Sentaurus modelling of 6.9% Cu2ZnSnS4 device based on comprehensive electrical & optical characterization

Abstract

In this work we perform comprehensive characterization on a 6.9% pure sulphide Cu 2 ZnSnS 4 (CZTS) device and construct a 2D device model in Sentaurus TCAD to identify possible roots of performance bottlenecks. Electrical and optical parameters of the absorber from comprehensive electrical and optical characterization, together with other necessary parameters from literature, we successfully reproduce measured current density-voltage (J-V) and external quantum efficiency (EQE) curves. Absorption coefficient is extracted by fitting measured internal quantum efficiency (IQE). At the buffer/absorber interface, a surface recombination velocity of 1×10 5 cm/s is identified to adequately describe measured spectral response at the near-interface region. Furthermore, a bulk lifetime of ~29 ns is extracted from effective lifetime modelling in conjunction with time resolved photoluminescence (TRPL) results. The key underlying V oc deficit, ~200 mV, is pinpointed to bandgap fluctuation, which is backed by the simulation study on both QE tail and steady state photoluminescence.

Spectral Responses in Quantum Efficiency of Emerging Kesterite Thin-Film Solar Cells

“…To be consistent with the reported literature, theories, or reasonable estimates, capture cross sections are fixed at 1.0 · 10 À12 cm 2 for electrons and 1.0 · 10 À15 cm 2 for holes at donor-type defect and at 1.0 · 10 À15 cm 2 for electrons and 1.0 · 10 À12 cm 2 for acceptor-type defect [12,[28][29][30][31][33][34][35][36][37]. For a comparative study of the ideal device in the previous section, the device structure is updated with very thin (5 nm) defective interface layer between CdS and CZTSSe.…”

“…The absorption coefficient, α(λ) was taken from Ref. [28] and the front surface recombination velocity (S f ), the default depletion width is 0.3 µm, and the electron lifetime (τ n )w e re1 0 3 cm/s and 10 À9 s [29,30]. In Figure 3, the Q-E shape changes disproportionally with significant red light response reduction >600 nm as the uncompensated impurity concentration changes , and 10 À11 s.…”

Status of materials and device modelling for kesterite solar cells

“…Although modelling and characterisation by isolating each of the three categories' properties is not trivial, numerical simulators such as TCAD [32], SCAPS [34], and PC1D [35] can provide further insight with the support of empirical results. To optimise modelling and simulation results, the main characterisation methods are time-resolved photoluminescence, photoluminescence, quantum efficiency, admittance spectroscopy (AS), deep-level transient spectroscopy, capacitance-voltage, and current-voltage methods, while varying temperature, frequency, light intensity, and light/voltage biases.…”

“…From the single crystalline absorber study without grain boundary effects, interface recombination and the bulk minority carrier lifetime of the absorber are required to be improved. The bulk minority carrier lifetime is estimated to be between 2 and 7 ns with minority diffusion length 2.1 μm [32]. To improve the minority carrier lifetime and reduce bulk recombination, passivating bulk defects and associated interface defects is required.…”

“…The 12.6% champion device has demonstrated a triangular shape of quantum efficiency, implying a strong carrier collection loss at the heterojunction interface. In a simulation study, the interface recombination velocity is estimated to be approximately 10 5 cm s −1 , based on quantum efficiency measurements [32]. Hence, extensive modelling of the heterojunction interface has been focussed on optimising the interface band offset, improving defective CdS buffer layers, and investigating alternative buffer/window layers.…”