Showing posts with label paper. Show all posts
Showing posts with label paper. Show all posts

October 15, 2019

How to read a scientific paper in just three steps

Reading on paper is an old school way to annotate
and highlight the most interesting elements
For a scientist, reading is a must responsibility in the modern world of information, this task allows us to update the state of the art of the current research. For example, the objective of my work is to reproduce and improve antimony sulfo-selenide thin-film solar cells. Therefore, the first thing I did before experimental research It was to read the updated literature. As I am in touch with the author of the paper of interest I asked him about it's last published paper where their group develops Sb-S-Se photovoltaic mini-module prototypes. 

P.K. Nair*, J.D.G. Sánchez, L.G. Martínez, P.Y.G. Ayala, A.K.M. Peñaloza, A.B. León, Y.C. García, J. Campos Álvarez, M.T.S. Nair, Chemically Deposited Antimony Sulfide Selenide Thin Film Photovoltaic Prototype Modules, ECS J. Solid State Sci. Technol. 8 (2019) Q89–Q95. doi:10.1149/2.0101906jss.

To fully understand, I almost read a scientific paper three times:

  • First: Print it or read it on PDF (Mendeley could help), the important thing here is to read from the beginning to the end as soon as possible.
  • Second: Make annotations for later discussion and highlights from the most important elements you can find on the text.
  • Third: Write a resume, this will allow you to save the essential information in the same notebook of literature review. I prefer to write it on the Blogspot or a note on the Evernote app following the next template.

Read more, to discover the structure or template for paper review, here you are going to write just the notes and highlighted parts. This is my way to learn fast. If you have an alternate strategy please feel free to share it in the comments section.

October 14, 2019

Paper: Chemically deposited antimony sulfide selenide thin film photovoltaic prototype modules

Authors: P. K. Nair,  José Diego Gonzaga Sánchez, Laura Guerrero Martínez, Perla Yoloxóchitl García Ayala, Ana Karen Martínez Peñaloza, Alessandra Beauregard León, Yareli Colín García, José Campos Álvarez, and M. T. S. Nair

Link: ECS Journal of Solid State Science and Technology, 8 (6) Q89-Q95 (2019)


We present thin film antimony sulfide selenide prototype photovoltaic modules of area, seven cm2 and conversion efficiency (η) of 3.5%. The thin films of Sb2SxSe3-x (x, 0.8–1.6) of 120–180 nm in thickness were deposited on FTO/CdS(80 nm) substrates at 80°C from chemical bath containing potassium antimony tartrate, thioacetamide and sodium selenosulfate. Thin film of CdS of 80 nm in thickness was deposited from a chemical bath at 80°C during 65 min on fluorine-doped SnO2 (FTO). The solar cell structure FTO/CdS/Sb2SxSe3-x/C had colloidal graphite paint of area, 0.7 cm× 0.7 cm. This cell structure was heated at 300°C during 30 min in a nitrogen ambient to create a carbon-doped antimony chalcogenide layer. Silver paint was applied to the carbon electrode and on FTO around it. Prototype modules had seven series connected cells of one cm2 each with a total area of seven cm2. Solar cell with varying composition of Sb2SxSe3-x along its thickness had a η of 3.88% at an open circuit voltage (Voc) of 0.44 V and short circuit current density of 18.3 mA/cm2. Prototype modules lighted-up blue light emitting diodes at a power, 5–15 mW.


  • The best solar cell is:   Voc = 441 mV, Jsc = 18.34 mA/cm2, FF = 0.48 and efficiency = 3.88 % measured under standar conditions of 1 sun (Solar simulator). 
  • Application of carbon paint over chalcogenide layer and subsequent heating of the entire cell structure would create a carbon-doped antimony chalcogenide layer

Device fabrication 
  • Substrate:  TEC7 
  • Window layer:  CdS by chemical deposition (80 nm)
  • Absorber layer: Sb-S-Se by sequential chemical deposition  (180 nm)
  • Back contact: Graphite paint (SPI) / Silver paint (N2 heat treatment, 300 ºC) 

Characterization techniques 

  • EDS - Over finished solar cells 
  • GIXRD - Over solar cell 
  • T and R - Optical  for calculation of absorption coefficient, bandgap  and photogenerated current (JL) 
  • JC curve for solar cell and mini-modules
  • EQE for solar cells 


  • This work is open for improvements in all the constitutive components of the solar cell device. 

April 23, 2019

Paper: Complex Interplay between Absorber Composition and Alkali Doping in High-Efficiency Kesterite Solar Cells

Title: Complex Interplay between Absorber Composition and Alkali Doping in High-Efficiency Kesterite Solar Cells
Authors: Stefan G. Haass,* Christian Andres, Renato Figi, Claudia Schreiner, Melanie Bürki, Yaroslav E. Romanyuk, and Ayodhya N. Tiwari
Link (Open Acess): Adv. Energy Mater. 2018, 8, 1701760

Sodium treatment of kesterite layers is a widely used and efficient method to boost solar cell efficiency. However, first experiments employing other alkali elements cause confusion as reported results contradict each other. In this comprehensive investigation, the effects of absorber composition, alkali element, and concentration on optoelectronic properties and device performance are investigated. Experimental results show that in the row Li–Na–K–Rb–Cs the nominal Sn content should be reduced by more than 20% (relative) to achieve the highest conversion efficiency. The alkali concentration resulting in highest device efficiencies is lower by an order of magnitude for the heavy alkali elements (Rb, Cs) compared to the lighter ones (Li, Na, K). Utilization of a wide range of characterization techniques helps to unveil the complex interplay between absorber composition and alkali doping. A ranking of alkali for best device performances, when employing alkali treatment, resulted in the order of Li > Na > K > Rb > Cs based on the statistics of more than 700 individual cells. Finally, a champion device with 11.5% efficiency (12.3% active area) is achieved using a high Li concentration with an optimized Sn content.

  • Best published solar cell CZTSe: 12.6 % by IBM and DGIST (0.4 - 0.5 cm2 active area)
  • Solution process deposition technique [14]
  • The secondary phase Sn(S,Se)2 can be identify from XRD when Sn nominal content is > 33.3% 
  • The formation of the second phase tin selenide is influenced by the type of concentration of alkali elements 
  • Minority carriers trapping, surface effects and energetic relaxation of carriers has been identified to severely affect the PL transition times. Thus the measurement of transition decay times does not represent the real minority carriers lifetime in the kesterite absorber layer. 
    • The champion solar cell has high Li content (3.3%) and 33.3% of Sn nominal concentration of 33.3 %.  11.55 % with metal electrodes and 12.3 without a metal grid. Area = 0.29 cm2. 
  • A ranking of best device performances employing alkali treatment resulted in the order of Li > Na > K > Rb > Cs based on the statistics of more than 700 individual cells. 
Characterization techniques: 

  • ICP-MS (Inductively coupled plasma-mass spectroscopy), detect alkali content in the absorber layer.
  • SEM (Scanning electron microscopy)
  • XRD (X-ray diffraction): To understand the device performance reduction at high Sn content
  • XRF (X-ray fluorescence)
Solar cell 
  • JV (current-voltage)
  • C-V (capacitance-voltage): Apparent carrier concentration and depletion region width.
  • TRPL (Time-resolved photoluminescence): 639 nm pulse diode laser , 90ps pulse width and 10 MHz 
  • EQE (External quantum efficiency)

April 22, 2019

Paper: How small amounts of Ge modify the formation pathways and crystallization of kesterites

Ge incorporation on Kesterites

How small amounts of Ge modify the formation pathways and crystallization of kesterites
Authors: S. Giraldo, E. Saucedo, M. Neuschitzer, F. Oliva, M. Placidi, X. Alcobe´, V. Izquierdo-Roca, S. Kim, H. Tampo, H. Shibata, A. Pérez-Rodríguez and P. Pistor

Link: Energy Environ. Sci., 2018, 11, 582-593


The inclusion of Ge into the synthesis of Cu2ZnSn(S,Se)4 absorbers for kesterite solar cells has been proven to be a very efficient way to boost the device efficiency in a couple of recent publications. This highlights the importance to elucidate the mechanisms by which Ge improves the kesterite solar cells properties to such a large extent. In this contribution, we first show how controlling the position and thickness of a very thin (10–15 nm) layer of Ge greatly influences the crystallization of kesterite thin films prepared in a sequential process. Typically, Cu2ZnSnSe4 (CZTSe) films form in a bi-layer structure with large grains in the upper region and small grains at the back. By introducing Ge nanolayers below our precursors, we observe that large CZTSe grains extending over the whole absorber thickness are formed. Additionally, we observe that Ge induces fundamental changes in the formation mechanism of the kesterite absorber. In a detailed analysis of the phase evolution with and without Ge, we combine the results of X-ray fluorescence, X-ray diffraction, and Raman spectroscopy to demonstrate how the Ge influences the preferred reaction scheme during the selenization. We reveal that the presence of Ge causes a large change in the in-depth elemental distribution, induces a stabilizing Cu–Sn intermixing, and thus prevents drastic compositional fluctuations during the annealing process. This finally leads to a change from a tri-molecular towards, mainly, a bi-molecular CZTSe formation mechanism. Kesterite thin films with surprisingly large crystals of several microns in diameter can be fabricated using this approach. The results are related to the increase in device performance, where power conversion efficiencies of up to 11.8% were obtained. Finally, the consequences of the disclosed crystallization pathways and the extension to other chalcogenide technologies are discussed


  • Kesterite solar cell record efficiency of 12.6% (2018) [1]
  • Advantages like earth abundant and non-toxic materials of CZTSe will success if the technology reaches 20% efficiency and be ready for industrial manufacturing. 
  • Disadvantages: Low Voc (Open circuit voltage is an indirect measurement of the recombination process of the solar cell, following Shockley design). 
    • Potential fluctuations
    • Band tailing
    • Disorder defects 
    • Interface recombination 
    • Secondary phases 
    • Compositional inhomogeneities
  • The presence of Ge drastically modifies the reaction pathway in which the kesterite is formed
  • The beneficial effects of Ge incorporation are not limited to some surface modifications it affects the whole bulk of the absorber. 
  • The observed improvement should be located on the absorber bulk due to an increase in the charge carrier lifetime. 

Characterization Techniques:

  • Materials
    • SEM (5 keV) 
    • Thickness by SEM (2µm of the absorber layer)
    • EDX (20 kV)
    • XRS (Brag-Brentano configuration, 4-145º, step 0.017º, )
    • Raman (excitation wavelengths: 633 nm, 532 nm, 488 nm )
    • XRF (X-ray fluorescence) to determine overall composition and thickness
  • Solar cell
    • JV curve (Standard parameters)
    • EQE (Increase due optimization at the bulk of the absorber)
    • Voc vs T  (Activation Energy of recombination process)

Relevant information:

  • Heat treatment to induce grain growth is crucial for a better solar cell. Then Ge assisted crystallization process affect the whole bulk absorber. 
  • Goal: Increase Voc on the device is the challenge to increase efficiency > 12%. 
  • Goal: Detect the dominant recombination mechanism.

Disclaimer: The intention of this post is to bring some personal notes of the literature review. I'm not sharing the PDF files. For that purpose, please ask the authors or follow the link to the journal.