Recent Progress of Inverted Perovskite Solar Cells with a Modified PEDOT:PSS Hole Transport Layer

Organic-inorganic hybrid perovskite solar cells (PSCs) has achieved the power conversion efficiency (PCE) of 25.2% in the last 10 years, and the PCE of inverted PSCs has reached >22%. The rapid enhancement has partly benefited from the employment of suitable hole transport layers. Especially, poly(3,4-ethenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most widely used polymer hole transport materials in inverted PSCs, because of its high optical transparency in the visible region and low-temperature processing condition. However, the PCE and stability of PSCs based on pristine PEDOT:PSS are far from satisfactory, which are ascribed to low fitness between PEDOT:PSS and perovskite materials, in terms of work function, conductivity, film growth, and hydrophobicity. This paper summaries recent progress regarding to modifying/remedy the drawbacks of PEDOT:PSS to improve the PCE and stability. The systematically understanding of the mechanism of modified PEDOT:PSS and various characteristic methods are summarized here. This Review has the potential to guide the development of PSCs based on commercial PEDOT:PSS.

Improving the Performances of Perovskite Solar Cells via Modification of Electron Transport Layer

The commonly used electron transport material (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) for perovskite solar cells (PSC) with inverted planar structures suffers from properties such as poor film-forming. In this manuscript, we demonstrate a simple method to improve the film-forming properties of PCBM by doping PCBM with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) as the electron transport layer (ETL), which effectively enhances the performance of CH₃NH₃PbI₃ based solar cells. With 5 wt % F8BT in PCBM, the short circuit current (JSC) and fill factor (FF) of PSC both significantly increased from 17.21 ± 0.15 mA·cm-2 and 71.1 ± 0.07% to 19.28 ± 0.22 mA·cm-2 and 74.7 ± 0.21%, respectively, which led to a power conversion efficiency (PCE) improvement from 12.6 ± 0.24% to 15 ± 0.26%. The morphology investigation suggested that doping with F8BT facilitated the formation of a smooth and uniform ETL, which was favorable for the separation of electron-hole pairs, and therefore, an improved performance of PSC.

Oxygen- and Water-Induced Energetics Degradation in Organometal Halide Perovskites

Organometal halide perovskites are under rapid development, and significant focus has been placed on their stability that currently presents a major obstacle for practical application. Energetics plays a vital role in charge injection/extraction and transport properties in devices. Here, we in situ investigate oxygen- and water-induced energetics degradation in organometal halide perovskite films. Oxygen gas induces an upward shift of the vacuum level of the perovskite films because of the formation of an oxygen-induced surface dipole, water vapor causes a significant vacuum-level downshift, and the valence band binding energy referenced to the Fermi level simultaneously increases so as to keep the ionization potential of the perovskite films unchanged. Moreover, the chemical compositions, crystalline structures, surface morphologies, and dynamical properties also are monitored and analyzed in detail. These results are indispensable to understand the degradation mechanisms and to perform the optimizations of stable materials and devices in the future.