Characterization of CdS/CdTe thinhyphen;film solar cells by admittance spectroscopy and deephyphen;level transient spectroscopy

摘要

Admittance spectroscopy, deephyphen;level transient spectroscopy, and deephyphen;level optical spectroscopy were used to characterize CdS/CdTe thinhyphen;film solar cells prepared by closehyphen;spaced sublimation. These devices aren+/phyphen;type heterohyphen; (or shallow homohyphen;) junctions, and deep levels in thephyphen;CdTe layer are observed. The energy levels within the band gap can be divided into three groups. The first group consists of the shallow (0.1 eV from the band edge) acceptors and donors, observed in electrical characterization only as the net carrier concentration. A band of midgap levels with activation energies of 0.6ndash;0.8 eV in deephyphen;level transient spectroscopy is observed. The emission rates and activation energies for these levels agree with deep donor levels found innhyphen;type CdTe. A third band of levels is found with activation energies of 0.28ndash;0.45 eV in admittance spectroscopy. These levels are seen in deephyphen;level optical spectroscopy and also in deephyphen;level transient spectroscopy, provided that a large forwardhyphen;bias pulse is used to fill the level. The emission rates in the third band agree with donor levels observed innhyphen;CdTe. Estimates of concentrations suggest that the concentration of the group two defects (midgap donors) is sim;0.8 of the net shallow acceptor concentration.