Uncovering the individual JV curves of fully evaporated Perovskite

FEDERICO VENTOSINOS; SOFIA CHOZAS BARRIENTOS; HENK J. BOLINK

Boston

Congreso; MRS Fall Meeting; 2023

Materials Research Society

Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve high power conversion efficiencies at low cost, with already proven devices exceeding 33%. Despite the ever-increasing performance and the improved stability of perovskite solar cells, there is need for characterization techniques for these complex structures to fully understand and optimize them. This becomes a challenge in 2 terminal (2T) tandem devices given the nature of the series connection between them. Due to this junction, the density current in the JV curve corresponds to the minimum of both subcells, while the total voltage is the sum of each subcell. This implies that knowing the short circuit current density (Jsc), the open circuit voltage (Voc) and the fill factor (FF) of the full device does not translate into knowing the individual behavior of each subcell. In the case of Jsc, quantum efficiency measurements with light and voltage biasing can be used to reveal the behavior of each subcell. Sun-Voc with selective illumination can also give approximate values of individual Vocs in the case of very good selectivity. However, it is difficult to obtain information about the FF for each subcell. In this communication we show how a technique developed for studying tandem devices based on thin film silicon materials can be applied to our fully evaporated perovskite on textured silicon 2T tandem devices. To accomplish this, an extra source of illumination (a laser for each subcell in our case) is used to to keep one of the subcells at its Voc while changing the working point at 1 sun illumination of the full stack, hence, revealing the behavior of the other subcell. This allows us to re-construct each subcell individual JV curve of each subcell at 1 sun illumination, giving direct access to all the relevant parameters.I will explaine how the technique works and what are the underlying assumptions and limitations. Particularly, I will discuss the relevance of having good selectivity (meaning, generating voltage in only one of the subcells) and how to solve this issue in the case of poor selectivity. Secondly, I will point out how an extra procedure is needed, since perovskite based solar cells suffer from known issues, such as ion migration and scan rate dependency, from which silicon based tandem devices did not suffer. To overcome these problems, we will propose a methodology that ensures the reliability of the constructed individual JV curves. Finally, we show this method for our vacumm deposited perovskite tandem solar cells, highlighting the evolution of the main parameters (Voc, Jsc and FF) as a function of light soaking time.