REVIEW Understanding and harnessing the potential of layered perovskite-based absorbers for solar cells Meenakshi Pegu 1 & Muhammed P. U. Haris 1 & Samrana Kazim 1,2 & Shahzada Ahmad 1,2 Received: 27 August 2020 /Accepted: 16 October 2020 # Qatar University and Springer Nature Switzerland AG 2020 Abstract Hybrid perovskite-based absorbers are promising materials for the fabrication of next-generation thin film photovoltaics, owing to their cost effectiveness and low amount of materials usage. Three-dimensional (3D) perovskite analogues have shown outstanding potential in terms of power conversion efficiency; however, the concern about its long-term stability impede its industrial endeavour. One such approach is the development and employment of lower dimensional, i.e. layered perovskite, structures that aim to achieve an improved stability along with competitive photovoltaic performance. Layered perovskite absorbers also provide a credible pathway of tuning the optoelectronic properties by judicious spacer groups. We highlight the use of layered perovskite-based absorbers and how its microstructure, optoelectronics, charge carrier dynamics influence the photovoltaic properties. Keywords Thin film solar cells . Perovskite solar cells . Layered perovskites . Ruddlesden-Popper phase . Dion Jacobson perovskites . Layered/3D perovskites . Lead-free perovskites 1 Introduction Hybrid organic-inorganic halide perovskites emerged as the competitive candidate for perovskite solar cells (PSCs) fabri- cation, owing to their inexpensive, solution processed route and exceptional photovoltaic (PV) properties stemmed from high absorption coefficients, long charger carrier diffusion length, improved structural and compositional flexibility [1–5]. The current decade has witnessed landmark research progress of perovskites for solar energy conversion in opto- electronic devices and being discussed in the PV industries [6]. At the time of writing of this report, several industrial companies are projecting the production of PSCs in next 1– 2 years [7, 8]. The power conversion efficiency (PCE) has reached notably to 25.5% for a single junction PSCs, and close to 30% in tandem configuration [9]. In a seminal work, three- dimensional perovskite structure was developed by Weber et al in 1978 and the next landmark result was reported by Mitzi and co-workers for its distinctive optoelectronic proper- ties [10, 11]. The hybrid halide perovskite as the light harvest- er was firstly used in dye-sensitized solar cell (DSSCs) by Miyasaka et.al. [12]. The PCE reported was 3.8% and in 2012, Park et al. developed the usage of solid-state hole transporting material (HTM) such as Spiro-OMeTAD and re- ported a PCE of 9.7%; this was followed by another report by Snaith et al. with a PCE of 10% [2, 13]. Different studies led to further optimization of results and improved device perfor- mances was reported [14–18]. Research efforts have been delineated on optimising the selective layers including the perovskite absorber compositions, hole transport layers (HTLs) {such as Spiro-OMeTAD, poly(triarylamine) (PTAA), poly(3,4-ethylenedioxythiophene)-poly(styrene sul- fonate) (PEDOT:PSS)) [19], electron transporting layer, (ETLs) (such as meso-TiO 2 , SnO 2 ,[6,6]-Phenyl C 61 butyric acid methyl ester (PCBM)) and selective contacts (Au, Ag, Cu) depending upon the architecture of the devices [20–22]. Significant focuses were also laid on the long-term stability for commercial exploitation of PSCs by passivating the trap defects, device encapsulation and interface modification [23]. To withstand the stability of the PSCs, compositional Meenakshi Pegu and Muhammed P. U. Haris contributed equally to this work. * Shahzada Ahmad shahzada.ahmad@bcmaterials.net 1 BCMaterials, Basque Center for Materials, Applications and Nanostructures, UPV/EHU Science Park, 48940 Leioa, Spain 2 IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain Emergent Materials https://doi.org/10.1007/s42247-020-00134-w