FULL-SPECTRUM PHOTOLUMINESCENCE ANALYSIS OF BAND TAILS AND QUASI-FERMI-LEVEL SPLITTING FOR VOLTAGE-LOSS PARTITIONING IN CIGS SOLAR CELLS

Standard Shockley–Queisser (SQ) loss analysis of CIGS solar cells assumes step-like absorptivity, ignoring both band-tail absorption and the quasi-Fermi-level splitting (QFLS). We extract the tail energy γ, QFLS Δµ, and bandgap E_g of CIGS absorbers simultaneously from a single photoluminescence spectrum using a generalized Planck law. For two devices (18.0% and 16.9% efficiency), we obtain γ = 17 and 22 meV and Δµ = 0.76 and 0.69 eV, consistent with EQE analysis. Including these parameters lowers the radiative-limit V_OC by 27 and 49 mV, reassigning part of the apparent nonradiative deficit to the tail-enhanced radiative saturation current. The corrected nonradiative losses (180 vs. 174 mV) now match the nearly identical TRPL lifetimes of the two absorbers (80 vs. 76 ns), resolving an apparent contradiction of the SQ analysis and providing a more realistic partitioning of the V_OC losses.