Luminescence of Cu2ZnSnS4 polycrystals described by the fluctuating potential model

Abstract

The growth of Cu2ZnSnS4 (CZTS) polycrystals from solid state reaction over a range of compositions, including the regions which produce the highest efficiency photovoltaic devices, is reported. X-ray measurements confirm the growth of crystalline CZTS. Temperature and intensity dependent photoluminescence (PL) measurements show an increase in the energy of the main CZTS luminescence peak with both increasing laser power and increasing temperature. Analysis of the PL peak positions and intensity behavior demonstrates that the results are consistent with the model of fluctuating potentials. This confirms that the polycrystals are heavily doped with the presence of a large concentration of intrinsic defects. The behavior of the main luminescence feature is shown to be qualitatively similar over a broad range of compositions although the nature and amount of secondary phases vary significantly. The implications for thin-film photovoltaic devices are discussed.

Nanometre-scale optical property fluctuations in Cu2ZnSnS4 revealed by low temperature cathodoluminescence

“…6c and reveals a broad featureless peak centred at~917 nm (1.35 eV), similar to previous photoluminescence measurements (e.g. [8,9]). The broadness of the luminescence peak, even at 10 K temperature, makes it difficult to analyse any variations in the spectra between different sample regions using the traditional method of Gaussian curve fitting.…”

“…In this paper we present evidence for spatially non-uniform optical properties in CZTS using cathodoluminescence (CL) in a scanning electron microscope (SEM). Photoluminescence spectra measured from bulk CZTS typically show a broad featureless peak [9], which makes it difficult to extract the underlying recombination pathways. The high spatial resolution in an SEM however provides more local information and by cooling the specimen close to liquid-He temperature the effect of phonon broadening of the luminescence peaks can also be reduced.…”

“…A key difference between CZTS and CIGS is the extensive band tailing in the former [3,5]. Band tailing in CZTS is related to: (i) Urbach tails in absorption and quantum efficiency spectra [5], (ii) broadening of Raman vibration modes [6,7], (iii) S-shaped temperature dependence of the photoluminescence peak [8,9] and (iv) an anomalously long carrier lifetime at low temperature [3,10]. Band tailing is common in highly doped, highly compensated semiconductors and is due to statistical fluctuations in the local dopant (i.e.…”

Physical and electrical characterization of high-performance Cu 2 ZnSnSe 4 based thin film solar cells

“…Despite, the above characterization showing that the formed layer was likely a single CZTSe phase, the PL signal was broad at room temperature. The presence of defects or/and potential fluctuations [10] in the CZTSe structure could explain the broad PL peak since a contribution of sub-band gap recombination remains all the way up to room temperature. The fluctuating potentials could arise either from strong compensation in the material or from stoichiometry variations leading to band gap variation inclusions in the main kesterite absorber material.…”

Radiative transitions in highly doped and compensated chalcopyrites and kesterites: The case ofCu2ZnSnS4

“…Moreover, in the case of polycrystalline semiconductors, local disorder at grain boundaries causes a significant density of electronic states (tails states) within the band-gap energy [20,40,41]. Several PL studies performed on CZTS have shown that at low temperature the spectra are dominated by a broad and asymmetric band centered at around 1.2-1.3 eV as reported for single crystals [24,27,42,43], polycrystals [28,44,45], thin films [31,34,[46][47][48][49], monograin powders [50,51], and nanocrystals [52]. No agreement exists concerning the nature of involved states and also on the nature of the radiative transitions.…”