A projection of worldwide CO₂ emissions of the future PV industry is initially presented. We investigate the development of gross global CO₂-emissions from the PV industry towards a sustainable energy future. This is the basis for our motivation to propose a fully printed integrated carbon-based PV module concept as alternative pathway to strongly reduce the carbon footprint to the ultimate lower limit of the glass substrate fabrication. For this glass-glass sealed perovskite solar cell (PSC) concept in which the perovskite is introduced “in-situ” as a last fabrication step, we show a certified-stabilized efficiency of 9.3 %. We calculated for the in-situ PSC an emission of 3.67 g CO­₂-eq/kWh, which is just 4.8 % of the value for mono-Si PV modules.

With the goal to increase the efficiency towards an ambitious - yet achievable - 20%, we propose three approaches aimed at increasing the light-harvesting efficiency and at obtaining a uni-directional charge transport. These approaches have been experimented on monolithic carbon-based PSCs (C-PSCs):

1. A perovskite molten-salt approach obtained through liquefaction and recrystallization of CH₃NH₃PbI₃ perovskite with methylamine - MA⁰(CH₃NH₂) gas. The fabricated C-PSC showed optimized perovskite self-assembling and improved crystallization with efficient charge transport and extraction, resulting in a high V_OC of 1 V, which is the highest V_OC reported for a monolithic HTL-free MAPbI₃ device. This device has been certified under steady-state with a value of 12.6%. Furthermore, we unravel how methylamine interacts with perovskite during its liquid-to-solid transition by using a combination of Raman spectroscopy, single-crystal XRD and a real-time photoluminescence (PL) monitoring during the crystallization.

2. Monolithic C-PSCs commonly use thick >1 µm printed electrically insulating space layer to prevent charge recombination at the mp‑TiO₂/carbon interface. We show a reproducible large-area procedure to replace this thick space layer with an ultra-thin dense 40 nm sputtered Al₂O₃, which is able to prevent ohmic shunts and to efficiently reduce the charge recombination at the mp-TiO₂/carbon interface. Herewith, transport limitations related so far to the hole diffusion path length inside the thick mesoporous space layer have been omitted by concept. A stable V_OC of 1 V using MAPbI₃ perovskite has been achieved with stabilized device performance of 12.1%.

3. The third approach show how embedding cross-linked poly(methyl-methacrylate) (PMMA) nanoparticles of tunable size into the mesoporous TiO₂ scaffold via sol-gel process can directly influence the pore size of the final film and, therefore, enhance the light-harvesting efficiency. SEM and 3D nano-tomography (from FIB-SEM) demonstrate the pore size engineering of the mp-TiO₂ layer. The impregnated C-PSC filled with double-cation mixed halide FA_0.83Cs_0.17PbI_2.64Br_0.36 perovskite photoabsorber, reaches V_OC close to 1 V with a power conversion efficiency (PCE) of 12.7%.