Researchers from Zhejiang University, Shanghai University of Electric Power, Zhejiang Zheneng Wenzhou Power Generation Co., and Ningbo University of Technology have reported significant progress in tin-based, hole-transport-layer-free (HTL-free) perovskite solar cells (PSCs). Their study introduces a gradient doping strategy to enhance the optoelectronic properties of MASnI₃ absorbers through precise band engineering, achieving remarkable efficiency improvements verified by SCAPS-1D numerical simulations.
Tin-based PSCs have emerged as promising candidates for eco-friendly and lead-free photovoltaics due to tin’s non-toxic nature and favorable semiconductor characteristics, including high carrier mobility and optimal bandgaps. Yet, eliminating the traditional HTL has historically reduced device performance. The team’s approach directly tackles this limitation by creating a controlled doping gradient within the absorber, generating an internal electric field that boosts charge separation and transport efficiency.
Numerical modeling using SCAPS-1D explored how factors such as absorber thickness, doping profile, defect density, and contact material influence device behavior. The optimal configuration featured an absorber layer thickness of 1000 nm and a defect density of 1×1015 cm⁻³. Even with only two sublayers, gradient doping substantially improved power conversion efficiency (PCE) from 20.09% (uniform doping) to 24.48%. When electron transport layers and back electrodes were further optimized, the device achieved a VOC of 1.07 V, JSC of 32.566 mA/cm², fill factor (FF) of 80.02%, and final PCE of 25.81%.
The mechanism behind these gains lies in band alignment and charge carrier dynamics. The gradient doping structure establishes a built-in potential across the absorber, effectively reducing interfacial energy barriers and ensuring faster extraction of photo-generated electrons and holes. This minimizes carrier recombination losses, stabilizes operation, and increases efficiency without relying on costly organic HTLs.
This research demonstrates that rational design of doping gradients can be a viable route toward developing high-efficiency, stable, and environmentally friendly tin-based perovskite solar cells - a milestone on the path toward sustainable, low-cost photovoltaic technologies.
