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.

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Photovoltaic materials: Present efficiencies and future challenges

First results showing the viability of combining laser chemical processing (LCP) and aerosol jet printing (AJP) technologies to produce a high-efficiency front side for silicon solar cells are presented. LCP simultaneously opens the anti-reflection coating (ARC) and highly dopes the underlying silicon to create a selective emitter, while AJP is the first in a two-step fine-line contact formation procedure. The electrical properties as well as the morphology of the resulting structures are presented. Performance similar to that achieved with evaporated TiPdAg metallization is demonstrated. Copyright © 2010 John Wiley & Sons, Ltd.

Combining laser chemical processing and aerosol jet printing: a laboratory scale feasibility study

In order to improve the solar cell efficiency of the solar cell concept of interest most efficiently, it is essential to analyze its loss mechanisms. Numerical simulations are used to calculate the individual solar cell loss mechanisms. The calculated current losses can be used to identify the main losses and can give recommendation for the next improvement steps. We present a method for a current density loss analysis of crystalline silicon solar cells based on 2-D and 3-D numerical simulations. With the presented method, a collection of relevant crystalline silicon solar cell concepts are investigated. By determining the main loss mechanisms of each cell concept, the limitations and the potential of the different concepts are pointed out.

Numerical Current Density Loss Analysis of Industrially Relevant Crystalline Silicon Solar Cell Concepts

Inline Processes for the Stabilization of p-Type Crystalline Si Solar Cells Against Potential-Induced Degradation

As solar cell production grows with record rates of approximately 30-40 % per year for the last 5 years the market starts 
to awake interest at various industries. Especially the laser technology seems to gain influence on the production 
sequence as more sophisticated solar cell concepts like laser-fired contacts (LFC), metal- / emitter-wrap through cells 
(MWT /EWT) or back junction solar cells are about to be industrially applicable. This paper gives a short introduction 
over the current situation of the solar cell market and the state of the art technology. Furthermore future cell concepts 
are explained briefly, where the main focus is set on the chances for laser technology to be implemented. Additionally 
the specific demands of the solar cell production are mentioned and all potentially possible laser processes rated with 
respect to their potential of being transferred into industry.

Laser applications in crystalline silicon solar cell production

In this paper, we introduce a new kind of hybrid concentrator photovoltaic module that is capable of harvesting direct and diffuse irradiance. The concept, denominated EyeCon, uses a Fresnel lens to concentrate direct irradiance onto a primary III–V four-junction solar cell. Directly underneath, a large-area silicon cell is stacked and used as a secondary conversion material for diffuse irradiance while also acting as a heat distributor. This paper focuses on determining the feasibility of this concept based on the evaluation of the thermal behavior of both cells. Such assessment is performed using finite element analysis, indoor infrared thermography, and outdoor measurements under real concentrator operating conditions. The results reveal that under an ambient temperature of 25 °C and a geometric concentration of 226 × 900 W/m2 plus 100 W/m2 of diffuse irradiance, the concentrator III–V and silicon cell temperatures do not increase beyond 80 °C and 60 °C, respectively. Thus, our analysis shows that the silicon can be used simultaneously as a heat distributor and a solar cell.

Stefan W. Glunz

Papers

Combining laser chemical processing and aerosol jet printing: a laboratory scale feasibility study

Numerical Current Density Loss Analysis of Industrially Relevant Crystalline Silicon Solar Cell Concepts

Inline Processes for the Stabilization of p-Type Crystalline Si Solar Cells Against Potential-Induced Degradation

Laser applications in crystalline silicon solar cell production

Thermal Analysis of Passively Cooled Hybrid CPV Module Using Si Cell as Heat Distributor