With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

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High-efficiency crystalline silicon solar cells: status and perspectives

Photovoltaic solar cells based on metal halide perovskites have gained considerable attention over the past decade because of their potentially low production cost, earth-abundant raw materials, ease of fabrication and ever-increasing power conversion efficiencies of up to 25.2%. This type of solar cells offers the promise of generating electricity at a more competitive unit price than traditional fossil fuels by 2035. Nevertheless, the best research cell efficiencies are still below the theoretical limit defined by the Shockley-Queissier theory owing to the presence of non-radiative recombination losses. In this Review, we analyse the predominant pathways that contribute to non-radiative recombination losses in perovskite solar cells, and evaluate their impact on device performance. We then discuss how non-radiative recombination losses can be estimated through reliable characterization techniques, and highlight some notable advances in mitigating these losses, which hint at pathways towards defect-free perovskite solar cells. Finally, we outline directions for future work that will push the efficiency of perovskite solar cells towards the radiative limit.

Minimizing non-radiative recombination losses in perovskite solar cells

Negative thermal expansion (NTE) is an intriguing physical property of solids, which is a consequence of a complex interplay among the lattice, phonons, and electrons. Interestingly, a large number of NTE materials have been found in various types of functional materials. In the last two decades good progress has been achieved to discover new phenomena and mechanisms of NTE. In the present review article, NTE is reviewed in functional materials of ferroelectrics, magnetics, multiferroics, superconductors, temperature-induced electron configuration change and so on. Zero thermal expansion (ZTE) of functional materials is emphasized due to the importance for practical applications. The NTE functional materials present a general physical picture to reveal a strong coupling role between physical properties and NTE. There is a general nature of NTE for both ferroelectrics and magnetics, in which NTE is determined by either ferroelectric order or magnetic one. In NTE functional materials, a multi-way to control thermal expansion can be established through the coupling roles of ferroelectricity-NTE, magnetism-NTE, change of electron configuration-NTE, open-framework-NTE, and so on. Chemical modification has been proved to be an effective method to control thermal expansion. Finally, challenges and questions are discussed for the development of NTE materials. There remains a challenge to discover a “perfect” NTE material for each specific application for chemists. The future studies on NTE functional materials will definitely promote the development of NTE materials.

Negative thermal expansion in functional materials: controllable thermal expansion by chemical modifications

Recent Progresses on Defect Passivation toward Efficient Perovskite Solar Cells

Metal-halide perovskites are rapidly emerging as an important class of photovoltaic absorbers that may enable high-performance solar cells at affordable cost. Thanks to the appealing optoelectronic properties of these materials, tremendous progress has been reported in the last few years in terms of power conversion efficiencies (PCE) of perovskite solar cells (PSCs), now with record values in excess of 24%. Nevertheless, the crystalline lattice of perovskites often includes defects, such as interstitials, vacancies, and impurities; at the grain boundaries and surfaces, dangling bonds can also be present, which all contribute to nonradiative recombination of photo-carriers. On device level, such recombination undesirably inflates the open-circuit voltage deficit, acting thus as a significant roadblock toward the theoretical efficiency limit of 30%. Herein, the focus is on the origin of the various voltage-limiting mechanisms in PSCs, and possible mitigation strategies are discussed. Contact passivation schemes and the effect of such methods on the reduction of hysteresis are described. Furthermore, several strategies that demonstrate how passivating contacts can increase the stability of PSCs are elucidated. Finally, the remaining key challenges in contact design are prioritized and an outlook on how passivating contacts will contribute to further the progress toward market readiness of high-efficiency PSCs is presented.

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Defect and Contact Passivation for Perovskite Solar Cells.

https://openresearch-repository.anu.edu.au/bitstream/1885/13664/1/Fell%20A%20et%20al%20Quantitative%20surface%20recombination%202014.pdf

Quantitative Surface Recombination Imaging of Single Side Processed Silicon Wafers Obtained by Photoluminescence Modeling

Carbon doped YAG (YAG : C) crystal is designed and grown by the temperature gradient technique, and the optical and optically stimulated luminescence (OSL) properties of the as-grown crystal are investigated. High concentration F+-centres with an emission at 400 nm are produced in the YAG crystal by the introduction of carbon. The as-grown YAG : C shows high OSL sensitivity and excellent OSL response thermal stability up to 573 K. In the wide dose range from 0.1 to 50 Gy, the OSL response shows excellent linearity, and saturation is found at about 200 Gy. Almost no light-induced fading is observed in the YAG : C crystal when exposed in the dark.

The optically stimulated luminescence of carbon doped Y3Al5O12 (YAG) crystal

J.K., X.Y., and W.L. contributed equally to this work. Xinyu Zhang is thanked for Raman spectroscopy characterizations and Mohamed Nejib Hedhili for XPS measurement. This work was supported by funding from King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under award no. OSR-CRGURF/1/3383.

Electron-Selective Lithium Contacts for Crystalline Silicon Solar Cells

J.K. and W.L. contributed equally to this work. This work was supported by funding from King Abdullah University of Science and Technology (KAUST) Oce of Sponsored Research (OSR) under award no. OSR-CRG URF/1/3383.

Xinbo Yang

Papers

Quantitative Surface Recombination Imaging of Single Side Processed Silicon Wafers Obtained by Photoluminescence Modeling

The optically stimulated luminescence of carbon doped Y3Al5O12 (YAG) crystal

Electron-Selective Lithium Contacts for Crystalline Silicon Solar Cells

Intrinsic Silicon Buffer Layer Improves Hole-Collecting Poly-Si Passivating Contact

Simulation of 20.96% Efficiency n-type Czochralski UMG Silicon Solar Cell