Organic/inorganic hybrid solar cells based on electroplated CdTe.

The purpose of this work is to develop organic/inorganic hybrid solar cells based on electroplated CdTe. The materials used in this research are CdS, CdTe and PAni. These materials have been characterised by XRD, Raman spectroscopy, EDX, SEM, AFM, UV-Vis spectroscopy, PEC, C-V and DC measurements, UPS and PL for their structural, compositional, morphological, optical, electrical and defect properties. CdS has electrodeposited from the electrolyte using (NH[4])[2]S[2]O[3] as the sulphur source. The optimum growth voltage (V[g]) and temperature (T[g]) are obtained at 1455 mV and 85°C, respectively. The best annealing condition is found to be at 400°C for 20 minutes in the presence of CdCl[2]+CdF[2]. CdTe thin films were electrodeposited from CdCl[2] precursor and a comprehensive study was carried out for the first time. The work has demonstrated a better understanding of material issues and some clues on the effect of CdCl[2] treatment. The optimum V[g] and annealing condition were obtained at 698 mV with respect to the calomel electrode and 420°C for 20 minutes in the presence of CdCl[2]+CdF[2] or CdCl[2]+CdF[2]+GaCl[3]. The development of PAni thin films has been established using anodic and cathodic deposition. The pernigraniline salt PAni grown from anodic has an amorphous structure, large bandgap and cementing growth effect while leucoemeraldine salt PAni grown from cathodic deposition shows the best crystallinity at V[g]=1654 mV with respect to carbon anode, smaller grain size, higher resistivity and lower bandgap. The CdS, CdTe and PAni thin films have been studied in device structures, assessing their solar cell device performance. The best of CdS/CdTe solar cell was observed with efficiency of 5.8% when using CdS thin film treated with CdCl[2]+CdF[2] at 400°C. The best solar cell from CdTe study shows the efficiency of 6.8% when using CdTe thin films treated with CdCl[2]+CdF[2] at 420°C. Further study demonstrates that a device with g/FTO/n-CdS(~200 nm)/n-CdTe(~1200 nm)/p-CdTe(~300 nm)/Au shows high J[sc] and highest efficiency (7.7%) due to the formation of n-n heterojunction, p-n homojuction and ohmic contact within the structure. The efficiency of the solar cell increased from -2.4% to -4.2% when incorporating -81 nm thick PAni layer grown from anodic deposition. The devices incorporating ZnS, ZnTe and CdSe layers show the prospect of graded bandgap solar cell, but proper optimisation on each material should be carried out before using in multi-layer device structures. The study on the lifetime of solar cells show slow degradation and it maintained more than 83% of its initial efficiency after 9,000 hours.