Season the chicken thighs with salt, pepper, smoked paprika, and garlic powder.
Heat the oil in a skillet over medium-high heat. Sear the chicken skin-side down until deeply golden and crisped slightly.
Transfer the chicken thighs to the slow cooker skin-side up.
In a bowl, whisk together the barbecue sauce, Dr Pepper, brown sugar, Worcestershire sauce, apple cider vinegar, and Dijon mustard.
Pour the sauce around the chicken thighs rather than directly over the skin.
Cover and cook on LOW for 5–6 hours, until the chicken is tender.
During the last 30–45 minutes of cooking, remove the lid so the sauce can thicken and become glossy.
For extra caramelized skin, place the chicken under the broiler for a few minutes before serving.
Spoon the sauce over the chicken and serve warm.