Since the conversion efficiency of silicon (Si)-based solar cells stagnates at 26.7% in the literature, extensive research and development activities are carried out on perovskite silicon-based tandem solar cells. However, the presence of lead (Pb) and the instability of perovskite prevent their large-scale implementation in the photovoltaic industry. Therefore, it is important to replace the hazardous material (Pb) in perovskite top cells to design non-toxic perovskite–silicon tandem solar cells. The current work yields much-needed studies to develop a non-toxic perovskite–silicon-based tandem solar cell. For the first time, methylammonium tin mixed halide (MASnI3–x Br x )-based materials are comprehensively investigated and optimized with respect to different halide compositions, absorber layer thickness, and bulk defect density in standalone configurations, followed by the development of a lead-free MASnI2Br1–Si-based tandem solar cell. The transfer matrix method and current matching techniques are used to design the two-terminal monolithic tandem cell, which showed a maximum conversion efficiency of 30.7% with an open circuit voltage (V OC) of 2.14 V. The results outlined in this manuscript will pave the way for the progress of highly efficient, non-toxic perovskite–silicon tandem solar cells.

Photovoltaic solar cells based on perovskite materials due to their unique optoelectronic properties are good instruments to develop green energy for worldwide energy demands. In perovskite solar cells (PSCs), a high performance of 25.8% was reported, employing an expensive Spiro-OMeTAD hole transport layer. Here, the study is focused on PSCs without any HTLs (HTL-free PSCs) to reduce the fabrication process costs. The electron transport layers (ETLs) are treated with tetramethylammonium hydroxide (TMAOH) to improve the efficiency of HTL-free devices. By employing a treatment step, the conductivity of ETLs is increased while their transparency is kept safe. The improved conductivity leads to accelerated charge transport within the device and reduces electron−hole recombination. The perovskite layers fabricated on the treated ETLs showed lower surface defects due to better spreading of the perovskite solution on them. The reduced surface defects cause improvements in the photovoltaic performance of HTL-free PSCs, leading to a stability increment due to lower surface defects for the reaction of humidity with the perovskite layer. TMAOH treatment results in PSCs with a maximum PCE of 13.24%, higher than the 10.88% for control devices.

Hole transport material-free perovskite solar cells (HF-PSCs) offer low-cost photovoltaic devices. For development and commercialization, they are more attractive than the expensive HTLcontained perovskite solar cells. Herein, we focused on enhancing the stability and efficiency of HF-PSCs with the malonic acid (MA) addition to the methylammonium lead iodide. The introduced additive increases the perovskite crystallinity and assembles a perovskite layer with larger grains along with fewer surface defects. In addition, the MA-modified HF-PSCs show suppressed charge recombination within devices, and a lower charge trap density has been obtained for them. A considerable power conversion efficiency of 14.14% is achieved for MA-modified HF-PSCs, higher than the performance of 11.88% for the untreated HF-PSCs. Finally, MA-based HF-PSCs show higher shelf stability than the control HF-PSCs. It is because the MA-modified perovskite layer with passivated grain boundaries is better at repelling water.

Tandem solar cells have higher efficiency than single-junction devices owing to their wide photon absorption range. A wide band gap (Eg) absorber absorbs the higher-energy photons in the top cell. In contrast, a comparatively low band gap absorber material is utilized in the bottom cell to absorb the filtered low-energy photons. Consequently, thermalization and transparent energy losses are overshadowed by the top subcell (Topsc) and the bottom subcell (Bottomsc), respectively. However, to achieve the best efficiency from a tandem design, the choice of active material in the Topsc and the Bottomsc plays an important role. Therefore, in this proposed study, a tandem solar cell comprising a perovskite (Eg 1.68 eV)-based top cell and a copper indium gallium selenide (CIGS, Eg 1.1 eV)-based Bottomsc has been designed and analyzed. A state-of-the-art Me-4PACz ([4-(3,6-dimethyl-9H-carbazol-9-yl)­butyl] phosphonic acid) hole transport layer (HTL) in the perovskite solar cell reported in the previous literature has been considered for the top cell, whereas a calibrated CIGS-based Bottomsc with 16.50% efficiency is designed. Both the Topsc and the Bottomsc are examined for the tandem configuration using filtered spectra and current-matching techniques. In perovskite/CIGS tandem design, an ideal tunnel recombination junction uses Me-4PACz and ITO layers. In a tandem configuration with matched current density at an absorber thickness of 347 nm for Topsc and 2.0 μm for Bottomsc, the device delivered an open-circuit voltage (V OC), current density (J SC), and fill factor (FF) of 1.92 V, 20.04 mA/cm2, and 77%, respectively, resulting in an overall power conversion efficiency (PCE) of 29.7%. The results reported in this work would be beneficial for the development of perovskite-CIGS-based monolithic tandem solar cells in the future.

In this digital simulation, tin-based with the use of CeOx as an ETL with varying percentages of oxygen has been investigated.