The winning future of the emerging perovskite (PSK) solar cells is closely linked to the dimension scalability and the possibility to boost the existing photovoltaic (PV) technology employing tandem architectures.[1] The synergetic development of large area PSK devices fitting the standard silicon wafer dimensions and the optimization of PSK/silicon tandem architectures can definitively open up new horizons for winning the commercialization challenges. To this end, bi-dimensional (2D) materials recently demonstrated their effectiveness in boosting the PSK PV device efficiency and stability by mitigating the performance drop when scaling the cell dimensions up to module size.[2] In particular, transition metal carbides, nitrides and carbonitrides (MXenes) having a general formula M_n+1X_nT_x (n = 1, 2, 3), where M represents an early transition metal, X is carbon and/or nitrogen, and T_x stands for surface terminations (such as OH, O, F or alternatively Cl) have been used in perovskite-based devices with different aims. During their synthesis, their surfaces are naturally functionalized, by significantly shifting the WF in a broad range form 1.6 to 6 eV.[3] Recently we demonstrated a general approach where Ti₃C₂T_X MXenes can be employed as dopant of the perovskite precursor solution to shift the perovskite layer work function by achieving a proper energy level alignment at perovskite/charge transporting layer (CTL) interfaces, eventually passivating perovskite bulk and interfacial defects.[4][5] This resulted in Mxene-engineered large area perovkite opaque module (PSM) demonstring PCE overcoming 17% and 15% over 121 cm² and 240 cm² substrates area respectively.[6]. When moving from the opaque to semi-transparent (ST) devices employed in tandem configuration, the absence of the light backscattering by the metal counter electrode (here replaced by a ST one) and to an enlarged band-gap (from 1.68 to 1.72 in case Si-based cells are employed as bottom technology) led to a not-negligible reduction of the ST-perovskite cell (ST-PSC) short circuit current (J_SC).[7] In this case, we proposed the use of Ti₃C₂Cl₂ MXenes where, a strong coordination between Cl atoms and Pb²⁺ ions was established, resulting in a reduction of metallic lead clusters (Pb⁰) responsible for the formation of deep defects and trap free charge carriers in the perovskite films. Moreover, the interaction between the MXene Cl terminations and the perovskite Pb²⁺ ions formed an adduct with the perovskite precursor, acting as heterogeneous nucleation site for the perovskite film. The resulting perovskite film showed a more pronunced n-character (WF tuning) and enlarged grain size with increased absorbance, translating in ST-PSCs with increased J_SC. The as optimized ST-PSC showed PCE exceeding 18% while ST large area modules (ST-PSM) achieved PCE surpassing 16% over 90 cm² substrate area.

The MXene-based ST-PSMs (4 parallel-connected modules) have been coupled with wafer sized (15.7x15.7 cm²) commercial silicon heterojunction (Si-HJT) bifacial cells, in a 4 terminal (4T) architecture by realizing a 20x20cm² PSK/silicon tandem mini-panel with PCE above 20%. Moreover, the power generated density (PGD) has been estimated to be > 23 mW/cm² considering a typical radiation of 30%. The modular architecture proposed for the tandem mini-panel, can represent a building block to develop larger 4T tandem panels, with minimized PCE losses. Following this approach, on one side the PSK solar modules can be independently optimized, realized and stacked atop the commercial Si-HJT cells employing an ad-hoc developed lamination process. On the other side, the as-proposed panel architecture does not require any modification in the Si production lines, making the tandem technology appealing for the already exiting Si cell producers.