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)

Abstract

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.

Highlights

• 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 

Notes: 

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

Fabrication of Titanium dioxide as a compact layer for Perovskite and thin-film solar cells

Special thanks for Dra Hailin Zao Hu at IER-UNAM who let me collaborate and learn from their group the methodology for TiO2 compact layer deposition.  All the training was possible with the assistance of Ph.D. student Fabian and undergraduate  Ing. Gabriela Abrego from UTEZ.

Preparing TCO with magic tape  for HRT layer deposition 

Spin coater  and micropipette are the essential tools for TiO2 deposition 

First heating of the compact layer over a hot plate : low temperature

Second and final heating - Sintering TiO2 on a muffle furnace : high temperature

Compact TiO2 layer deposited over a TCO for thin-film chalcogenide or Perovskite solar cells. 

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: