Solar cells convert the ubiquitous power of the sun into electricity, making them an especially attractive source of sustainable energy. To do so, however, the cells should maintain their performance despite of a constant onslaught of the elements—humidity being a particular challenge for perovskite solar cells.
Sagar Jain at SPECIFIC is actively working on perovskite solar cells structure-property-performance relation, stability and toxicity problems of these devices. He told us that perovskite solar cells show competent certified efficiency of more than 22% [1,2] which is close match to the commercially available silicon solar cells. Although this is all impressive, the record perovskite solar cells still employ highly expensive traditional Spiro-OMeTAD based hole transport material (costs – 280 £/gram)  additionally this requires doping of hygroscopic salts (known as LiTFSI) to improve the device performance. This makes the devices susceptible for the degradation, particularly when the ambient is humid.
In the paper in Advanced Energy Materials, Dr. Sagar M. Jain from Swansea University Bay Campus, Prof. Prashant Sonar from Queensland University of Technology, and their co-workers report derivatives of the dye anthanthrone (ANT) as moisture-resistant, dopant-free hole-transport materials (HTMs) for perovskite solar cells. The research work further explores the reason for why and how the new hole transport layer improves the perovskite device stability through employing detail investigation using several characterization techniques.
As a part of this international collaboration the novel hole-transport material is synthesized at Queensland University of Technology, Brisbane, Australia while the perovskite solar cells are prepared at SPECIFIC, Swansea University, Swansea UK.
Prof. Prashant Sonar from Queensland University of Technology, Brisbane told us more about the hole transport material that they prepared; “The Anthanthrone (in short ANT) or also called as VAT orange 3 dye (from its color) is a promising rarely used low cost starting polycyclic aromatic hydrocarbon conjugated building block. Its 4, 10, 6 and 12 positions can be utilized effectively for chemical functionalization and which can create a range of exciting new conjugated materials with interesting optoelectronic properties.”
Researchers from Queensland University of technology designed and synthesized two novel hole-transporting materials namely ACE-ANT-ACE and TPA-ANT-TPA for Perovskite solar cell devices from ANT dye. While, Sagar prepared high efficiency dopant-free-HTM-based devices and compared them to devices based on doped Spiro-OMeTAD hole transport layer.
The decrease in photovoltaic performance caused by prolonged exposure to humidity is much slower for TPA-ANT-TPA-based devices than for those using Spiro-OMeTAD. Improved quenching of perovskite photoluminescence and more effective hole extraction are also evidenced in TPA-ANT-TPA over Spiro-OMeTAD.
On final remark Sagar told us that; “Although dopant salt improves the efficiency of solar cells. For improvement of perovskite solar cell stability, it is very important to avoid their use due to their hygroscopic nature. Our new hole transport material not only offers better performance and stability (by avoiding use of hygroscopic dopants) to perovskite solar cells but also minimizes the cost by the use of inexpensive new hole transport material as an efficient alternative to expensive Spiro-OmeTAD (which is expensive than gold) for solar cells.”
This important finding and will be a breakthrough in perovskite solar cell stability and will attract researcher across world to make solar cells free from hygroscopic dopants.
The patent titled “Novel semiconductor hole transport materials for perovskite solar cells” has been filled for the family of these new holes transport materials and the devices received certification from Newport corporation, California, USA.
To learn more about this inexpensive, highly stable, dopant-free HTM for perovskite solar cells, please visit the Advanced Energy Materials paper here or watch our video below.