By Dr Samrana Kazim, BCMaterials-Basque Center for Materials, Applications and Nanostructures, Leioa, Spain.
Hybrid organic-inorganic perovskite solar cells (PSCs) have shown a substantial progress in power conversion efficiencies due to their astounding optoelectronic properties and low cost synthesis, making them one of the best alternative PV material among the third generation photovoltaics(PV). Presently, a certified PCE of 23.3 % has reached , demonstrating a dramatically rapid increase from their first reported PCE of 3.8% in 2009, and an exceptional rise among the PV technology. Among, the various device architectures adopted for the PSCs, to date, mesoscopic nanostructure and planar structure were promising to produce efficient PSCs.  In both architectures, perovskite is sandwiched between the n-type electron transporting layer(ETL) and p-type hole transporting layer (HTL). However, in mesoscopic nanostructure, the presence of mesoporous scaffold increases the stability of PSCs due to infiltration process avoiding direct contact to the harsh atmospheric condition.
The hole transporting layer (HTL) plays an important role to fabricate efficient devices. Presently, among the organic hole transport materials (HTMs), Spiro-OMeTAD and its derivatives signifies the state of the art HTMs.  However, their multistep synthetic route and complex purification, obstructs progress toward commercialization of perovskite PV technology. Furthermore, these HTMs needs additional chemical doping to increases the conductivity and shift of fermi level towards the HOMO of HTM, in order to efficient hole transport and extraction through the top metal electrode. However, the usage of these hygroscopic p-type dopants and additives (Li-TFSI and t-BP) accelerates the degradation of PSC performance. Thus, to achieve stable and efficient PSCs, it is really crucial to develop dopant free HTMs or find the suitable hydrophobic dopant to avoid degradation of moisture sensitive perovskite layer.
In this talk, I will focus on two different strategies for hole transporting layer to prepare stable and efficient devices. I will summarize some of our results [4-6] on small molecule based dopant free HTMs, and will also introduce recently developed ubiquitous, hydrophobic p-type dopant for hole transport material such as Spiro-OMeTAD, which improves not only the cell performance but also the long term stability.  Additionally, this hydrophobic doping route can be employed to a wide range of organic semiconductors to increase the conductivity of HTM and control the degradation of the moisture-sensitive perovskite layer. The impressive results pave the way to the use of this effective dopant for HTMs which can effectively enhance the lifetime of PSCs devices.
 L. Calió, S. Kazim, et.al. Angew. Chemie – Int. Ed. 55 (2016) 14522–14545.
 D. Bi, et al. Sci. Adv. 2 (2016) e1501170.
 S.Kazim et.al. Energy Environ. Sci. 8 (2015) 2015, 1816-1823
 F.J. Ramos et.al. RSC Adv. 5 (2015) 53426–53432.
 L. Calió, et.al. Sol. Energy Mater. Sol. Cells. 163 (2017) 237–241.
 L. Caliò, et.al. Joule. (2018) 1–16.
Dr. Samrana Kazim obtained her Master degree (M.Sc) and doctoral degree(Ph.D.) in Materials chemistry at JMI university, New Delhi (India). After finishing her Ph.D. in 2008, she moved to Institute of Macromolecular Chemistry (IMC), Prague on IUPAC/UNESCO fellowship. Later, she became a staff scientist in IMC before moving to corporate research. Before joining BCMaterials as Senior scientist, she worked as a permanent senior scientist at Abengoa Research, a corporate research centre of Abengoa from 2013-2017. She has published >40 research articles in reputed journals in the field of material science, energy and nanotechnology, co-authored 2 book chapters and inventor of numerous patents in the field of energy conversion and storage. Her field of research interest includes Electro-optical characterization of organic semiconductors, perovskite solar cells, hybrid inorganic-organic nanocomposites and plasmonics.