Photovoltaic innovation boosts the efficiency of green energy
Generating electricity with almost no CO2 equivalent emissions, photovoltaic (PV) technology offers an attractive green energy solution. Yet, there is currently very little European solar cell or module production, necessitating imports with their carbon footprints and supply risks. “It has become increasingly difficult to compete with Asian countries, mainly China, to manufacture PV technology. The real barrier to rolling out PV solutions is, however, mostly not technological, but political priorities,” says Uli Würfel, coordinator of the EU-funded DIAMOND(opens in new window) project. DIAMOND’s printable PV architectures – scalable for production – help boost the maturity of European solutions.
Perovskite PV design and material innovations
Most solar panels are made from silicon, thanks to its abundance and reliability, but perovskites offer easier fabrication and potentially lower costs. Perovskites(opens in new window) for PVs are a class of synthetic crystalline materials made from a range of sources including lead, tin, bromine and chlorine. To increase the durability and efficiency of perovskite solar cells, DIAMOND first identified the best combination of materials for key PV components. The researchers developed perovskite PV devices with conventional metal back electrodes, alongside carbon-based ones. They also investigated the use of lead-tin based absorbers to reduce lead content. Three key innovations were combined to give DIAMOND’s solution more stability than previous PV solar cells. Firstly, a carbon-based back electrode (electrical contacts collecting and transporting photogenerated charge to external circuits), was developed. “These versions improve long-term stability compared to conventional metal electrodes,” adds Würfel from the Fraunhofer Society(opens in new window), the project host. Mitigating the use of toxic lead, sequestration layers were developed from a novel metal organic framework which, rich in chelating groups, immobilise lead ions. Lastly, an innovative design sealed the solar unit. This so-called ‘hermetic encapsulation’ is tricky because the glues typically used to bond the glass solar panels which sandwich the temperature-sensitive materials, increase risks of contamination and heat damage. “We substituted glue with a printed layer of glass frit materials, melted to bond them to the glass plates, offering environmental protection for over 25 years,” explains Würfel.
Enhanced power conversion efficiency
Testing to compare DIAMOND’s power conversion efficiency (PCE) – how much sunlight is converted into electrical power – with silicon PV, returned encouraging results. The perovskite solar cell with a lead/tin mixed absorber returned a PCE of 25.86 %; while the perovskite solar cell with carbon-based back electrode achieved a PCE of 21.5 % (22.9 % shortly after project completion). With mini solar cell modules (panels), a PCE of 23.28 % was reached on an area of 29 cm2. While a larger module of over 100 cm2 with a carbon-based back electrode processed in air (as opposed to using more expensive inert atmospheres such as nitrogen), realised a PCE of over 18 %. “We were also delighted to record a solar cell PCE rate of just above 27 %, actually beating the world record for crystalline silicon solar cells at the time of proposal submission,” notes Würfel.
Sustainable by design
The team pursued device designs, components and processes with the lowest CO2 footprints and the highest recycle potential. For example, when fabricating modules, each layer was analysed for potential environmental impact, with a fully recyclable module created as a proof of concept. “Our results reinforce the potential of perovskite PV technology, which when transferred to industry, will create new jobs and reduce dependency on imports of PV panels and ultimately energy itself,” concludes Würfel. Towards this end, the team are now scaling up the size of their PV modules, while continuing to enhance PCEs and operational lifetimes.