Increasing and controlling the charge carrier density is fundamental for optimizing the performance of optoelectronic devices, such as light emitting diodes and field effect transistors. As a method to increase carrier density, doping is highly efficient and well understood in inorganic semiconductors. In contrast, molecular doping of organic semiconductors (OSCs) remains the subject of intense research activities and is not fully understood yet. The most common approach of molecular doping is to introduce dopant molecules that accept electrons from or donate electrons to the OSC, formally known as p-type and n-type doping leaving positive or negative charge carriers (polarons) in the OSC material, respectively. In recent years, tremendous experimental progress has been made in improving and understanding the molecular p-type doping, but their performance is limited due to limitations in solubility, doping efficiency, and hole mobility of the commonly used molecular dopants such as for example F 4 TNCQ (tetracyano-2,3,5,6-tetrafluoroquinodimethane). Lewis acid doping was proposed as an alternative that partially overcomes these limitations in P3HT (poly(3-hexylthiophene)). As recently reported by Yurash et al., the doping of the polymer PCPDT-BT (poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1b;3,4-b']dithio phene)-alt-4,7(2,1,3-benzothiadiazole)]) with the strong Lewis acid BCF (tris(pentafluorophenyl)borane) exceeds the doping achieved using traditional molecular p-type doping with F 4 TNCQ. As for the origin of doping via BCF a multi-step mechanism was proposed. First, a Brønsted-type acid BCF:H 2 O complex is formed in solution which is then capable of protonating the polymers backbone and leaves behind a BCF:OH -counter anion. In a second step, an intermolecular electron transfer occurs in which a neutral polymer chain donates an electron to the protonated polymer chain, leaving a (positive) polaron on the unprotonated polymer chain. The formation of polaronic states is confirmed by UV-Vis-NIR spectroscopic measurements and EPR and ENDOR measurements reveal the presence of unpaired electrons. Recent measurements on a related polymer, PCPDT-BT-SO 3 K, which can be protonated by H 2 O, show similar results. Detailed insights into the effect of Brønsted-type acid complex formation of BCF on the doping of P3HT were obtained identifying the complex formation as the driving factor of polaron formation, confirming the proposed mechanism. Theoretical investigations on the protonation pathway propose that a BCF:HO - counter anion energetically disfavor the protonation of PCPDT-BT, but formation of a [BCF:HO:BCF] -or [BCF:HO:H 2 O:BCF] - counter anion open an exergonic pathway and thus favors the protonation. In the present work we set out to further clarify the microscopic processes underlying Lewis acid doping on a molecular level. To this end, we theoretically analyze the influence of protons on the electronic properties of the widely used copolymer PCPDT-BT, with a particular focus on the protonation-induced charge transfer and polaron formation that may occur. This includes studies on the role of the counter ion in the doping process as well as intra-and inter-polymer chain charge transfer processes. We calculate vibrational infrared spectra showing clear polaron signatures in the form of particularly intense vibrational modes (IVMs) and we calculate vertical excitation spectra to support the interpretation of the experimentally measured spectra. Our results explicitly show that both single and double protonation of polymer chains may well contribute to the Lewis acid doping signatures observed experimentally, with the double doping inducing less localized and potentially more mobile charge carriers.