Spatially resolved measurements of charge carrier lifetimes in CdTe solar cells

Abstract

The lifetime of the minority charge carriers in polycrystalline Cadmium Telluride (pc-CdTe) for solar cell applications is a crucial material parameter and has been determined by analysis of the decay curves of the luminescence signal. Both the lateral and the transversal distributions of the carrier lifetime on the surface and in the bulk of pc-CdTe material as well as the respective solar cell characteristics were measured as a function of the deposition technique, the activation treatment, and the incorporation of additional group-V elements. The results are compared to prior studies. It was found that an activation process passivates grain boundaries and increases the carrier lifetime, which is then higher at the pn-junction than at the surface. Furthermore, nitrogen and phosphorus doping of the CdTe absorber material influences the charge carrier lifetime. The results show that the spatial resolved measurement of the carrier lifetime in pc-CdTe gives an important insight to the charge carrier dynamics of the material.

Grain boundaries in CdTe thin film solar cells: a review

“…Luminescence techniques do though allow far greater extraction of additional spectroscopic information about GBs than either EBIC or scanning probe methods. Additional analysis has shown that carrier lifetime is reduced at the boundary [139] whilst recombination velocity is significantly increased [140], which Kanevce et al [141] link to V OC loss. Comparison with electron back scattered (EBSD) analysis also shows Σ3 twins are typically inert with little enhancement in recombination [142,144], presumably due to a lack of dangling bounds as posited by Consonni et al [148].…”

“…Surveying the CdTe grain boundary luminescence literature as a whole, two key points become apparent. Firstly, these techniques show an increase in non-radiative recombination at the GBs compared to GIs [60,[137][138][139][140][141][142][143][144][145][146] and secondly this recombination at GBs is significantly reduced following CdCl 2 treatment [138,139,143,144]. This is typically manifest through a reduction in observed exciton related luminescence at the GBs compared to GIs (see figure 10), with that reduction being minimised following CdCl 2 treatment.…”

Charge Carrier Lifetime Fluctuations and Performance Evaluation of Cu(In,Ga)Se2 Absorbers via Time‐Resolved‐Photoluminescence Microscopy

“…Other systems, more accessible, implement one‐photon excitation. [ 17 ] However, for diffraction‐limited beam sizes (i.e., confocal mode), it is extremely challenging to achieve high optical resolution and remain in low injection for CIGS. A different—and complementary—approach is the use of wide‐field (or uniform) illumination.…”

Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure

“…Manufacturing efficient cadmium telluride (CdTe) solar cells with >21% power conversion efficiency requires postdeposition treatment with cadmium chloride (CdCl 2 ) . This treatment results in recrystallization of the CdTe layer, producing larger, more uniform grains. − However, efficiency improvements cannot be attributed solely to microstructural changes because single-crystal CdTe exhibits poor photovoltaic performance − and CdTe films deposited at high temperature show increased efficiency with CdCl 2 treatment despite minimal changes in grain size. , …”