Reduction in the Interfacial Trap Density of Mechanochemically Synthesized MAPbI(3)

Organo-lead halide perovskites have emerged as promising light harvesting materials for solar cells. The ability to prepare high quality films with a low concentration of defects is essential for obtaining high device performance. Here, we advance the procedure for the fabrication of efficient perovskite solar cells (PSCs) based on mechanochemically synthesized MAPbI3. The use of mechano-perovskite for the thin film formation provides a high degree of control of the stoichiometry and allows for the growth of relatively large crystalline grains. The best device achieved a maximum PCE of 17.5% from a current-voltage scan (J-V), which stabilized at 16.8% after 60 s of maximum power point tracking. Strikingly, PSCs based on MAPbI(3) mechanoperovskite exhibit lower "hysteretic" behavior in comparison to that comprising MAPbI(3) obtained from the conventional solvothermal reaction between PbI2 and MAI. To gain a better understanding of the difference in J V hysteresis, we analyze the charge/ion accumulation mechanism and identify the defect energy distribution in the resulting MAPbI(3) based, devices. These results indicate that the use of mechanochemically synthesized perovskites provides a promising strategy for the formation of crystalline films demonstrating slow charge recombination and low trap density.

A chain is as strong as its weakest link - Stability study of MAPbI(3) under light and temperature

Michael Graetzel, Ulf Anders Hagfeldt, Philippe Jürgen Holzhey, Michael Saliba, Silver Hamill Turren Cruz, Amita Ummadisingu, Pankaj Kumar Yadav

The stability of perovskite solar cells is a key issue for industrial development. One reason for this is the volatile organic methylammonium (MA) cation, which is prone to degas under elevated temperatures from the perovskite. At the same time, small amounts of MA are used for practically all highest performing solar cells. These compositions have also shown relatively promising stabilities. This raises the question of MA stability with respect to different, application-dependent stability requirements. Interestingly, MA stability was mainly studied on thin films that differ from full devices or with architectures which are also prone to degrade. Therefore, the degradation behavior on complete MA containing devices with a relatively stable architecture is required to quantify the long-term stability of MA. This enables to determine at which timescales MA is unstable and which role it can play in future compositions. If MA is indeed unstable at much longer timescales than previously recorded, it also indicates that more severe degradation pathways are currently underappreciated. Here, "weakest link" MAPbI(3) solar cells show stability where devices retained 100% of their initial efficiency over 1000 h of aging under constant illumination and maximum power point tracking at 20 degrees C. At elevated temperatures of 50 and 65 degrees C, the devices retained 100% and 90% of their initial efficiency after 500 h of illumination, respectively. Impressively, at 95 degrees C the MAPbI(3) device retained 85% of its initial efficiency after 500 h under constant illumination, which is some of the best stability data reported to date for MA. Thus, MA-containing devices require further studying. Nevertheless to achieve the necessary industrial lifetimes of more than 25 years, the complete removal of MA is a sensible precaution to systematically avoid any long-term risk factors.

2019

Formation of High-Performance Multi-Cation Halide Perovskites Photovoltaics by delta-CsPbI3/delta-RbPbI3 Seed-Assisted Heterogeneous Nucleation

Essa Awadh R Alharbi, Masaud Hassan S Almalki, Thomas Paul Baumeler, Felix Thomas Eickemeyer, Ulf Anders Hagfeldt, Anurag Krishna, Mounir Driss Mensi, Olivier Ouellette, Linfeng Pan, Zaiwei Wang, Bowen Yang, Shaik Mohammed Zakeeruddin

The performance of perovskite solar cells is highly dependent on the fabrication method; thus, controlling the growth mechanism of perovskite crystals is a promising way towards increasing their efficiency and stability. Herein, a multi-cation halide composition of perovskite solar cells is engineered via the two-step sequential deposition method. Strikingly, it is found that adding mixtures of 1D polymorphs of orthorhombic delta-RbPbI3 and delta-CsPbI3 to the PbI2 precursor solution induces the formation of porous mesostructured hexagonal films. This porosity greatly facilitates the heterogeneous nucleation and the penetration of FA (formamidinium)/MA (methylammonium) cations within the PbI2 film. Thus, the subsequent conversion of PbI2 into the desired multication cubic alpha-structure by exposing it to a solution of formamidinium methylammonium halides is greatly enhanced. During the conversion step, the delta-CsPbI3 also is fully integrated into the 3D mixed cation perovskite lattice, which exhibits high crystallinity and superior optoelectronic properties. The champion device shows a power conversion efficiency (PCE) over 22%. Furthermore, these devices exhibit enhanced operational stability, with the best device retaining more than 90% of its initial value of PCE under 1 Sun illumination with maximum power point tracking for 400 h.

WILEY-V C H VERLAG GMBH2021

Phosphine Oxide Derivative as a Passivating Agent to Enhance the Performance of Perovskite Solar Cells

Aron Joel Huckaba, Cansu Igci, Hiroyuki Kanda, Hobeom Kim, Mounir Driss Mensi, Mohammad Khaja Nazeeruddin, Valentin Ianis Emmanuel Queloz, Albertus Adrian Sutanto

Defects of metal-halide perovskites detrimentally influence the optoelectronic properties of the thin film and, ultimately, the photovoltaic performance of perovskite solar cells (PSCs). Especially, defect-mediated nonradiative recombination that occurs at the perovskite interface significantly limits the power conversion efficiency (PCE) of PSCs. In this regard, interfacial engineering or surface treatment of perovskites has become a viable strategy for reducing the density of surface defects, thereby improving the PCE of PSCs. Here, an organic molecule, tris(5-((tetrahydro-2H-pyran-2-yl)oxy)pentyl) phosphine oxide (THPPO), is synthesized and introduced as a defect passivation agent in PSCs. The P.O terminal group of THPPO, a Lewis base, can passivate perovskite surface defects such as undercoordinated Pb2+. Consequently, improvement of PCEs from 19.87 to 20.70% and from 5.84 to 13.31% are achieved in n-i-p PSCs and hole-transporting layer (HTL)-free PSCs, respectively.

2021

A chain is as strong as its weakest link - Stability study of MAPbI(3) under light and temperature

Michael Graetzel, Ulf Anders Hagfeldt, Philippe Jürgen Holzhey, Michael Saliba, Silver Hamill Turren Cruz, Amita Ummadisingu, Pankaj Kumar Yadav

2019