The future is lead-free for perovskite solar cells

Example of a tin halide perovskite solar cell

A lead-free and non-toxic alternative to current perovskite solar-cell technology has been reported by researchers in the UK: tin halide perovskite solar cells. They are also cheaper to manufacture than the silicon solar cells currently dominating the market.

Nakita Noel, part of Henry Snaith’s research team at the University of Oxford, describes how perovskite materials have caused a bit of a whirlwind since they came out in 2009: ‘Everybody that’s working in the solar community is looking to beat silicon.’ Despite the high efficiency of conventional crystalline silicon solar cells (around 20%), high production and installation costs decrease their economic feasibility and widespread use.

The challenge to find a cheaper alternative led to the development of perovskite-based solar cells, as organic–inorganic metal trihalide perovskites have both abundant and cheap starting materials. However, the presence of lead in some semiconductors could create toxicology issues in the future. As Noel puts it ‘every conference you present at somebody is bound to put up their hand and ask “What about the lead – isn’t this toxic?”’

‘The drive for us was looking for something to replace the lead that we can still get photovoltaic performance out of,’ she explains. They tested the lead-free perovskite, methylammonium tin triiodide (CH3NH3SnX3) as their photoactive material. Due to the instability of CH3NH3SnX3 when exposed to oxygen and moisture, all material and device processing was conducted in a nitrogen-filled glovebox. Equimolar quantities of SnI2 and CH3NH3I were dissolved in degassed N-dimethylformamide, with the solution then spin-coated onto a substrate.

Scanning Electron Microscope (SEM) image of a perovskite film spin-coated onto mesoporous titanium dioxide

This research demonstrates the first operation of an entirely lead-free perovskite solar cell, achieving 6% efficiency with the prototype. The team believe that if the material was stable the diffusion length, currently ~30nm, could increase closer to that of lead, ~1µm. This would enable more current to be accepted from the device, increasing efficiency.

Brian Hardin, co-founder of PLANT PV, US, and an expert in new materials for photovoltaic cells, says the study ‘should be considered a seminal work on alternative perovskites and is extremely valuable to the field as they look to better understand how changes in chemistry affect solar cell performance and stability.’

The team are now working to stabilise the tin material itself, and have already achieved promising results.


This paper is free to access until 27 June 2014. Download it here:

N K Noel et al, Energy Environ. Sci., 2014, DOI: 10.1039/c4ee01076k

Related Content

The power of perovskites

22 August 2014 Premium contentFeature

news image

Andy Extance finds out how the efficiency of perovskite solar cells has risen so quickly

Spray-deposition steers perovskite solar cells towards commercialisation

29 July 2014 Research

news image

Scientists make headway on scalability hurdles

Most Read

Antimicrobial resistance will kill 300 million by 2050 without action

16 December 2014 News and Analysis

news image

UK report says resistance will cost global economy $100 trillion

Cutting edge chemistry in 2014

10 December 2014 Research

news image

We take a look back at the year's most interesting chemical science stories

Most Commented

Smart skin for prosthetic limbs senses heat and touch

12 December 2014 Research

news image

Ultra-thin plastic skin can bend and flex without affecting the skin's ability to detect stimuli

Chemistry behind the ‘blue man’ unlocked

1 November 2012 Research

news image

Biochemical model suggests that silver ions, not nanoparticles, cause a rare skin complaint