Bulk perovskite films have proved to be excellent candidates for photovoltaic devices due to their remarkable optoelectrical properties. However, a major drawback is their relative instability due to rapid degradation and defect formation in ambient conditions. One method of countering these drawbacks is to utilise a thin, 2D perovskite passivating layer on top of a bulk perovskite film, effectively combining the high efficiencies seen in 3D films with the increased stability of 2D films [1]. Whilst such alterations have shown promising results for photovoltaic devices, the feasibility of utilising passivated perovskite films for other applications such as solar energy conversion have not yet been studied.

Incorporating excitonic processes demonstrated by certain organic semiconductors could potentially bypass the detailed balance limit imposed on traditional single junction solar cells [2]. These processes include multiple exciton generation by high energy photons reducing thermalisation losses or by converting multiple low energy, below band-gap photons into one high energy photon. The latter process is commonly referred to as “photon upconversion” and can be achieved in certain organic semiconducting materials via sensitised triplet-triplet annihilation where two spin-1 triplet excitons combine to form one emissive spin-0 singlet exciton.

Due to the high absorption cross-section of bulk perovskite films at near infrared wavelengths they have emerged as promising solid-state sensitisers to generate triplet excitons in an adjacent organic semiconductor film [3], where direct optical generation of triplet excitons is spin-forbidden. In this presentation we present the first observation of bulk perovskite sensitised upconversion using a 2D passivation layer. We investigate the role that the 2D perovskite intermediary layer plays in the upconversion process is in both the impact of the passivating layer on the bulk perovskite and for the upconverting performance of the system. This presentation explores the inherent balance between reduced transport across the interface due to the introduction of a potential barrier versus the reduction of parasitic back transfer by increasing the distance between the strongly absorbing sensitiser and annihilator. Such experimental results raise important questions on the nature of energy transfer across a bulk perovskite/2D perovskite/organic semiconductor interface. This observation holds implications not only for the emerging field of perovskite-sensitised upconversion but also for broader research endeavours exploring interfaces between hybrid and organic semiconductors.