Employing surfactant-assisted hydrothermal synthesis to control CuGaO2 nanoparticle formation and improved carrier selectivity of perovskite solar cells

Delafossites like CuGaO2 have appeared as promising p-type semiconductor materials for opto-electronic applications mainly due to their high optical transparency and electrical conductivity. However, existing synthetic efforts usually result in particles with large diameter limiting their performance relevant to functional electronic applications. In this article, we report a novel surfactant-assisted hydrothermal synthesis method, which allows the development of ultrafine (~5 nm) monodispersed p-type CuGaO2 nanoparticles (NPs). We show that DMSO can be used as a ligand and dispersing solvent for stabilizing the CuGaO2 NPs. The resulting dispersion is used for the fabrication of dense, compact functional CuGaO2 electronic layer with properties relevant to advanced optoelectronic applications. As a proof of concept, the surfactant-assisted hydrothermal synthesized CuGaO2 is incorporated as a hole transporting layer (HTL) in the inverted p-i-n perovskite solar cell device architecture providing improved hole carrier selectivity and power conversion efficiency compared to conventional PEDOT:PSS HTL based perovskite solar cells

Room Temperature Nanoparticulate Interfacial Layers for Perovskite Solar Cells via solvothermal synthesis

We present a solvothermal synthetic route to produce monodispersed CuO nanoparticles (NPs) in the range of 5-10 nm that can be used as hole selective interfacial layer between indium tin oxide (ITO) and perovskite active layer for p-i-n perovskite solar cells by a spin casting the dispersions at room temperature. The bottom electrode interface modification provided by spherical CuO-NPs at room temperature promotes the formation of high quality perovskite photoactive layers with large crystal size and strong optical absorption. Furthermore, it is shown that the nanoparticulate nature of the CuO hole transporting interfacial layer can be used to improve light manipulation within perovskite solar cell device structure. The corresponding p-i-n CH3NH3PbI3-based solar cells show high Voc values of 1.09 V, which is significantly higher compared to the Voc values obtained with conventional PEDOT:PSS hole selective contact based perovskite solar cells

The Effect of Hole Transporting Layer in Charge Accumulation Properties of p-i-n Perovskite Solar Cells

The charge accumulation properties of p-i-n perovskite solar cells were investigated using three representative organic and inorganic hole transporting layer (HTLs): a) Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS, Al 4083), b) copper-doped nickel oxide (Cu:NiOx) and c) Copper oxide (CuO). Through impedance spectroscopy analysis and modelling it is shown that charge accumulation is decreased in the HTL/Perovskite interface, between PEDOT:PSS to Cu:NiOx and CuO respectively. This was indicative from the decrease in double layer capacitance (Cdl) and interfacial charge accumulation capacitance (Cel), resulting in an increase to recombination resistance (Rrec), thus decreased charge recombination events between the three HTLs. Through AFM measurements it is also shown that the reduced recombination events (followed by the increase in Rrec) is also a result of increased grain size between the three HTLs, thus reduction in the grain boundaries area. These charge accumulation properties of the three HTLs have resulted in an increase to the power conversion efficiency between the PEDOT:PSS (8.44%), Cu:NiOx (11.45%) and CuO (15.3%)-based devices

Long Thermal Stability of Inverted Perovskite Photovoltaics Incorporating Fullerene-based Diffusion Blocking Layer

In this article, the stability of p-i-n perovskite solar cells is studied under accelerated heat lifetime conditions (60 oC ,85oC and N2 atmosphere). By using a combination of buffer layer engineering, impedance spectroscopy and other characterization techniques, we propose the interaction of the perovskite active layer with the top Al metal electrode through diffusion mechanisms as the major thermal degradation pathway for planar inverted perovskite photovoltaics (PVs) under 85oC heat conditions. We show that by using thick solution processed fullerene buffer layer the perovskite active layer can be isolated from the top metal electrode and improve the lifetime performance of the inverted perovskite photovoltaics at 85 oC. Finally, we present an optimized solution processed inverted perovskite PV device using thick fullerene-based diffusion blocking layer with over 1000 hours accelerated heat lifetime performance at 60oC

High Performance Inverted Organic Photovoltaics Without Hole Selective Contact

A detailed investigation of the functionality of inverted organic photovoltaics (OPVs) using bare Ag contacts as top electrode is presented. The inverted OPVs without hole transporting layer (HTL) exhibit a significant gain in hole carrier selectivity and power conversion efficiency (PCE) after exposure in ambient conditions. Inverted OPVs comprised of ITO/ZnO/poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PCBM)/Ag demonstrate over 3.5% power conversion efficiency only if the devices are exposed in air for over 4 days. As concluded through a series of measurements, the oxygen presence is essential to obtain fully operational solar cell devices without HTL. Moreover, accelerated stability tests under damp heat conditions (RH=85% and T=65oC) performed to non-encapsulated OPVs demonstrate that HTL-free inverted OPVs exhibit comparable stability to the reference inverted OPVs. Importantly, it is shown that bare Ag top electrodes can be efficiently used in inverted OPVs using various high performance polymer:fullerene bulk heterojunction material systems demonstrating 6.5% power conversion efficiencies

Antimony doped Tin Oxide/Polyethylenimine Electron Selective Contact for reliable and light soaking-free high Performance Inverted Organic Solar Cells

We have demonstrated a high-performance low temperature solution processed electron selective contact consisting of 10 at% antimony doped tin oxide (ATO) and the neutral polymer polyethylenimine (PEI). Inverted organic photovoltaics (OPVs) utilizing ATO/PEI as electron selective contact exhibited high power conversion efficiencies for both the reference P3HT: PCBM and the non-fullerene based P3HT- IDTBR active layer OPV material systems. Importantly it is shown that the proposed ATO/PEI carrier selective contact provides light soaking-free inverted OPVs. Furthermore, by increasing the thickness of ATO layer from 40 to 120 nm the power conversion efficiency of the corresponding inverted OPVs remain unaffected a parameter which indicates the potential of the proposed ATO/PEI carrier selective contact for high performance light-soaking-free and reliable roll-to-roll printing solutions processed inverted OPVs.Comment: 20 pages, 4 figures, 2 table

Inverted Perovskite Photovoltaics Using Flame Spray Pyrolysis Solution Based CuAlO2/Cu−O Hole-Selective Contact

We present the functionalization process of a conductive and transparent CuAlO2/Cu-O hole-transporting layer (HTL). The CuAlO2/Cu-O powders were developed by flame spray pyrolysis and their stabilized dispersions were treated by sonication and centrifugation methods. We show that when the supernatant part of the treated CuAlO2/Cu-O dispersions is used for the development of CuAlO2/Cu-O HTLs the corresponding inverted perovskite-based solar cells show improved functionality and power conversion efficiency of up to 16.3% with negligible hysteresis effect

Nitrobenzene as additive to improve reproducibility and degradation resistance of highly efficient methylammonium-free inverted Perovskite solar cells

We show that the addition of 1% (v/v) nitrobenzene within the perovskite formulation can be used as a method to improve the power conversion efficiency and reliability performance of methylammonium-free (CsFA) inverted perovskite solar cells. The addition of nitrobenzene increased power conversion efficiency (PCE) owing to defect passivation and provided smoother films, resulting in hybrid perovskite solar cells (PVSCs) with a narrower PCE distribution. Moreover, the nitrobenzene additive methylammonium-free hybrid PVSCs exhibit a prolonged lifetime compared with additive-free PVSCs owing to enhanced air and moisture degradation resistance