Talking about strategies for high efficiency kesterite solar cells

Dr. Edgardo A. Saucedo visits BUAP after the MRS congress in Cancun, Mexico and gives us a motivational talk about kesterites PV technology. He is the leader of the Solar Energy Materials and Systems Group at IREC and leads the European STARCELL project too.

 Kesterites are a promising PV material, it's metal elements, Copper, Zinc, and Tin are abundant on earth crust. This material owns a tetragonal lattice similar to commercial PV technology. As Dr. Saucedo said, they come from the royal family of photovoltaics. 

Kesterites comes from the royal family of photovoltaics

Source: PV-Education Crystal structure of the royal family of photovoltaics

The pace of research on kesterites has been slow due to the emergence of perovskites who has reached a conversion efficiency of 24%(early 2019) while kesterite holds a record of 12.6% reported by IBM in 2013. As you can see, there is a difference of 6 years between both reports [1].

STARCELL born to push forward kesterites PV technology and it is formed by universities and industrial partners. As you can see in the next image, the project is conceived by institutions which have the infrastructure for developing solar cells. You can read a complete description in the following link (About Starcell-Project)

STARCELL organization structure for CZTS development of solar cells and scale-up to PV modules

Challenges of kesterite technology: Doping and alloying 

The main technological challenge of kesterites is their Low Voc.  For example, the sulfo-selenide kesterite or CZTSSe has a Voc of 513 mV [2] compared to commercial CIGSe solar cells which reach 734 mV [3].  Dr. Saucedo said that some bulk properties of the kesterite related to recombination process should be enhanced controlling the following techniques:

IFUAP - Physics Institute BUAP (POSDOC)

Last April 2019, I wrote a project for a postdoctoral stay at IFUAP. This stay will be founded by PRODEP-SEP. The goal is to reinforce the photovoltaic area developing thin-film solar cells based on novel materials. The application specifies a 3-month deadline for a response (late July). However,  when the deadline arrives, IFUAP said that this response can spend up to  5-months with no compromise. Therefore, this project can not be started.  

All of this is happening due to political reason. When the Mexican government changes most of the funds for public scientific research were frozen until politics trace the new route of investment. Somebodies say that it is due to a re-structure of the funds, but nobody can deny the collateral damage. There are a lot of unemployed people who were founded by Conacyt during their master or a Ph.D. degree.

No matter this situation, I embraced the risk and moved to Puebla City. Here I have been able to meet the researcher, its infrastructure, and the surroundings. BUAP is the Autonomous University of Puebla one of the best of this city.  After three weeks, I have been able to assist the weekly seminars (open to the public), interact with bachelors and Ph.D. Students.  When I saw for the first time the main IFUAP building, I could understand that the university is in a current expansion. They are building its Rectoria Tower.  I'll expect a positive response from IFUAP to be able to do science within collaboration with their specialist. 

Meanwhile, let's discover the history of Puebla located in their museums. And of course, prepare a short manual for solar cells design using SCAPS-1D software.

Fig 1: IFUAP  - Institute of physics - BUAP (Puebla) 

Fig 2: Profile measurements of thin films (co-work and training) 

Chemical deposition of antimony sulfide & silver antimony sulfide

The following photographs show the first 30 minutes of the solution reaction for chemical deposition of antimony sulfide thin films. This material is a p-type semiconductor. It is deposited as an amorphous source (Sb-S). The films have the necessary content to produce an orthorhombic lattice after heating above 250 ºC.

Application

Antimony sulfide is used for the research of thin-film solar cells with the following configuration TCO/CdS/Absorber/BackContact.  This film is achieved using the formula reported in the paper I publish during my Ph.D. program (With no AgNO3).  Find it here.

For tips about deposition, feel free to write a comment!

[1] J. Capistrán Martínez, P.K. Nair, Photoconductive thin films of AgSbS2 with cubic crystalline structure in solar cells, Physica Status Solidi (a). 212 (2015) 2869–2876. doi:10.1002/pssa.201532496.

Initial deposition condition temperature near 10 ºC

The reaction of the Sb-S solution begins after 10 minutes. 

The color of the reaction change completely at 30 minutes, this color will be maintained until the controlled precipitation finish. 

After 3-4 hours of deposition, the films look good, there is adherence to the glass substrate and specular reflection in the surface.