Impact of bulk properties and local secondary phases on the Cu2(Zn,Sn)Se4 solar cells open-circuit voltage

Abstract

a b s t r a c tAs the development of kesterite solar cells accelerates, the bottlenecks in device performance need to be identified and ways for their circumvention defined and developed. In this work, we use 2-dimensional (2D) numerical simulations to explore possible reasons for low open-circuit voltage (V oc ) in Cu 2 (Zn,Sn) Se 4 (CZTSe) solar cells. High defect density in the CZTSe absorber and at the CZTSe/CdS interface can be significant reasons for V oc deficit, but they do not explain all of the losses observed experimentally. Local deviation from stoichiometry could create secondary phases with a lower band gap compared to the absorber. These secondary phases can be severely harmful to V oc if located in the vicinity of the heterointerface and along the grain boundaries.

Complex Surface Chemistry of Kesterites: Cu/Zn Reordering after Low Temperature Postdeposition Annealing and Its Role in High Performance Devices

“…This could be a further reason for the observed V oc increase because Cu rich grain boundaries can decrease the bandgap of CZTSe locally which is reported to be detrimental to device performance (V oc ) due to enhanced recombination, as theoretical simulations suggest. 44 This is in line with recent nanoscale investigations of grain boundaries in high performance CZTSSe device where Cu poor grain boundaries are observed after air annealing. 9 However, different to the findings of K. Sardashti et al 9 for CZTSSe absorbers no SnO x could be evidenced in the grain boundaries.…”

Simulation of a thin film solar cell based on copper zinc tin sulfo-selenide Cu2ZnSn(S,Se)4

“…All these optimization results give helpful indication for feasible fabrication process. Relative permittivity, ε r 10 13.6 [33] Electron mobility, µ n (cm 2 /V.s) 100 100 [33] Hole mobility, µ p (cm 2 [33] Hole recombination velocity at CdS front surface, S p (cm/s) 10 7 - [35] Electron recombination velocity at CZTSSe back surface, S n (cm/s) -10 7 [35] Defect density, N t (cm -3 ) 1×10 17 1.35×10 15 [34] Electron capture cross section, σ e (cm 2 ) 10 -17 10 -14 [34] Hole capture cross section, σ h (cm 2 ) 10 -13 10 -14 [34] General device properties Reflectivity, R 0.1 [36] Series resistance, R s (Ω-cm 2 ) 0.72 [15] Shunt conductance, G sh (Ω -1 -cm -2 ) = 1/ R sh 1.61×10 -3 [15] Diode ideality factor Q 1.45 [15] Cell temperature, …”

Loss mechanisms influence on Cu2ZnSnS4/CdS-based thin film solar cell performance

“…Table 1 shows ZnO:Al, ZnO and CdS material parameters used in the simulation which were selected based on experimental values reported on literature and theory. These parameters have been broadly used for modeling CIGS, CdTe and kesterite solar cells [23,25,26,[28][29][30][31]. On the other hand, most CZTS material properties used in the simulation were taken from the electrical and optical characterization results reported for CZTS-based solar cells with record efficiencies [1,32].…”