Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting....

Polymers for 3D Printing and Customized Additive Manufacturing

The efficiency of silicon solar cells has a large influence on the cost of most photovoltaics panels. Here, researchers from Kaneka present a silicon heterojunction with interdigitated back contacts reaching an efficiency of 26.3% and provide a detailed loss analysis to guide further developments.

Silicon heterojunction solar cell with interdigitated back contacts for a photoconversion efficiency over 26

The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Perovskite solar cells typically comprise electron- and hole-transport materials deposited on each side of a perovskite active layer. So far, only two organic hole-transport materials have led to state-of-the-art performance in these solar cells1: poly(triarylamine) (PTAA)2–5 and 2,2ʹ,7,7ʹ-tetrakis(N,N-di-p-methoxyphenylamine)-9,9ʹ-spirobifluorene (spiro-OMeTAD)6,7. However, these materials have several drawbacks in terms of commercialization, including high cost8, the need for hygroscopic dopants that trigger degradation of the perovskite layer9 and limitations in their deposition processes10. Poly(3-hexylthiophene) (P3HT) is an alternative hole-transport material with excellent optoelectronic properties11–13, low cost8,14 and ease of fabrication15–18, but so far the efficiencies of perovskite solar cells using P3HT have reached only around 16 per cent19. Here we propose a device architecture for highly efficient perovskite solar cells that use P3HT as a hole-transport material without any dopants. A thin layer of wide-bandgap halide perovskite is formed on top of the narrow-bandgap light-absorbing layer by an in situ reaction of n-hexyl trimethyl ammonium bromide on the perovskite surface. Our device has a certified power conversion efficiency of 22.7 per cent with hysteresis of ±0.51 per cent; exhibits good stability at 85 per cent relative humidity without encapsulation; and upon encapsulation demonstrates long-term operational stability for 1,370 hours under 1-Sun illumination at room temperature, maintaining 95 per cent of the initial efficiency. We extend our platform to large-area modules (24.97 square centimetres)—which are fabricated using a scalable bar-coating method for the deposition of P3HT—and achieve a power conversion efficiency of 16.0 per cent. Realizing the potential of P3HT as a hole-transport material by using a wide-bandgap halide could be a valuable direction for perovskite solar-cell research. A double-layered halide architecture for perovskite solar cells enables the use of dopant-free poly(3-hexylthiophene) as a hole-transport material, forming stable and scalable devices with a certified power conversion efficiency of 22.7 per cent.

Efficient, stable and scalable perovskite solar cells using poly(3-hexylthiophene)

Recent developments in photovoltaic materials have led to continual improvements in their efficiency. We review the electrical characteristics of 16 widely studied geometries of photovoltaic materials with efficiencies of 10 to 29%. Comparison of these characteristics to the fundamental limits based on the Shockley-Queisser detailed-balance model provides a basis for identifying the key limiting factors, related to efficient light management and charge carrier collection, for these materials. Prospects for practical application and large-area fabrication are discussed for each material.

/pdf/photovoltaic-materials-present-efficiencies-and-future-3yblyv6m8p.pdf

Photovoltaic materials: Present efficiencies and future challenges

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pip.3503

Two‐terminal III–V//Si triple‐junction solar cell with power conversion efficiency of 35.9 % at AM1.5g

We have investigated the effect of the light-induced deep-level recombination centre specific to boron-doped, oxygen-contaminated Czochralski (Cz) silicon on the current-voltage characteristic of Cz silicon solar cells by means of numerical simulation and experiment. The device simulation predicts the occurrence of a shoulder in the current-voltage curve after activating the characteristic recombination centre. The physical reason for the non-ideal diode behaviour, characterised by a local ideality factor greater unity, is the strongly injection-level-dependent bulk lifetime produced by the deep-level centre. The increased ideality factor causes a degradation in fill factor with the magnitude of degradation depending on the doping concentration of the Cz silicon base. In order to verify the theoretical predictions experimentally, we have performed measurements on high-efficiency Cz silicon solar cells. Current-voltage curves recorded before and after light degradation clearly show the theoretically predicted change in shape and the reduction in fill factor. An excellent quantitative agreement between calculation and experiment is obtained for the subtracted current-voltage curves measured after and before illumination.

Impact of light‐induced recombination centres on the current–voltage characteristic of czochralski silicon solar cells

Fraunhofer ISE's concept for an advanced metallization of silicon solar cells is based on a two-step process: the deposition of a seed layer to form a mechanical and electrical contact and the subsequent thickening of this seed layer by a plating step, preferably by light-induced plating (LIP). The concept of a multi-layer metallization is used for most of the relevant high-efficiency cell types in industry. The main advantage of this concept is that each layer can be optimized individually, i.e. the seed layer to achieve an optimal electrical and mechanical contact and the plated layer in terms of high lateral conductivity and good solderability. Solar cells results with seed layers fabricated by aerosol printing, chemical Ni plating on cells with a laser-structured dielectric layer and laser-enhanced Ni plating are presented.

Progress in advanced metallization technology at Fraunhofer ISE

Beschrieben wird ein Verfahren zur elektrischen Kontaktierung einer, mit wenigstens einer dielektrischen Schicht (12) uberzogenen Halbleiterschicht (13). Die Erfindung zeichnet sich dadurch aus, dass eine Metallschicht (11) auf die dielektrische Schicht (12) aufgebracht wird und mittels einer Strahlungsquelle (9) diese Metallschicht (11) kurzzeitig lokal punkt- oder linienformig derart kontrolliert erhitzt wird, so dass sich eine lokale Schmelzmischung ausschliesslich aus der Metallschicht (11), der dielektrischen Schicht (12) sowie der unmittelbar unter der dielektrischen Schicht (12) befindlichen Halbleiterschicht (13) ausbildet, die nach dem Erstarren zu einem elektrischen Kontakt zwischen der Halbleiterschicht (13) und der Metallschicht (11) fuhrt.

Verfahren zur herstellung eines halbleiter-metallkontaktes durch eine dielektrische schicht

TOPCon is an appealing choice for next-generation solar cells as it minimizes surface recombination, enables low contact resistivities, and provides high thermal stability thereby rendering it compatible with screenprinted metallization. While TOPCon is commonly realized by low-pressure chemical vapor deposition (LPCVD), this paper discusses the use of a plasma-enhanced chemical vapor deposition (PECVD) tool, which are commonly used for deposition of SiNx or AlOx. It will be shown that thick screen-printing compatible TOPCon layers providing excellent surface passivation can be realized with such tool. Additionally, the firing stability of TOPCon/SiNx stack will be discussed and first solar cell results will be presented. The IV parameters of the best solar cell were: Voc = 691.2 mV, FF = 80.7%, Jsc = 40.4 mA/cm2, and η = 22.5%.

Stefan W. Glunz

Papers

Two‐terminal III–V//Si triple‐junction solar cell with power conversion efficiency of 35.9 % at AM1.5g

Impact of light‐induced recombination centres on the current–voltage characteristic of czochralski silicon solar cells

Progress in advanced metallization technology at Fraunhofer ISE

Verfahren zur herstellung eines halbleiter-metallkontaktes durch eine dielektrische schicht

Large Area TOPCon Cells Realized by a PECVD Tube Process