Ivanov I. Photoelectric processes in nanodispersed Si and TiO2 based heterostructures.

Thesis for the scientific degree of the candidate of the physical and mathematical science on speciality 01.04.10 - physics of semiconductors and dielectrics. - Kyiv National Taras Shevchenko University, Kyiv, 2010. This thesis is devoted to investigation of effect of parameters of rear reflectors formed on the basis of SiOx/SiNx layers or porous silicon (PS) layers on the efficiency of bulk multicrystalline silicon solar cells (SC) with textured substrate; determination of the current flow mechanism in dispersed nano-TiO2 photosensitive structures. Square p-type multicrystalline silicon wafer was used as base for SC with dielectric Bragg mirror (BM) manufacturing. BM was formed on rear side of Si wafers at successive deposition of SiОх and SiNx layers by PECVD method. Presence of BM provides the passivation effect on life time of minority charge carriers. For SC with BM the current Isc is higher on 2.1 % and efficiency is higher on 0.17% comparatively with reference SC without BM. BM were also fabricated by electrochemical etching of p-type <100> oriented mono-Si wafers and multi-Si wafers. BM composed of 10 PS bi-layers on the base of p-type <100> oriented mono-Si wafer had reflection Rmax= 92% and Rmax= 62% for multi-Si based BM. The control method of porous BM spectral response by pores filling with substance with a given refractive index was realized. It was shown that PS can be used as active material for photosensitive structures like Schottky barrier with quantum wells. The influence of the electrolyte parameters, the TiO2 layer porosity, and the illumination intensity on current through the porous TiO2 electrode of dispersive SC formed by electrophoresis deposition was determined. The presence of 2 class traps with activating energy ~220 (surface traps) and ~300 meV (deep traps) in TiO2 nanoparticles was determined by the thermostimulated polarization method. The effect of the negative differential conductivity in the n+-SnO2:F/nano-porous TiO2/InOHS/Au heterojunction is observed at room temperature. It was shown the current-voltage curve with the negative differential conductivity region, which appears on a positive branch after a negative voltage pulse, has been applied to the heterojunction. This in explained in a model of semiconductor (metal)-insulator-semiconductor with tunneling through deep electronic traps in por-TiO2.