Electronic states in a Si H c Si heterostructures

Electronic states in a Si H c Si heterostructure

Improvement of silicon solar cell substrates by wet chemical oxidation studied by surface photovoltage measurements

Conventional strategies for wet chemical pre treatment are mainly based on concentrated solutions. Electronic interface properties can be enhanced by opti mised sequences of surface oxidation in concentrated acids e.g. RCA I and II , H2SO4 H2O2, HNO3 68 and etching in HF containing solutions NH4F 40 or HF 1 . To minimise chemical consumption and the number of process steps, in this study also mixtures of ultra pure deionized water DiW with dissolved ozone O3 [ ] or hy drochloric acid HCl [ ] were investigated as an alternative to RCA, HNO3 and H2SO4 H2O2 solutions. The aim of these investigations is to reach the comparable cleaning and passivation ef fects, as achieved by conventional concentrated solutions, with a significant cost reduction. According to our results wet chemical oxidation in diluted solutions of HCl [9] or ozone O3 [4] could be a high quality and low cost alternative to current approaches with liquid chemicals for the preparation of hydrophobic Si substrate surfaces and ultra thin passivating oxide layers

Recombination analysis at the n doped a Si H n c Si p heterojunction by means of time and intensity dependent surface photovoltage

Recombination analysis at the n doped a Si H n c Si p heterojunction by means of time and intensity dependent surface photovoltag

Electronic key quantities of a Si H n,p C Si p,n heterostructure solar cells

Electronic key quantities of a Si H n,p c Si p,n heterostructure solar cell

Characterization of interfaces in amorphous crystalline silicon heterojunction solar cells by surface photovoltage spectroscopy

Characterization of Interfaces in Amorphous Crystalline Silicon Heterojunction Solar Cells by Surface Photovoltage Spectroscop

Surface photovoltage investigation of recombination at the a Si c Si heterojunction

We investigate the use of time resolved surface photovoltage SPV transients as a means to determine band bending and recombination properties at amorphous crystalline silicon a Si H c Si heterojunctions. Experimentally, it is shown that for a Si H film thicknesses above 6 nm, SPV transients do not depend on the film thickness anymore. On this basis, a simple numerical model is proposed that consists of a single rechargeable gap state on the c Si wafer surface, into which the properties of the a Si H c Si interface and the adjacent a Si H are lumped. It is shown that this model can reproduce all principal features of high excitation SPV transients, i.e. an initial fast decay shown to be due to Auger recombination, a plateau region for high injection conditions and a fast decay when the sample returns into low injection and the defect states are recharged. Under sufficiently high excitation, the SPV saturates at a value that is determined by the a Si H c Si interface band bending in the dark. From the slope of the transient decay, defect parameters density, energetic position can be extracte

Wet chemical preparation of textured silicon solar cell substrates Surface conditioning and electronic interface properties

Decisive preconditions to the development of economically attractive solar cells are further improvements of the energy conversion efficiency by appropriate interface preparation and passivation meth ods as well as the reduction of material consumption by the application of thin film technologies [ ]. For this purpose also the simplification of technological proc esses, particularly the suitability and cost effectiveness of wet chemical cleaning and etching processes has to be taken carefully into consideration. This paper reports on the investigation of wet chemical etching und surface conditioning of different Si sub strates, carried out before preparation of thin oxides, amorphous crystalline a Si H c Si hetero junctions, Si nitride a SiNx H passivation layers and contacts.The relation between structural imperfections at Si surfaces, light trapping behavior, interface state densi ties and recombination losses was investigated by scan ning electron microscopy SEM , surface photovoltage SPV [5], microwave detected photo conductance decay W PCD [ ], quasi steady state photo conduc tance QSSPC , and UV NIR reflectance measure ments [ ]. Electronic interface properties of textured Si substrates for solar cells application were found to be mainly influenced by the crystallographic surface configuration of light trapping structures and secondly, the effective ness of wet chemical smoothing, H termination or oxidation procedures. Strong effects of surface conditioning were found on c Si a Si H, on Si carbide a SiC H and also on c Si a SiNx H interfaces, even though the field effect passivation is based on the band bending caused by a fixed charge in the fil

Wet chemical oxidation of silicon surfaces prior to the deposition of all PECVD AlOx a SiNx passivation stacks for silicon solar cells

AlOx films contain negative charges and therefore generate an accumulation layer on p type silicon surfaces, which is very favorable for the rear side of p type silicon solar cells as well as the p emitter at the front side of n type silicon solar cells. However, it has been reported that quality of an interfacial silicon sub oxide layer SiOx , which is usually observed during deposition of AlOx on Silicon, strongly impacts the silicon AlOx interface passivation properties [1]. The present work demonstrates that a convenient way to control the interface is to form thin wet chemical oxides of high quality prior to the deposition of AlOx a SiNx H stacks by the plasma enhanced chemical vapor deposition PECVD . To evaluate quantitatively the effect of the preconditioning steps, we conducted measurements of the interface state density Dit E by means of the surface photovoltage technique immediately after the wet chemically preconditioned surfaces. The work has demonstrated that wet chemical oxides with low manufacturing costs can be used to improve the passivation quality of PECVD deposited AlOx a SiNx H stacks. An important contribution to the high level of passivation of the SiOx AlOx a SiNx H stacks after post deposition thermal steps is attributed to improved interface properties controlled by the Si O Si bonding structure and saturation of recombination centers by hydroge