Add to custom helper this dependency

\Magento\Store\Model\App\Emulation $emulation,
...
$this->emulation = $emulation;

and then in code before fetching logo run this

$this->emulation->startEnvironmentEmulation($storeId);

Once you finish what you wanted just restore original environment

$this->emulation->stopEnvironmentEmulation();

Add to custom helper this dependency

\Magento\Store\Model\App\Emulation $emulation,
...
$this->emulation = $emulation;

and then in code before fetching logo run this

$this->emulation->startEnvironmentEmulation($storeId, \Magento\Framework\App\Area::AREA_FRONTEND, true);

Once you finish what you wanted just restore original environment

$this->emulation->stopEnvironmentEmulation();

Add to custom helper this dependency

\Magento\Store\Model\App\Emulation $emulation,
...
$this->emulation = $emulation;

and then in code before fetching logo run this

$this->emulation->startEnvironmentEmulation($storeId);

Once you finish what you wanted just restore original environment

    $this->emulation->stopEnvironmentEmulation();

Add to custom helper this dependency

\Magento\Store\Model\App\Emulation $emulation,
...
$this->emulation = $emulation;

and then in code before fetching logo run this

$this->emulation->startEnvironmentEmulation($storeId);

Once you finish what you wanted just restore original environment

$this->emulation->stopEnvironmentEmulation();