Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces. Interface properties essentially determine the performance of perovskite photovoltaics (PV). Typical electron-transport-layer-free (ETL-free) perovskite PV suffers from significant loss of performance as a result of inferior carrier dynamics at the interface. Here, we determine that the low efficiency of ETL-free perovskite PV is attributed to insufficient photoexcited carrier collection, which originates from the inhibited carrier injection at the interface without a distinct ETL. We found that improving the carrier lifetimes of perovskite films can effectively counterbalance the low-injection-rate interface (e.g., ETL-free interface), enabling efficient carrier collection in ETL-free perovskite PV. By using perovskite films with microsecond carrier lifetimes, we achieved ETL-free PV with >19% efficiency, which makes ETL-free devices comparable to p-i-n-structured perovskite devices. These results indicate a general approach to improving the performance of PV devices with inferior interfaces. The performance of electron-transport-layer-free (ETL-free) perovskite photovoltaics is far more sensitive to the carrier lifetime of perovskite films than analogous ETL-containing devices. A long carrier lifetime can counterbalance the inferior interface in the absence of a distinct ETL, enabling efficient carrier collection in ETL-free perovskite PV. By using perovskite films with microsecond carrier lifetime, Hu and co-workers achieved ETL-free solar cells with >19.5% power conversion efficiency, which is comparable to the analogous value of ETL-containing devices.

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