Hysteresis-Free Planar Perovskite Solar Module with 19.1% Efficiency by Interfacial Defects Passivation

In few years, perovskite solar devices have reached high efficiency on lab scale cells. Upscaling to module size, effective perovskite recipe and posttreatment are of paramount importance to the breakthrough of the technology. Herein this work, the development of a low-temperature planar n-i-p perovskite module (11 cm(2) aperture area, 91% geometrical fill factor) is reported on, exploiting the defect passivation strategy to achieve an efficiency of 19.1% (2% losses stabilized) with near-zero hysteresis, that is the most unsolved issue in the perovskite photovoltaic technology. The I/Br (iodine/bromide) halide ion ratio of the triple-cation perovskite formulation and deposition procedure are optimized to move from small area to module device and to avoid the detrimental effect of dimethyl sulfoxide (DMSO) solvent. The organic halide salt phenethylammonium iodide (PEAI) is adopted as surface passivation material on module size to suppress perovskite defects. Finally, homogeneous and defect-free layers from cell to module with only 8% relative efficiency losses, high reproducibility, and optimized interconnections are scaled by laser ablation methods. The homogeneity of the perovskite layers and of the full stack was assessed by optical, morphological, and light beam-induced current (LBIC) mapping characterizations.

Highly efficient, stable and hysteresis-less planar perovskite solar cell based on chemical bath treated Zn2SnO4 electron transport layer

Seckin Akin, Michael Graetzel, Ulf Anders Hagfeldt, Marco Alejandro Ruiz Preciado, Faranak Sadegh, Mohammad Mahdi Tavakoli, Wolfgang Richard Tress, Zaiwei Wang

The electron transport layer (ETL) is a key constituent in perovskite solar cells (PSCs). It should provide efficient and selective electron extraction, low resistivity and high stability. Here, zinc stannate (Zn2SnO4, ZSO) is employed as an ETL in planar PSCs. A surface treatment of a compact ZSO layer is introduced based on chemical bath deposition (CBD). CBD results in a dense and uniform surface morphology that promotes the formation of a perovskite film with better surface coverage and enlarged grains, which lead to reduced recombination losses. Such improvements effectively increase the charge extraction at ETL/perovskite interface and reduce trapassisted recombination, which results in a remarkable photovoltaic performance, low hysteresis index, and good reproducibility. The efficiency of PSCs based on CBD-modified ZSO ETL has been dramatically increased from 19.3% to 21.3% with a notable increase in open circuit voltage of 60 mV compared to bare ZSO-based devices. This value is among the highest for ZSO-based PSCs. More importantly, the CBD-treated PSCs exhibited good stability, retaining more than 90% of its initial efficiency over 1000 h under continuous illumination at maximum power point. These results demonstrate that CBD can significantly improve the performance and stability of ZSO-based planar PSCs, a crucial requirement for commercialization.

ELSEVIER2020

Role of ions and interfaces for efficient and stable perovskite solar cells

Anand Agarwalla

Perovskite Solar Cells (PSCs) have grabbed global attention of the researchers due to their outstanding Photovoltaic (PV) performance. PSCs have the potential to be the future of the PV technology as they can generate power with performance being comparable with the leading Silicon solar cells, with the cost being lower than Silicon solar cells. The enormous potential of PSCs is evident from the fact that the efficiency of these cells has risen from 3.8% to 25.5% within a decade, and it is continuously rising to date. In my thesis, I investigate the impact of ions in the bulk of perovskite and also look at the ETL-perovskite interface to create a simpler, more efficient, more reproducible and more stable system for PSCs. At first, I managed to achieve high efficiency devices with the standard triple cation perovskite on both planar and mesoporous n-i-p ETL device architecture. Adding KI to the already established compositions showed a boost in performance of the solar cells while significantly reducing hysteresis. We then performed a systematic study of KI on various perovskite compositions comprised of FA, MA, Cs, Rb, I and Br ions. We demonstrated that KI reacts with the bromide ions in perovskite passivating the grains leading to a red shift hence and improvement in current density as well as efficiency.MAPbBr3 is generally used is small proportions along with FAPbI3 to stabilise the phase of FAPbI3. But the effect of Br- ions on the perovskite performance was relatively unknown. The introduction of Br- ions in the lattice causes a blue shift in the band gap pushing it further away from the ideal Shockley-Quessier limit. On top of this, the effect of MAPbBr3 on phase stability of FAPbI3 is similar to the effect of CsPbI3. This led me to examine the impact of reduced bromine concentration of the device performance. Interestingly, reducing the bromine concentration not only leads to a red shift in band gap, hence increasing the current density but also causes a reduced voltage loss resulting in much superior performance. Moreover, the Br- ions cause increased halide diffusion in the bulk leading to decreased stability with higher the bromide concentration.While perovskite composition plays an important role in defining the device characteristics, it could be argued that the interfaces play an equally important role in doing the same. With the rise in usage of SnO2 as viable substitute for TiO2 as ETL, I explore the effect of using TiO2 particles that exhibit similar properties to the SnO2 particles. These smaller size TiO2 nanoparticles can form a very thin, compact, uniform and pin-hole free layer with a morphology that follows the morphology of FTO. This results in a reduced recombination in the interface of TiO2 and perovskite causing the open circuit voltage and hence the device performance to improve significantly.

EPFL2021

Efficient Monolithic Perovskite/Silicon Tandem Solar Cell with Cell Area >1 cm

Christophe Ballif, Stefaan De Wolf, Luc Fesquet, Björn Niesen, Johannes Peter Seif, Arnaud Walter, Ching-Hsun Weng, Jérémie Werner

Monolithic perovskite/crystalline silicon tandem solar cells hold great promise for further performance improvement of well-established silicon photovoltaics; however, monolithic tandem integration is challenging, evidenced by the modest performances and small-area devices reported so far. Here we present first a low-temperature process for semitransparent perovskite solar cells, yielding efficiencies of up to 14.5%. Then, we implement this process to fabricate monolithic perovskite/silicon heterojunction tandem solar cells yielding efficiencies of up to 21.2 and 19.2% for cell areas of 0.17 and 1.22 cm2, respectively. Both efficiencies are well above those of the involved subcells. These single-junction perovskite and tandem solar cells are hysteresis-free and demonstrate steady performance under maximum power point tracking for several minutes. Finally, we present the effects of varying the intermediate recombination layer and hole transport layer thicknesses on tandem cell photocurrent generation, experimentally and by transfer matrix simulations.

Amer Chemical Soc2016

Role of ions and interfaces for efficient and stable perovskite solar cells

Anand Agarwalla

EPFL2021