Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 12: Photovoltaics (Joint session of HL and DF, organized by HL)

HL 12.10: Vortrag

Montag, 7. März 2016, 17:45–18:00, H2

Investigation of shallow defects in Cu(In,Ga)Se₂ with time-resolved photoluminescence — •Torsten Hölscher, Matthias Maiberg, Setareh Zahedi-Azad, and Roland Scheer — Martin-Luther-Universität Halle-Wittenberg, 06120 Halle(Saale), Germany

Time-resolved photoluminescence (TRPL) is a powerful method to observe the recombination kinetics of minority carriers in solar cell materials like Cu(In,Ga)Se₂ (CIGSe). The influence of a shallow defect (traps) close to the conduction band leads to bi-exponential and curved TRPL-transients due to trapping of minority carriers. TRPL-measurements under increased device temperatures revealed a strong reduction of the second longer decay time, which is may be attributed to the temperature enhanced restitution of the trapped carriers to the conduction band. Saturation of shallow and deep defects became observable by varying the excitation of excess carriers. With Synopsys TCAD^Ⓡ we simulated the recombination behavior of minority carriers in CIGSe as a function of temperature and excitation in the presence of shallow defects. In comparison with the experiments, we obtained in the simulations E_C−E_t≈200 meV for the energy level, σ_n≈10⁻¹³ cm² for the electron capture cross-section and N_t≈10¹⁶ cm⁻³ for the density as significant parameters of the trap-state. These trap parameters closely match the N1 admittance signature detected previously - a signature which explanation has been heavily disputed. Our findings now support the explanation of the N1 defect as due to a minority carrier trap. We will discuss the influence of this trap on the solar cell performance.