Combined electrical and optical characterisation of recombination mechanisms and minority carrier lifetime in solar cells

This work presents the development of a measurement system which combines optical and electrical characterisation of carrier lifetime and recombination mechanisms of thin film solar cells. It combines spectrally-resolved photoluminescence (PL), time-resolved photoluminescence (TRPL), and transient photocurrent (TPCD), which are measured using a single excitation laser source at the same spot of the solar cell. Initial PL, TRPL and TPCD measurements have been conducted on CdS/CdTe and MZO/CdTe samples. The resulting PL spectra show emission peaks corresponding to the material bandgap. Under the same excitation conditions and same measurement spot, initial TRPL and TPCD measurements were successfully conducted, yielding effective carrier lifetime values (τ1=1.39ns, τ2=3.91ns) and (τ=40.5ns), respectively for the CdS/CdTe sample and (τ1=0.98ns, τ2=3.3ns) and (τ=36.8ns), respectively for the MZO/CdTe sample. These values are affected by different recombination processes in solar cells. Therefore, as well as characterising solar cell material quality, the electronic properties of the finished PV device can also be characterised.