Save high quality version of sanky plot

Question

I have this code:

# Libraries
library(tidyverse)
library(viridis)
library(patchwork)
library(hrbrthemes)
library(circlize)
library(webshot)

# Load dataset from github
data <- read.table("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/13_AdjacencyDirectedWeighted.csv", header=TRUE)
# Package
library(networkD3)

# I need a long format
data_long <- data %>%
  rownames_to_column %>%
  gather(key = 'key', value = 'value', -rowname) %>%
  filter(value > 0)
colnames(data_long) <- c("source", "target", "value")
data_long$target <- paste(data_long$target, " ", sep="")

# From these flows we need to create a node data frame: it lists every entities involved in the flow
nodes <- data.frame(name=c(as.character(data_long$source), as.character(data_long$target)) %>% unique())

# With networkD3, connection must be provided using id, not using real name like in the links dataframe.. So we need to reformat it.
data_long$IDsource=match(data_long$source, nodes$name)-1 
data_long$IDtarget=match(data_long$target, nodes$name)-1

# Make the Network
sankey <- sankeyNetwork(Links = data_long, Nodes = nodes,
              Source = "IDsource", Target = "IDtarget",
              Value = "value", NodeID = "name", 
              sinksRight=FALSE, nodeWidth=40, fontSize=13, nodePadding=20)

# you save it as an html
saveNetwork(sankey, "C:\\Users\\brett\\OneDrive\\Desktop\\sankey_diagram.html")

# you convert it as png
webshot("C:\\Users\\brett\\OneDrive\\Desktop\\sankey_diagram.html","C:\\Users\\brett\\OneDrive\\Desktop\\sankey_diagram.png", vwidth = 1000, vheight = 900)

which makes this:

I have to put something this in a scientific poster and the quality of this looks pretty low, Is there any way to make a higher resolution image (eg more dpi) or a tiff, something like that?