Improved Interfacial Crystallization by Synergic Effects of Precursor Solution Stoichiometry and Conjugated Polyelectrolyte Interlayer for High Open-Circuit Voltage of Perovskite Photovoltaic Diodes

Abstract

The open-circuit voltage (V oc) of perovskite photovoltaic diodes depends largely on the selection of charge transport layers (CTLs) and surface passivation, which makes it important to understand the physical processes occurring at the interface between the perovskite and a CTL. We provide a direct correlation between V oc and the interfacial characteristics of perovskites tuned through stoichiometry engineering of precursor solutions and surface modification of the underlying poly­(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) layer. Poor quality interfacial perovskite crystals were observed on top of the PEDOT:PSS layer, resulting in strong interfacial recombination and a low V oc. In contrast, the growth of the interfacial perovskite crystals was significantly improved by the synergic effects of varying the precursor solution composition and covering the surface with a pH-neutral conjugated polyelectrolyte, poly­[2,6-(4,4-bis­(potassium butanylsulfonate)-4H-cyclopenta­[2,1-b;3,4-b′]­dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (CPE-K), which possesses potassium ions as counter ions. The influence of the energy-level alignment at the interface on V oc was also discussed. Our findings highlight that improved perovskite crystallization at the interface can facilitate bulk growth of perovskite grains in the vertical direction and effectively suppress nonradiative surface charge recombination, thus enhancing the short-circuit current and V oc.

Conjugated Polyelectrolyte-Passivated Stable Perovskite Solar Cells for Efficiency Beyond 20%

“…The most effective technique to obtain defect-free, superior-quality films with good surface coverage is the incorporation of suitable passivation additives in the perovskite layer, which can reduce the trap states, minimize hysteresis, and enhance device stability. , Several small molecular additives, having numerous functional groups (such as −COOH, −NH 2 , −OH, −SH, and so forth), have been used for passivation that diminish the trap states and control the crystallization process of the perovskite as well. − Again, ionic molecules can also suppress the electronic defect states in the perovskite and considerably enhance device efficiency and stability. − Conjugated and nonconjugated polymers have also been used as passivating agents, which can enhance the device stability by significantly increasing the hydrophobicity of the perovskite layer. − Compared to small molecular additives, polymers have an advantage of preferential orientation along the GBs due to their bigger size. This results in crystalline, defect-free perovskite films with larger grain sizes, whereas the small molecules may be combined with the perovskite lattice. , Although conjugated polyelectrolytes (CPEs) are being vastly used as transport layers in PSCs, − their exploration as passivation additives in perovskite devices is rather not common.…”

Improving the Structure and Cycling Stability of Ni-Rich Layered Cathodes by Dual Modification of Yttrium Doping and Surface Coating

“…To ensure a stabilized solid–electrolyte interface and overall structural integrity, cation substitution and surface modification are extensively considered as potential methods to improve the electrochemical properties of cathode materials. Regarding surface modification, scores of coating layers including fluorides, phosphates, metal oxides, and fast ionic conductors were utilized to protect the cathode surface. ,− Specifically, yttrium orthophosphate (YPO 4 ) with excellent conductivity and good thermal stability showed great ability to facilitate ion transfer and decrease heat generation through repressing the electrolyte erosion. It is stated that yttrium orthophosphate (YPO 4 ) is geared to the space group of I 4 1 / amd with a tetragonal symmetry ( a = b = 6.822 Å), and the chains are parallel to the c -axis of the corner-sharing structural units constructed out of a tetrahedron (PO 4 ) and a dodecahedron (YO 8 ), which are joined together by an edge, safeguarding its superior structural stability .…”

The importance of sulfonate to the self-doping mechanism of the water-soluble conjugated polyelectrolyte PCPDTBT-SO3K

“…16 CPEs have been used in a wide variety of applications such as biosensors, as an interlayer or a conductive buffer layer in organic and perovskite photovoltaics, as an interconnective layer between top and bottom cells in tandem organic solar cells, as the active layer in light-emitting electrochemical cells, to modify the injection barrier in OFETs, and in organic thermoelectrics. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] CPEs have also been recently shown to act as p-or n-type dopants for carbon nanotubes, a property that is modulated by changing the charge of the ionic groups of the CPEs. 17 CPE/graphene hetero-bilayer 2D nanocomposites also exhibit a unique, temperature switchable type of electrical conductivity.…”