Why does using an & in data or class = formula fields interfere with wb_add_data in OPENXLSX2

Question

I'm attempting to write a small table of formulas to an excel sheet. It works perfectly except if I try to use "&" characters. Here's my code:

First I add a worksheet called Summary, build a dataframe that I'll populate with formulas and add it to the workbook.

if(exists("df_tmp")) {rm(df_tmp)}
a <- c("Above and Beyond", "Fully Met", "Partially Met", "Did Not Meet") # try using "&" instead of  "and"
b <- c(.15, .70, .10, .05);
c <- c("","","","")
d <- c("","","","")
e <- c("","","","")
f <- c("","","","")
df_tmp <- data.frame(a,b,c,d,e,f)

## Add Formula(s): Summary Table ----
wb <- wb_workbook()
wb$add_worksheet("Summary")

df_tmp$c = paste0('F',seq(4,7),'/SUM($F$4:$F$7)')
df_tmp$d = paste0('ROUNDDOWN((COUNTA(Population!A:A)-1)*C',seq(4,7),',0)')
df_tmp[1,5] = paste0('COUNTIF(Population!G:G,"Above and Beyond")') # try using "&" instead of "and"
df_tmp[2,5] = paste0('COUNTIF(Population!G:G,"Fully Met")')
df_tmp[3,5] = paste0('COUNTIF(Population!G:G,"Partially Met")')
df_tmp[4,5] = paste0('COUNTIF(Population!G:G,"Did Not Meet")')
df_tmp$f = paste0('E',seq(4,7),'-F',seq(4,7))

class(df_tmp$c) <- c(class(df_tmp$c), "formula")
class(df_tmp$d) <- c(class(df_tmp$d), "formula")
class(df_tmp$e) <- c(class(df_tmp$e), "formula")
class(df_tmp$f) <- c(class(df_tmp$f), "formula")

colnames(df_tmp) <- c("Rating","Target Percentage","Actual Percentage", "Target Count", "Actual Count", "Δ to Meet Distribution Targets")
wb <- wb %>% wb_add_data(sheet = "Summary", df_tmp, dims = wb_dims(3, 2))
if (interactive()) wb$open()

This code works perfectly. However, if I replace the "and" with an "&" in the strings indicated above, the workbook errors. I've tried escaping it with "\" but no matter what I try, I get this error when attempting to open the workbook:

Any thoughts? The ampersand & is an unfortunate requirement for me as these workbooks process input data over which I have no control. Hopefully I'm skipping something obvious. Thank you for your wisdom!