| Tin oxide (SnO₂) | Electrons | Perovskite solar cells | Can form a compact, low-temperature electron-selective layer; commonly used in planar device designs. | Surface and interface defects can promote recombination. Surface treatment and good energy-level alignment matter. |
| Titanium dioxide (TiO₂) | Electrons | Perovskite and dye-sensitized solar cells | Well-established electron-selective material, including in mesoporous architectures. | Some processing routes require high-temperature treatment. Interfaces and exposure to ultraviolet light can affect device stability. |
| Fullerene-based layers (such as C₆₀) | Electrons | Perovskite and organic solar cells | Can provide efficient electron extraction and reduce interfacial charge accumulation in suitable device structures. | Often deposited as thin layers; performance depends on contact coverage, interface quality, and compatibility with the absorber. |
| Zinc oxide (ZnO) | Electrons | Organic and perovskite solar cells | Offers electron-selective transport and can be made using solution-based processing. | Surface chemistry can be incompatible with some perovskite compositions or interfaces; surface modification may be needed. |
| Nickel oxide (NiOₓ) | Holes | Perovskite solar cells | Inorganic hole-selective contact that can support thermally robust device designs. | Conductivity, surface defects, and energy-level alignment vary with composition and processing; interface passivation can be important. |
| PTAA (a hole-transporting polymer) | Holes | Perovskite solar cells | Can provide selective hole extraction and is used in high-performance device architectures. | Its properties depend on film formation and interface design; conductivity and contact quality must be adequate for the device. |
| Spiro-OMeTAD | Holes | Perovskite solar cells | A widely studied organic hole-transport material with established use in perovskite devices. | Conductivity is commonly enhanced with additives. Additive choice and environmental sensitivity can affect long-term stability. |
| Passivating selective contacts (for example, SiOₓ/poly-Si or a-Si:H contacts) | Electrons or holes, depending on contact design | Crystalline-silicon solar cells | Combine carrier selectivity with surface passivation, helping limit recombination at silicon contacts. | Contact design and processing must be tailored to the carrier being collected; these are not interchangeable with conventional perovskite transport layers. |