The solar cell is based on the titanium carbide MXene and is claimed to have retained around 99% of its initial efficiency for more than 600 days of ambient air storage. The device was built using spray coating to directly deposit the titanium carbide flakes on the cell’s rear side.

Scientists led by Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) have developed a heterojunction solar cell by replacing traditional silver metal contacts with rear electrodes based on two-dimensional transition metal carbides and nitrides known as MXenes.

Earth-abundant MXenes compounds take their name from their graphene-like morphology and are made via selective etching of certain atomic layers from a bulk crystal known as MAX.

The researchers employed an MXenes compound known as titanium carbide MXene (Ti3C2Tx), which has already been used in previous research for application in solar cells, to fabricate the films with a thickness of less than 2μm that were used as electrodes for the solar cell. “Taking advantage of their solution processability and hydrophilicity, we opted for spray coating to directly deposit the Ti3C2Tx flakes on the [rear] side of solar cells,” they further explained. “The automated spray-coating system allows for fine thickness control and homogeneity over large areas, bringing industrial relevance to the process.

The ultrasonic automated spraying system used by the Saudi group operates at moderate substrate temperatures of between 150 and 180
degrees Celsius, which is described as a critical threshold to avoid the degradation of solar cells. “Generally, spraying at higher temperatures may promote the effusion of hydrogen from the hydrogenated amorphous silicon (a-Si:H) passivation stacks, resulting in low open-circuit voltage values,” it highlighted.

An MXene-contacted heterojunction cell with an area of 4.2cm2 was able to achieve a power conversion efficiency of 20.1%, which compares to 21.6% in a similar device built with silver contacts. “Notably, the Ti3C2Tx-rear-contacted devices have retained around 99% of their initial efficiency for more than 600 days of ambient air storage,” the academics stated. “Their performance is comparable with state-of-the-art solar cells contacted with sputtered silver electrodes.”

They also fabricated a bigger solar cell, with an area of 243cm2, and found it showed low series resistance.

Their approach was introduced in the paper “Scaled Deposition of Ti3C2Tx MXene on Complex Surfaces: Application Assessment as Rear Electrodes for Silicon Heterojunction Solar Cells,” published in ACS Nano. “Our findings demonstrate the high-throughput potential of spray-coated MXene-based electrodes for solar cells, in addition to a wider variety of electronic device applications,” they concluded.

Scientists from Dongguk University, Korea University, and Hamad Bin Khalifa University (HBKU) have recently investigated how two-dimensional transition metal carbides and nitrides known as MXenes could be used as materials for solar cells. According to them, these materials exhibit good conductive behavior but a few of them with suitable surface terminations can also exhibit semiconductor-like behavior. In their work, they identified Ti3C2Tx as the most promising material.