Researchers at the Indian Institute of Technology Bombay, India, have developed bandgap-tunable transparent perovskite solar cells for 4T silicon–perovskite tandem PV. The study has focused on rational interface management by modifying the hole transport layer using ion-modulated spiro-MeOTAD containing TBMPTFSI salt. This modification has replaced conventional LiTFSI and t-BP dopants and has improved interfacial energy alignment while reducing recombination losses. Researchers have evaluated transparent perovskite absorber compositions with bandgaps of 1.52 eV, 1.61 eV, and 1.72 eV. In the 1.52 eV device, open-circuit voltage has increased from 1.08 V to 1.13 V and efficiency from 18.2% to 21.3%. The optimized transparent perovskite cell has been integrated with n-type TOPCon silicon solar cells with standalone efficiency of 25.5%. The resulting four-terminal tandem configuration has achieved power conversion efficiency of 30.2%, representing an 18% relative improvement.