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

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.

Phosphonic Acid Modification of the Electron Selective Contact: Interfacial Effects in Perovskite Solar Cells

Juan-Pablo Correa-Baena, Ulf Anders Hagfeldt, Rebecca Hill, Wolfgang Richard Tress, Silver Hamill Turren Cruz

The role electron-transport layers (ETLs) play in perovskite solar cells (PSCs) is still widely debated. Conduction band alignment at the perovskite/ETL interface has been suggested to be an important role for the performance of the solar cells. However, little is known about the effects of work-function shifts on the solar-cell performance, and specifically, the open-circuit voltage (V-OC). Here, the effects of surface modification of SnO2 ETLs using polar phosphonic acids are investigated, including the effects on work function, surface energy, device performance, and device stability in inert atmosphere. The phosphonic acid modifications did not have a large effect on V-OC; however, a sharp decrease in the overall device performance was found, mostly due to reduced fill factors. When exposed to conditions of low oxygen concentration, the phosphonic acid surface modified devices yielded current-voltage (J-V) curves with considerably lower hysteresis than those based on unmodified SnO2. This suggests that this modification method may be valuable for achieving stabilized power conversion efficiency without hysteresis.

AMER CHEMICAL SOC2019

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

Ulf Anders Hagfeldt, Jiajia Suo, Bowen Yang

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.

WILEY-V C H VERLAG GMBH2022

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