Vol.:(0123456789) 1 3 Applied Physics A (2019) 125:476 https://doi.org/10.1007/s00339-019-2766-7 T.C.: SOLAR ENERGY MATERIALS AND APPLICATIONS Recent progress concerning inorganic hole transport layers for efcient perovskite solar cells Ahmed Mourtada Elseman 1,2  · Sajid Sajid 2  · Ahmed Esmail Shalan 1  · Shaimaa Ali Mohamed 3  · Mohamed Mohamed Rashad 1 Received: 1 May 2018 / Accepted: 17 June 2019 / Published online: 24 June 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Typically, low cost as well as stability factors of the organo-metal halide perovskite solar cells based on inorganic hole transport layers (HTLs) have been the focus of intense research over the past few years. Accordingly, the power conversion efciencies have rapidly been improved to ~ 20% with high stabilities. Therefore, this review covers the major advances of inorganic HTLs in perovskite solar cells that have contributed to the recent efciencies and stabilities, including the evolu- tion of device architecture, the development of hole transport material deposition processes, synthesis, morphology and the interface properties between inorganic HTLs and perovskite layers. Eventually, the challenges and future directions for inorganic HTLs-based perovskite solar cells are also discussed. 1 Introduction The skyrocket development in the photoconversion ef- ciency (PCE) of the organometal halide organic–inorganic hybrid perovskite solar cell (PSCs) has charmed the photo- voltaic community and extended their application to other optoelectronic devices such as a light-emitting diode [1–3], photodetectors [4, 5], semiconductor lasers [6–8] and sen- sors [9] as well as energy storage [10] and water splitting [11]. Add on to their solution processability which repre- sents an optimal route toward thin flm integration and scal- ability for large-scale production. Miyasaka et al. reported the frst overture based on perovskite CH 3 NH 3 PbBr depos- ited on a layer of the nonporous TiO 2 layer with an ef- ciency of 2.2%. In 2009, they were able to achieve 3.5% efciency by replacing bromine with iodine, and use of iodide/triiodide redox electrolyte as a hole transporting medium (HTM) in a dye-sensitized like structure and this was the time when the perovskite came to play a role in the energy conversion devices [12]. Later, Park et al. achieved 6.5% PCE but with miserable stability owing to the used liquid electrolyte [13]. This has then lead to the frst solid- state device that employed scafold mesoporous TiO 2 layer and 2,2′,7,7′-tetrakis-(N,N-p-dimethoxy-phenylamino)-9,9′- spirobifuorene (Spiro-OMeTAD) with a 9.7% PCE [14]. Lee et al. [15] demonstrated 10.9% using the mesoporous alumina Al 2 O 3 as a scafold layer instead of TiO 2 . Sequen- tial deposition of the perovskite flm and light soaking uti- lizing an array of light-emitting diodes at a temperature of 45 °C enable stunning PCE of 15% and increase the device reproducibility [16]. Then, it was solvent engineering for a bilayer architecture and poly(triarylamine) as a hole trans- port material which enables a certifed 16.2% efciency with no hysteresis [17]. The non-wetting surface of the hole trans- port layer (HTL) drives the high-aspect-ratio crystallization of the organolead trihalide perovskite flms, suppressed the heterogeneous nucleation and reduced the grain boundary which results in a crystallinity and stability improvement and a notable reduction in the charge recombination accounting for 18.3% PCE [18]. Delicate control over the carrier dynam- ics suppressed carrier recombination and maintained proper carrier extraction at the electrodes for the device fabricated at the air with superior efciency of 19.3% reported by Zhou * Mohamed Mohamed Rashad rashad133@yahoo.com 1 Advanced Materials Division, Electronic and Magnetic Materials Department, Central Metallurgical Research and Development Institute (CMRDI), P.O. Box 87, Helwan, Cairo 11421, Egypt 2 State Key Laboratory of Alternate Electrical Power, System with Renewable Energy Sources, School of Renewable Energy, North China Electric Power University, Beijing 102206, China 3 Center for Photonics and Smart Materials, Center for Nanotechnology, Zewail City of Science and Technology, October Gardens, 6th of October City, Giza, Egypt