Title | Optimization of wide-bandgap perovskite absorbers for all-perovskite tandem solar cells
Date | May 15, 2023
Abstract |Solar cells based on metal-halide perovskite (PK) materials have received much attention the last decade due to their i) high power conversion efficiency (PCE), ii) tunable bandgap energy and iii) low fabrication cost compared to other thin-film and silicon photovoltaic technologies. Moreover, integrating wide-bandgap (WBG) PK materials into tandem solar cell architectures with narrow-bandgap (NBG) absorbers such as silicon, copper indium gallium diselenide and PK, has further boosted the PCE and the PK-based solar cells represent the fastest developing photovoltaic technology to date.
In this talk, we focus on the PKWBG/PKNBG tandem solar cells, which have now reached the impressive 27.4 % solar cell efficiency1, and we discuss different methods to further improve the PCE. The most commonly used strategies to increase the tandem solar cell performance include : i) the introduction of additives into the PK bulk material to decrease the recombination losses within the bulk, ii) the PK/charge transport interface improvement, i.e. the PK/electron- or hole- transport interface (PK/HTL and PK/ETL respectively) and iii) charge recombination junction engineering. Here, we examine the PKWBG/ETL interface and we seek to decrease the open-circuit voltage (Voc) losses caused by charge recombination phenomena at the interface and poor energetic band alignment.
Our main studies to improve the PKWBG/ETL interface are performed on single junction solar cells : soda-lime glass/Indium Tin Oxide (ITO)/ [2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2-PACz)/(Cs,FA)Pb(I,Br)3/C60/Bathocuproine (BCP)/Ag, where (Cs,FA)Pb(I,Br)3 (FA : formamidinium) is the WBG absorber of 1.73 eV and C60 is the ETL layer. The PKWBG/ETL interface often presents : i) dangling bonds at the PK surface that act as charge recombination centers, ii) charge accumulation and ion migration at the interface that lead to hysteresis phenomena and iii) poor energy band alignment causing inadequate charge extraction or/and charge recombination. Hence, PK surface treatments are among the most widely used strategies to improve the PKWBG/ETL interface quality.
In this talk, we discuss different PK surface treatments that minimize the charge recombination losses at the interface such as i) the formation of 2D PK layer using FAI or GABr (GA : guanidinium) spin-coating processes or ii) the introduction of thin AlxOy layer using Atomic Layer Deposition. Our findings show that a thin AlxOy layer leads to an impressive increase of the Voc value by around 100 mV. The optimized PKWBG/ETL structure is then integrated into the PK/PK tandem architecture. Our preliminary results show Voc values higher than 1850 mV and good voltage addition of the two PK subcells.
