27 Jun 2013

Tuning the band gap of CZT(S,Se) nanocrystals by anion substitution

Literature Discussion

Submitted by Benny Chan, The College of New Jersey

The paper from the Prieto group, Riha, S. C.; Parkinson, B. A.; Prieto, A. L. J. Am. Chem. Soc. 2011, 133, 15272-15275, is proposed to be an excellent literature article for achieving several learning goals in the understanding of fundamental solid state and materials chemistry. The learning object was developed as a part of the 2013 VIPEr workshop and has not been tested in the classroom. We have developed a set of discussion questions that can be used as a guide for the students. We have also developed a complementary LO, that uses a concept map to help understand the article. We provide additional questions for assessing the concept map. We would appreciate help in testing the effectiveness of the discussion questions with and without the concept map.

The paper in discussion describes the synthesis of CZT(S, Se) nanoparticles that have potential application in the manufacturing of low-cost and environmentally responsible thin-film solar cells. The article reviews the previous literature and explicitly develops testable hypotheses. The as-synthesized nanoparticles are carefully studied by a suite of instrumental techniques including X-ray diffraction, high resolution transmission electron microscopy, and UV-vis spectroscopy. The data from the paper can be used to help students understand the synthesis, characterization, and properties of semiconducting nanomaterials. Furthermore, the paper explains the implications of their finding to further the scientific study of multicomponent chalcogenide nanocrystals.

File Discussion LO Student.docx131.42 KB
Learning Goals: 

LG1: Find a specific scholarly article and its supporting information from a library resource.

LG2: Explain the effects of solid solution formation on material properties including changes in the empirical formula, unit cell, lattice parameters, and energy band gap.

LG3: Compare multiple analytical techniques that are needed to complete a scientific study.

LG4: Use data to justify the goals of the article.

LG5: List the advantages and disadvantages of CZT(S,Se) nanoparticles as components in next generation photovoltaic devices.

LG6: Evaluate the usefulness of a concept map to connect multiple ideas in this primary literature article.

Implementation Notes: 

We have not attempted to implement this LO.  We imagine that this LO could be used in conjunction with the concept map LO.  We would assume that students could work in small groups to discuss the literature.


Evaluation Methods: 

We have not attempted to evaluate this LO.  As we use the LO, we will post the assessment data.

The writers of this LO also wanted to assess the effectiveness of the Concept Map LO of this article (Linked on website) when answering the same set of questions.  We want to assess whether concept mapping of the article would aid in the comprehension of a literature article.  If the students have a measureable increase in understanding, we believe concept mapping an article would be a good, transferable strategy for students to dissect and to understand an article.  


Creative Commons License: 
Creative Commons Licence


I used this literature discussion in my 2nd semester general chemistry course with 70 students this past Spring. I wrote a VIPEr BITeS blog post about it recently (https://www.ionicviper.org/blog-entry/tues-2013-workshop-los-action), but wanted to give a bit more detail about the students’ response and assessment here.

As I mentioned in the blog post, most of the students taking this class are 2nd semester sophomores. I covered unit cells, solid solutions, techniques (EDS, powder X-ray diffraction), and band theory in the classes leading up to the lit discussion. I had students sign up for a 25-min discussion group using a Doodle poll; groups were limited in size to 15. Students were asked to read the paper and bring in responses to the lit discussion questions. During discussion groups, we went over the answers to the questions. Overall, students did well with the discussion questions. Some had difficulty examining the structure of kesterite from the Wikipedia figure (question 3), and as the techniques in the paper were new to the students, we needed to spend a fair amount of time going over questions 4-6 as well.

In terms of assessment, I asked one 25-point question on the final exam related to topics in the paper. Students were asked to explain what a solid solution is (10 points), predict what would happen to the band gap and PXRD if someone started with CZTSe nanoparticles and substituted Te for Se (10 points, adapted from the suggested assessment problem in this LO), and to name a technique to measure the composition of elements for the new Te containing nanoparticles (5 points). 26% of the class got a perfect score on this question, another 33% scored between 80-99%, and only 21% of the class scored below 50% on this question. Thus, with 59% of the class scoring 80% or above, and an average score on this question of 73%, I felt as though the students demonstrated a reasonable mastery of the concepts from the paper.

In addition, I asked the class to fill out a survey about this activity in exchange for 4 bonus points on the final exam; 58 students responded. Looking over the results, only 17% of the class reported that they didn’t understand the article well when they read it. 74% of the class reported that the class lectures were helpful/very helpful in preparing them to read the article. 53% of the class reported that the small group discussions were useful/very useful, with 16% not finding the discussion groups useful. Encouragingly, 78% of the class said that it was important/very important to see a "real life" literature example of solid state chemistry, with 53% recommending definitely doing this activity again (another 45% recommended possibly doing it again – but with some improvements).

32 students left a response in the optional open comment part of the survey. One of the most striking things to me was that 25% of the students commented on how they would have liked to have spent more time discussing the article and going over the discussion questions. Another common remark (16% of comments) was that students would have liked to have done an activity like this for some of the other topics covered in class.

Thus, while this experiment with a lit discussion in a class of 70 students wasn’t perfect, I do think it was successful enough for me to want to repeat it at some point in the future with some modifications. The students’ enthusiasm for seeing a “real life” example is clear and highlights the need for us to have more LOs like this one that showcase current research in inorganic chemistry.

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