File-Per-Directory.ps1

$Files = Get-ChildItem -Path 'C:\Temp' -Filter "*.tsv" -Recurse
$Directories = $Files | Group-Object -Property 'DirectoryName'

foreach ($Directory in $Directories) {
    $Outfile = Join-Path -Path $Directory.Name -ChildPath '\HTML-File-Name.html'

    # Start your HTML file here, add CSS or headings.
    
    foreach ($File in $Directory.Group) {
        Import-Csv -Delimiter "`t" -Path $File.FillName | ConvertTo-Html | Out-File -FilePath $Outfile -Append
    }
}