Indium tin oxide (ITO) is typically used as the bottom contact (anode) in conventional configuration organic solar cells. ITO has a high work function around 4.8 eV, which is very dependent on washing treatments.91,92 However, these variations and the roughness of the resulting films usually result in important contact losses.93 In order to improve the quality of this contact and favor the formation of an ohmic contact, a p-type PEDOT:PSS interlayer, which has a work function of 5 eV, has been traditionally used.94 Due to the acidic nature of PEDOT:PSS and its tendency of being easily degraded in contact with either air or moisture and negatively affecting the stability of the whole device, different transition metal oxides, such as , , , and NiO, which are considered more stable, were introduced as alternative p-type interlayers in relatively highly efficient and stable devices.27,95,96 In the cathode side, instead, calcium was initially inherited from the organic light emitting diode (OLED) development as the hole blocking layer due to its low work function. In spite of the good results obtained for photovoltaic devices in combination with silver, it is, however, very reactive to oxygen and moisture and, thus, device stability is further jeopardized. Therefore, alternative inorganic low work function interlayers were introduced. On one side, inorganic salts, such as LiF,97–99 CsF,100,101 and MgF,102 have been vacuum evaporated in combination with aluminum in order to enhance the contact selectivity and, hence, the PCE. It is believed that due to their high internal dipole moment, thin layers of these materials are able to alter the electrode work function by inducing a shift of the vacuum energy level. Regardless of the increase in efficiency obtained with the use of these materials, they are principally vacuum deposited, which hinders the way toward lower-cost devices based on R2R processing. Solution processable alternatives make use of salts like ZnS,103 LiAc,104 or .105–107 Furthermore, polymeric salt compounds, known as polyelectrolytes, have been used with promising results.108 Also, small molecules with opposing internal charges, zwitterions, have been demonstrated as interfacial layers in organic solar cells.109,110 Khan et al. demonstrated efficient conventional configuration P3HT:ICBA based solar cells substituting the Ca layer with a thin film of a hydrophilic polymer processed from a polyethylenimine, 80% ethoxylated solution, PEIE.111 As a result, devices with a of 0.78 V, of , FF of 65%, and PCE of 4.6% were achieved.