Abstract:
This study focuses on the utilization of earth abundant materials for absorber layer of photovoltaic device, Cu based I2-II-IV-VI4 quaternary kesterite Cu2ZnSn(SxSe1-x)4 (CZTSSe) can be regarded as potential candidate. The constituent elements of this photo-absorber material are earth abundant and possess no severe threats in the environment sector. The theoretical Schockley-Queisser efficiency of CZTSSe is ~32% under AM 1.5. But unfortunately, the maximum possible efficiency achieved is 12.6% having Voc = 513.4mV, Jsc = 35.2 mA/cm2 and fill factor = 69.8%. The chief reason for the lower e ciency is its lower Voc. So, in this study the current champion cell termed as device A is taken as the standard and numerical modeling is done. In order to achieve higher efficiency an improved structure termed as device B has been proposed and compared with the current champion cell. The improved structure has a type II staggered type band structure unlike the type I straddling type band structure seen in device A. This resulted high Voc but low Jsc. But the overall performance gain was the increase in efficiency. For indoor lighting condition the theoretical Schockley-Queisser efficiency limit is ~60%. Under indoor lighting condition the device A achieved an efficiency of 13.77% whereas device achieved an efficiency of 15.85%. The increase in the efficiency is attributed to higher photon yield for indoor lighting. As part of the study both the modeled device was connected with a power electronic converter to drive a small sensor node operating with a bias voltage of 5V. The converter used is a self-oscillating dc-dc converter based on the concept of boost converter. Since it is self-oscillating it does not require additional circuitry for driving the switch used in the converter and operates in discontinuous conduction mode (DCM). Device A performed better than device B with the self oscillating converter. On the other hand device B had better performance with a conventional boost converter in continuous conduction mode (CCM).
