Researchers from the Indian Institute of Technology (IIT) Guwahati have designed a multilayer photonic film that both lets more usable sunlight reach a perovskite solar cell and passively cools it, together delivering an absolute power conversion efficiency (PCE) improvement of 3.76 percentage points.
Heat is a persistent problem for solar cells: perovskite solar cells (PSCs) tolerate moderate temperature increases better than crystalline silicon cells, but beyond about 55°C their efficiency drops off faster than silicon's does, and a cell's aging rate roughly doubles for every 10°C rise in operating temperature. Passive radiative cooling offers a way to manage this without consuming any power, by using materials that emit heat efficiently in the "atmospheric window" (8-13 micron wavelengths), a band where the atmosphere is largely transparent and heat can radiate straight out to the cold of space.
The team's film takes this a step further by combining that cooling function with active light management, rather than treating them as separate problems. It consists of an all-dielectric multilayer stack deposited on a flexible PET substrate, with each layer's thickness tuned using an adaptive particle swarm optimization algorithm. Because a perovskite absorber can only convert light above its bandgap energy into electricity, the design lets the useful, higher-energy portion of sunlight pass through efficiently (85.1% average transmittance) while reflecting away the longer, sub-bandgap wavelengths that would otherwise just heat the device without generating current (69.8% average reflectance in that range), and radiating absorbed heat back out efficiently (96.5% average emissivity).
Tested on a conventional perovskite solar cell, letting more usable light through increased the cell's photocurrent, contributing a 1.07 percentage-point absolute efficiency gain on its own. Combined with the passive cooling effect, which lowered the cell's operating temperature by around 10°C, the full design delivered the overall 3.76 percentage-point absolute efficiency improvement.
The researchers also note that the film's performance is polarization-independent and stays consistent across incidence angles up to 60 degrees, and that its lithography-free, scalable fabrication process keeps it low-cost. Because it works as an add-on layer rather than requiring changes to the underlying device architecture, the team positions it as a practical route to improving both efficiency and operational lifespan for flat and flexible perovskite solar cells alike.
