Abstract
AbstractWe study the impact of different alkali post‐deposition treatments by thermal admittance spectroscopy and temperature‐dependent current‐voltage (IVT) characteristics of high‐efficiency Cu(In,Ga)Se2 thin‐film solar cells fabricated from low‐temperature and high‐temperature co‐evaporated absorbers. Capacitance steps observed by admittance spectroscopy for all samples agree with the widely observed N1 signature and show a clear correlation to a transport barrier evident from IVT characteristics measured in the dark, indicating that defects are likely not responsible for these capacitance steps. Activation energies extracted from capacitance spectra and IVT characteristics vary considerably between different samples but show no concise correlation to the alkali species used in the post‐deposition treatments. Numerical device simulations show that the transport barrier in our devices might be related to conduction band offsets in the absorber/buffer/window stack.
Highlights
The beneficial effect of sodium (Na) on the efficiency of Cu(Ga,In)Se2 (CIGS) thin‐film solar cells was discovered more than 2 decades ago.[1]
We study the impact of different alkali post‐deposition treatments by thermal admittance spectroscopy and temperature‐dependent current‐voltage (IVT) characteristics of high‐efficiency Cu(In,Ga)Se2 thin‐film solar cells fabricated from low‐temperature and high‐temperature co‐evaporated absorbers
Post‐deposition treatments (PDT) of the as‐grown absorber consist of depositing thin layers of alkali fluorides and have proven to be a successful route to supply additional alkali species beyond Na diffusing from the soda‐lime float glass (SLG) substrate.[2]
Summary
The beneficial effect of sodium (Na) on the efficiency of Cu(Ga,In)Se2 (CIGS) thin‐film solar cells was discovered more than 2 decades ago.[1]. Despite the good agreement between all 3 activation energies for many samples, we observe deviations for 2 types of samples: FIGURE 6 Correlation between the activation energies determined from IVT measurements (squares: effective series resistance Rs, circles: dark current density Jd) and from the admittance spectrum.
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