Simulation of heat loss in Cu₂ZnSn₄S_xSe_4−x thin film solar cells: A coupled optical-electrical-thermal modeling

A coupled optical-electrical-thermal modeling has been developed to investigate the heat generation and dissipation in Cu₂ZnSn₄S_xSe_4−x thin film solar cells. Five heat generation factors: Thermalization, Joule heat, Peltier heat, Surface Recombination heat, and non-radiative recombination heat (Shockley-Read-Hall and Auger) as well as two heat dissipation factors convective and radiative cooling were calculated and displayed in 2 and 3 dimensional maps. Thermalization is the dominant heat generation factor in the cell independent of the voltage. The non-radiative recombination heat and Joule heat depend on voltage. Apart from these bulk heating factors, the surface recombination heat and Peltier heat were also investigated. The surface recombination heat is higher at open-circuited voltage (V=V_oc) compared to at V = 0 while the Peltier heat is zero at V=V_oc which can be explained by looking at the energy band diagrams at these voltages. The total heat generation has a small gradient across the cell thickness (<5 × 10⁹ W/m³) as the cell is quite thin. However the V_oc decreases from 0.54 V to 0.49 V (ΔV = 0.047 V). The temperature shows small gradient across the cell (0.01 K). However, the initial temperature (293 K) increases to 315–320 K during the operation as studied by the coupled study. A higher temperature did not change the J_sc but the fill factor decreases from 73.8% to 71.8% and the PCE falls by 11.11% (from initial 12.78%–11.36%). All the total heat dissipation, convective, and radiation cooling follow a similar trend to the total heat generation but convective cooling is the dominant component of dissipation. We compared our simulation results with literature data for heat impact on device characteristics of kesterite thin film solar cells.