Perovskite solar cells (PSCs) can achieve high power conversion efficiencies but usually rely on vacuum-deposited metallic contacts, leading to high material costs for noble metals and stability issues for more reactive metals. Carbon-based materials offer a cost-effective and potentially more stable alternative. The vast majority of carbon-electrode PSCs use the negative-intrinsic-positive (n-i-p) or “hole-transport-layer-free” architectures.
Recently, researchers at the University of Oxford, Imperial College London, Philipps-University Marburg, Swansea University and Fraunhofer ISE conducted a systematic study to assess the compatibility of “inverted”, p-i-n configuration PSC contact layers with carbon top electrodes.
The scientists found that a specific combination of materials processed on top of the perovskite layer enables effective fabrication and operation of p-i-n perovskite solar cells by using carbon top electrodes. The difference in the electronic contact behavior of carbon and metal electrodes in p-i-n devices has long been overlooked and has possibly impeded the field’s progress in the direction of p-i-n devices with carbon-based electrode materials. Most common electron transport layers in p-i-n devices are either incompatible or severely damaged by the carbon blade-coating process.
To overcome these issues, the scientists introduced a double-layer atomic layer deposited tin oxide (SnO2) and Poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) (PEDOT:PSS), that enables an ohmic contact with a carbon electrode in a p-i-n stack. The SnO2 layer prevents the removal of the underlying PCBM layer, while the conductive PEDOT:PSS interlayer enables the formation of good electronic contact between the SnO2 and carbon and improved electron extraction in the devices. This yielded up to 16.1% PCE and a retained 94% performance after 500 h of outdoor aging.
The study is a step forward for printable, metal-electrode-free, and evaporation-free perovskite PV technologies.
