gap with other emerging photovoltaic technologies. [1][2][3][4] PSCs offer a combination of relevant advantages such as easy manufacturing at low cost, low-energy consumption and high yield manufacturing, compatibility with flexible and lightweight substrates, material/properties tunability (e.g., transparency, color, shape, and so on), low-light sensitivity, reduced environmental impact, and absence of rare or toxic elements. [5][6][7] The enhanced photovoltaic performance, combined with these specific and unique characteristics, confirms the great potential of PSCs as a valid candidate in the competitive market of wearable/ portable electronics and building-integrated photovoltaic. [8][9][10][11] Nevertheless, to fill the gap between laboratory-scale PSCs and real applications, several issues mainly related to device stability and processing need to be solved. [12][13][14] Indeed, the possibility to have reliable PSCs based on stable materials processed by industrially scalable deposition techniques still represents one of the biggest challenges for this technology. In addition, continuous efforts are devoted to rationally design and develop new efficient active materials with additional requirements, such as 1) straightforward synthesis and purification, [15][16][17] 2) intrinsic stability to oxygen/ temperature/light, [18] and 3) processability from "greener" solvents. [19,20] The parallel development of easily processable and environmentally robust functional materials, such as interlayers (ILs), represents another key aspect for the performance and stability of PSCs. ILs (electron or hole transporting layers, ETLs or HTLs, respectively) not only act as efficient charge selective/extracting layers, but also prevent physical and/or chemical interactions between active layer and electrodes. [21,22] Among ETLs, n-type metal oxides (e.g., ZnO, TiO x , SnO x ) are predominant and well-consolidated ILs for the fabrication of standard/inverted PSCs due to their optimal solution processability, intrinsic and ambient stability, optical transparency, and excellent capability to extract/transport electrons. [23,24] On the contrary, one of the most used HTL for PSCs is the conducting polymer PEDOT:PSS due to its excellent processability and electronic/electrical properties, even though its acidity and hygroscopic nature, combined with a phase-segregation tendency, can significantly influence the stability of the resulting