Reducing nonradiative recombination in perovskite solar cells with a porous insulator contact

Abstract

Inserting an ultrathin low-conductivity interlayer between the absorber and transport layer has emerged as an important strategy for reducing surface recombination in the best perovskite solar cells. However, a challenge with this approach is a trade-off between the open-circuit voltage ( V _oc ) and the fill factor (FF). Here, we overcame this challenge by introducing a thick (about 100 nanometers) insulator layer with random nanoscale openings. We performed drift-diffusion simulations for cells with this porous insulator contact (PIC) and realized it using a solution process by controlling the growth mode of alumina nanoplates. Leveraging a PIC with an approximately 25% reduced contact area, we achieved an efficiency of up to 25.5% (certified steady-state efficiency 24.7%) in p-i-n devices. The product of V _oc × FF was 87.9% of the Shockley-Queisser limit. The surface recombination velocity at the p-type contact was reduced from 64.2 to 9.2 centimeters per second. The bulk recombination lifetime was increased from 1.2 to 6.0 microseconds because of improvements in the perovskite crystallinity. The improved wettability of the perovskite precursor solution allowed us to demonstrate a 23.3% efficient 1-square-centimeter p-i-n cell. We demonstrate here its broad applicability for different p-type contacts and perovskite compositions.

Through thick but not thin

To maintain high charge carrier conductivity in perovskite solar cells, the passivating layer is usually very thin (~1 nanometer) to enable electron tunneling. However, this approach limits efficiency because it creates a trade-off between open-circuit voltage and fill factor and challenges in fabricating thin films from solution over large areas. Peng et al . grew a thick (~100 nanometer) dielectric mask formed by depositing alumina nanoplates and thus created random nanoscale openings for carrier transport. This layer reduced nonradiative recombination and boosted power conversion efficiencies from 23 to 25.5% compared with a conventional passivation layer. —PDS

Abstract

A solution-processed thick dielectric mask with nanoscale openings can maintain both open-circuit voltage and fill factor.