributions from different regions with varying lifetimes.…”

Prospects and performance limitations for Cu–Zn–Sn–S–Se photovoltaic technology

“…We performed TR-PL measurements on the 10.1 per cent CZTSSe and the 15.2 per cent CIGSSe completed devices using a 532 nm laser excitation [125], as shown in figure 8. The minority carrier lifetime is extracted from a quadratic rate model as described in Ohnesorge et al [126]. A lower CZTSSe device minority carrier lifetime (3.1 ns) is obtained compared with the higher performance CIGSSe cell (5.4 ns).…”