¢ó - ¢õ Compound Semiconductor Solar Cell Interface Features

III-V compound semiconductor multijunction tandem solar cells have very high efficiency with sub-cells absorbing each part of the solar spectrum. The existing triple junction devices have achieved efficiencies over 42%, and further efficiency increases depending on optimizing structure and controlling hetero-interface characteristic.So, in this thesis, theoretical and experimental investigations of triple-junction solar cells have been carried out about the interface aspects. The following outstanding results have been obtained:(1) The theoretical study for energy losses, recombination mechanisms and transport processes in solar cells has been conducted, and the resolvent for reducing energy loss and recombination were also discussed.(2) The structure design model of multijunction solar cell has been obtained, in which a programme has been made to valuate the quantum efficiency, reflectance spectrum, current voltage characteristic of the device.(3) The rectifying characteristic of heterojunction in top cells and middle cells has been investigated, and one important finding was the rectifying characteristic of the n++-GaInP2/N+-AlInP2 heterojunction between middle cell and tunnel junction, which can result for the failure of tandem cell under low temperature (about-80 Celsius). By increasing the doping concentration of N+-AlInP2window layer of the middle cell or replacing it with n-GaInP2, the rectifying characteristic can be eliminated.(4) As another notable achievement, interference phenomena of herointerface in the triple junction solar cell was investigated in detail. By optimizing ARC, the window layer and back suiface field of the top cell, tunnel junction, the window layer of the middle cell, interference phenomena has been successfully minimized.(5) From above investigations and the improvement of device process, the GaInP2GaAs/Ge triple junction solar cells have achieved efficiencies 29.1% under AMO spectrum and over 37% under AM1.5D Low AOD(312X), and the GaInP2/GaAs/InGaAs triple junction solar cells have achieved efficiencies 27.4%(AM0).Among these results, there are two remarkable achievement, the first is the finding of a failure mechanism in the triple junction solar cell under low temperature conditions, which is extremely important for space applications. The second achievement is the the deep investivation of interference phenomena of herointerface in the triple junction solar cell. The interference phenomena can reduce photon absorption, and result for mismatched current between top cell and middle cell. By optimizing structure design, this loss can be minimized.Finally, further work plan has been submitted as following:(1) Develop a broadband anti-reflective coatings and improve front fingers;(2) Develop a comprehensive understanding of degradation mechanisms and their root causes;(3) Develop predictive understanding of lattice mismatched epitaxy;(4) Develop a deeper understanding of interface and bulk traps, recombination mechanisms, transport processes;(5) Develop a deeper understanding of band gap narrowing, non-local impact ionization, lattice heating, photon recycle.