Applying silicon solar cell technology to revolutionize the design of thin-film solar cells and enhance their efficiency, cost and stability

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Cu(In,Ga)Se2 based ultrathin solar cells: the pathway from lab rigid to large scale flexible technology

Publication . Lopes, Tomás; Teixeira, Jennifer; Curado, Marco; Ferreira, Bernado; Oliveira, Antonio; Cunha, José; Monteiro, Margarida; Violas, André; Barbosa, João; Sousa, Patricia; Çaha, Ihsan; Borme, Jérôme; Oliveira, Kevin; Ring, Johan; Chen, Wei; Zhou, Ye; Takei, Klara; Niemi, Esko; Francis, Leonard; Edoff, Marika; Brammertz, Guy; Fernandes, Paulo; Vermang, Bart; Salomé, Pedro

For the first time, the incorporation of interface passivation structures in ultrathin Cu(In,Ga)Se2 (CIGS) based solar cells is shown in a flexible lightweight stainless-steel substrate. The fabrication was based on an industry scalable lithography technique - nanoimprint lithography (NIL) - for a 15x15 cm2 dielectric layer patterning, needed to reduce optoelectronic losses at the rear interface. The nanopatterning schemes are usually developed by lithographic techniques or by processes with limited scalability and reproducibility (nanoparticle lift-off, spin-coating, etc). However, in this work the dielectric layer is patterned using NIL, a low cost, large area, high resolution, and high throughput technique. To assess the NIL performance, devices with a NIL nanopatterned dielectric layer are benchmarked against electron-beam lithography (EBL) patterning, using rigid substrates. Up to now, EBL is considered the most reliable technique for patterning laboratory samples. The device patterned by NIL shows similar light to power conversion efficiency average values compared to the EBL patterned device - 12.6 % vs 12.3 %, respectively - highlighting the NIL potential for application in the solar cell sector. Moreover, the impact of the lithographic processes, such as different etch by-products, in the rigid solar cells’ figures of merit were evaluated from an elemental point of view via X-ray Photoelectron Spectroscopy and electrically through a Solar Cell Capacitance Simulator (SCAPS) fitting procedure. After an optimised NIL process, the device on stainless-steel achieved an average power conversion efficiency value of 11.7 % - a slightly lower value than the one obtained for the rigid approach, due to additional challenges raised by processing and handling steel substrates, even though scanning transmission electron microscopy did not show any clear evidence of impurity diffusion towards the absorber. Notwithstanding, time-resolved photoluminescence results strongly suggested the presence of additional non-radiative recombination mechanisms in the stainless-steel absorber, which were not detected in the rigid solar cells, and are compatible with elemental diffusion from the substrate. Nevertheless, bending tests on the stainless-steel device demonstrated the mechanical stability of the CIGS-based device up to 500 bending cycles.

2022Journal article

Open access

Electronic Conduction Mechanisms and Defects in Polycrystalline Antimony Selenide

Publication . Cifuentes, N.; Ghosh, Santunu; Shongolova, A.; Correia, M. R.; Salomé, P. M. P.; Fernandes, P. A.; Ranjbar, S.; Garud, S.; Vermang, B.; Ribeiro, G. M.; González, J. C.

A study of the electronic conduction mechanisms and electrically active defects in polycrystalline Sb2Se3 is presented. It is shown that for temperatures above 200 K, the electrical transport is dominated by thermal emission of free holes, ionized from shallow acceptors, over the intergrain potential barriers. In this temperature range, the temperature dependence of the mobility of holes, limited by the intergrain potential barriers, is the main contributor to the observed thermal activation energy of the conductivity of 485 meV. However, at lower temperatures, nearest-neighbor and Mott variable range hopping transport in the bulk of the grains turn into the dominant conduction mechanisms. Important parameters of the electronic structure of the Sb2Se3 thin film such as the average intergrain potential barrier height ϕ = 391 meV, the intergrain trap density Nt = 3.4 × 1011 cm−2, the shallow acceptor ionization energy EA0 = 124 meV, the acceptor density NA = 1 × 1017 cm−3, the net donor density ND = 8.3 × 1016 cm−3, and the compensation ratio k = 0, 79 were determined from the analysis of these measurements.

2020-02-28Journal article

Restricted access