$source = "R:\"
Get-ChildItem -LiteralPath $source -File | ForEach-Object {
    $year = $_.LastWriteTime.Year.ToString()
    $dest = Join-Path $source $year
    if (-not (Test-Path -LiteralPath $dest)) { New-Item -Path $dest -ItemType Directory | Out-Null }
    Move-Item -LiteralPath $_.FullName -Destination $dest
}