In a collaborative experiment to increase the power conversion efficiency of perovskite solar cells, a group of scientists introduced an electron transport layer made of indium sulfide to reduce the defect density and improve performance.

Experts from research universities in the United States, India, Iraq, Malaysia, Bangladesh, and Saudi Arabia simulated the indium-sulfide-based heterojunction organometallic perovskite solar cells (OPSC) with a newly developed model named— Solar Cell Capacitance Simulator-1D (SCAPS-1D).

The study titled “Insights into the photovoltaic properties of indium sulfide as an electron transport material in perovskite solar cells” was published in the Scientific Reports journal.

SCAPS-1D is an open-source program developed by the University of Gent in Belgium which helped scientists in the modeling up to seven components of the planar and graded photovoltaic structures, which include the current and voltage, quantum efficiency, recombination, and generation currents that impact the behavior of perovskite solar cells.

The scientists studied the continuity laws for electrons and holes using SCAPS-1D and found indium sulfide to be a potential alternate electron-transport material in OPSCs.

The introduction of indium sulfide increased the PV stability while boosting the overall efficiency of the perovskite cell. The teams also discovered that OPSCs performed well under 20-30 degrees Celsius after introducing indium sulfide as an electron transport layer.

Indium sulfide acts as the harvester material for OPSCs that generates charge carriers when exposed to sunlight. These carriers are delivered to electrodes by electron and hole transport materials.

The teams highlight that charging transporting materials is crucial to the entire photovoltaic performance of OPSCs. For instance, fabricating large devices using titanium oxide as the electron transport material is challenging as it requires operating temperatures of over 400 degrees Celsius.

Indium sulfide is an n-type semiconductor with excellent carrier mobility, nontoxicity, adequate bandgap, adjustable electrical properties, and good thermal durability, all of which are ideal for utilization as an electron transport layer in solar cells.

The scientists simulated a typical n-i-p PV architecture with 2-dimensional organic-inorganic perovskite nanocrystals as the photoactive film. The front and back electrodes comprised a compact indium-sulfide as electron transport material, and organic film made of Spiro-OMeTAD was included as the hole transport layer, followed by fluorine-containing facet-controlled stannic oxide and gold.

The alterations in the front and back electrodes helped the researchers determine the optimum thickness of the perovskite solar cell, which they said must be maintained at 0.7 µm for the highest performance of MAPbI3 (methylammonium lead iodide)-based single-cation OPSC.

They further observed that the increase in perovskite cell thickness supported by the use of indium sulfide as the electron transport material increased the efficiency of their perovskite solar cell to 20.15%.

The device with perovskite solar cells attained an open circuit voltage of 1.089 volts, a short-circuit voltage of 24.18 mA/cm2, and a fill factor of 76.4%.

In a similar research, scientists from King Abdullah University of Science and Technology combined perovskite top cells on industrially compatible, two-sided, textured silicon bottom cells and developed a perovskite-silicon tandem solar cell with a conversion efficiency of 33.2%.

Experts from North Carolina State University said in an experiment that channeling ions into defined pathways in perovskite materials improves perovskite solar cells’ stability and operational performance.