Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells

Abstract

As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO2) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H3PO4) etching, nitrogen (N2) gas anneal and forming gas (Ar: H2) anneal on the cells’ electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I–V, light I–V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.

Optical characterisation of silicon nanocrystals embedded in SiO2/Si3N4 hybrid matrix for third generation photovoltaics

“…The optical absorption properties of this kind of superlattices were investigated by a number of groups [12-14]. Photovoltaic diodes fabricated using similar approaches have been demonstrated by some of the present authors [5,6]. Their limitations include high device resistivity and the lower-than-expected output voltages.…”

Silicon quantum dot based solar cells: addressing the issues of doping, voltage and current transport

“…The data for the N 2 only anneal show that the improvement is not caused by heating alone. The data for different temperatures show that an increasing temperature of forming gas anneal up to 350°C increases the improvement 21. Further work on optimisation of annealing conditions and method (thermal or rapid thermal processing) is planned and expected to further improve V OC and I SC .…”

“… Hydrogen passivation: The 1‐sun light I – V characteristics of a Si QD cell following initial nitrogen (250°C) and consecutive H 2 forming gas anneals (250–350°C), showing increases in I SC and V OC on passivation with H 2 21. …”

Formation and photoluminescence of Si quantum dots in SiO2/Si3N4 hybrid matrix for all-Si tandem solar cells

“…As an important step towards the realization of silicon-based tandem solar cells using silicon quantum dots embedded in a dielectric matrix, we have fabricated single junction Si quantum dot solar cells with open-circuit voltage exceeding 400 mV [3,5]. This was based on Si nanocrystals embedded in a SiO 2 matrix.…”

“…(a) An all-Si quantum dot superlattice tandem solar cell[2], (b) a single junction Si QD solar cell with demonstrated voltage of more than 400 mV[3] and (c) the material system investigated in this work.…”