Lab tests: chromium lets cheap electrodes match gold in perovskite cells

A gold back electrode can cost around 60 euros per square meter of perovskite solar panel when it is only 100 nanometers thick. That is roughly three times the cost of an entire silicon panel, electronics included, according to the team behind a study published in Advanced Energy Materials. Their proposed substitute is a 5-nanometer layer of chromium placed between the perovskite and a cheap metal such as aluminum.

The problem is chemical. As a perovskite cell ages, halide ions escape from the active material and readily attack most metals. Gold largely resists that corrosion. The researchers’ analysis using X-ray photoelectron spectroscopy found that chromium forms a mixed metallic and oxidized barrier at the interface: it absorbs the chemical attack before the halides reach the aluminum underneath. The same protective effect appeared with copper and silver, suggesting the approach is not limited to one cheap metal.

In accelerated aging tests, aluminum alone degraded rapidly. With chromium added, it moved from the least stable option tested to one of the most stable, closely matching gold while using raw materials costing roughly one-hundred-thousandth as much. The cells were tested under combined heat and light at 0.76 suns and roughly 75°C, conditions designed to stress the devices rather than simulate ordinary operation directly.

The study found a second weak point in the transparent front electrode. ITO, or indium tin oxide, is widely used because light can pass through it, but depth-resolved mass spectrometry showed indium migrating into the perovskite. The metal appeared to create defects that accelerated light- and heat-induced breakdown. FTO — fluorine-doped tin oxide — contains no indium, and cells built with it avoided the performance loss that caused ITO-based devices to fail within a few hundred hours under the same stress.

And concretely? A perovskite cell could potentially replace two costly or unstable material choices at once: gold at the back and ITO at the front. In the team’s tests, cells using FTO and the chromium-aluminum bilayer tracked gold-based references for more than 1,000 hours of heat and simulated sunlight. That is a useful engineering direction for cheaper, more durable devices, but it remains a laboratory result rather than a demonstrated commercial panel.