Fabrication and characterization of CuO based heterojunction solar cells

Cupric oxide (CuO) is one of the potential candidates for photovoltaic (PV) industry because of its exceptional electronic and optical properties. Despite attempts by several researchers improve the performance of the CuO-based solar cells, both Voc and Jsc remain low for practical applications. The quality of CuO and the interface quality at the p/n junction are crucial. Lower carrier concentration, higher series resistance of absorber layer and poor carrier collection efficiency are the possible reasons for lower conversion efficiency these solar cells In this thesis, the influence of CuO absorber quality and heterojunction interface properties on the efficiency of CuO based heterojunction solar cell are investigated in detail. Novel layer designs have been used to enhance the carrier collection efficiency of p-CuO/n-Si heterojunction solar cells by studying a series of layer structures prepared by sputtering method. The optical, electrical, microstructural, material quality, chemical composition, surface morphology and photovoltaic properties have been systematically investigated. It is shown that the material quality of the deposited films and interface properties at p-n heterojunction can be significantly improved by tuning the sputtering power and working pressure during the film deposition. A two-step sputter deposition method was adopted to reduce the effect of poor interface quality due to Cu-rich interlayer at the heterojunction. In addition, the effect of Ti doping to improve the conductivity of the CuO films has been studied to obtain lower sheet resistance in CuO films, while retaining the optical properties and crystal quality. Photovoltaic properties with a VOC of 421 mV, JSC of 4.5 mA/cm2 and a photocurrent of 8.3 mA/cm2 have been achieved for p-CuO/n-Si heterojunction solar cells. The efficiency of the device is about 1.21%, which is the highest reported value. Further, a novel method has been demonstrated to obtain significantly higher short-circuit current and fill-factor with front surface field (FSF) design, using Al followed by N doping of the CuO layer. The improvement in Jsc and FF is attributed to the enhancement of charge carrier collection and increase in the carrier concentration. Finally, a new compact model has been proposed for easily predicting the physical parameters of solar cells focusing the improvement of predicted series resistance. It has been shown that the proposed compact model could predict the physical parameters with high accuracy, using several examples.DOCTOR OF PHILOSOPHY (EEE