Using Ag nanoparticles in the electron transport layer of perovskite solar cells to improve efficiency

The incorporation of metal nanoparticles within various types of photovoltaic technologies has been shown to increase the performance of organic solar cells, dye sensitized solar cells, and more recently perovskite solar cells. Using this type of nanostructured composite transport layer could help improve the efficiency and stability of perovskite solar cells whilst avoiding the use of dopants that can damage the perovskite layer. In this work, Ag nanoparticles are synthesized and used to form a SnO2:Ag nanoparticle composite transport layer for the first time. On its own, SnO2 is in one of the most efficient transport layers for perovskite solar cells. Upon inclusion of the Ag nanoparticles the recombination rate is increased (detrimental for device performance) as shown by impedance spectroscopy, and the charge carrier transfer and extraction is enhanced (beneficial for device performance) as shown by photoluminescence measurements. In order to balance these opposing factors, the nanoparticle concentration was optimized at an intermediate concentration with a corresponding power conversion efficiency increase from 13.4 +/- 0.7 % for reference solar cells without nanoparticles to 14.3 +/- 0.3 % for those with nanoparticles. These devices are one of the first examples of, and exhibit the highest reported efficiency for, perovskite solar cells fabricated completely in air with nanocomposite oxide layers. The protocol developed and reported here to improve the nanocomposite transport layer has general applicability in other fields, including LEDs, FETs, and electronic devices where transparency and conductivity are also required.