Hole‐transporting layers (HTLs) are an essential component in inverted, p–i–n perovskite solar cells (PSCs) where they play a decisive role in extraction and transport of holes, surface passivation, ...perovskite crystallization, device stability, and cost. Currently, the exploration of efficient, stable, highly transparent and low‐cost HTLs is of vital importance for propelling p–i–n PSCs toward commercialization. Compared to their inorganic counterparts, organic HTLs offer multiple advantages such as a tunable bandgap and energy level, easy synthesis and purification, solution processability, and overall low cost. Here, recent progress of organic HTLs, including conductive polymers, small molecules, and self‐assembled monolayers, as utilized in inverted PSCs is systematically reviewed and summarized. Their molecular structure, hole‐transport properties, energy levels, and relevant device properties and resulting performances are presented and analyzed. A summary of design principles and a future outlook toward highly efficient organic HTLs in inverted PSCs is proposed. This review aims to inspire further innovative development of novel organic HTLs for more efficient, stable, and scalable inverted PSCs.
Inverted perovskite solar cells (PSCs) attract great attention due to their low‐temperature processing, negligible hysteresis, and superior stability. For these devices, hole‐transport layers play a decisive role in carrier extraction, transport, and perovskite crystallization. This review provides a comprehensive overview of the structural engineering of organic hole‐transport layers utilized in inverted PSCs including conductive polymers, small molecules, and emerging self‐assembled monolayers.
We report on bulk-heterojunction (BHJ) organic photovoltaics (OPVs) based on the self-assembled monolayer (SAM) 2PACz as a hole-selective interlayer functionalized directly onto the indium tin oxide ...(ITO) anode. The 2PACz is found to change the work function of ITO while simultaneously affecting the morphology of the BHJ deposited atop. Cells with PM6:N3 BHJ and ITO-2PACz anode exhibit a power conversion efficiency (PCE) of 16.6%, which is greater than that measured for bare ITO (6.45%) and ITO/PEDOT:PSS (15.94%) based devices. The enhanced performance is attributed to lower contact-resistance, reduced bimolecular recombination losses, and improved charge transport within the BHJ. Importantly, the ITO-2PACz-based OPVs show dramatically improved operational stability when compared with PEDOT:PSS-based cells. When the ITO-2PACz anode is combined with the ternary PM6:BTP-eC9:PC71BM BHJ, the resulting cells exhibit a maximum PCE of 18.03%, highlighting the potential of engineered SAMs for use in hole-selective contacts in high-performance OPVs.
Perovskite/silicon tandem solar cells are increasingly recognized as promising candidates for next‐generation photovoltaics with performance beyond the single‐junction limit at potentially low ...production costs. Current designs for monolithic tandems rely on transparent conductive oxides as an intermediate recombination layer, which lead to optical losses and reduced shunt resistance. An improved recombination junction based on nanocrystalline silicon layers to mitigate these losses is demonstrated. When employed in monolithic perovskite/silicon heterojunction tandem cells with a planar front side, this junction is found to increase the bottom cell photocurrent by more than 1 mA cm−2. In combination with a cesium‐based perovskite top cell, this leads to tandem cell power‐conversion efficiencies of up to 22.7% obtained from J–V measurements and steady‐state efficiencies of up to 22.0% during maximum power point tracking. Thanks to its low lateral conductivity, the nanocrystalline silicon recombination junction enables upscaling of monolithic perovskite/silicon heterojunction tandem cells, resulting in a 12.96 cm2 monolithic tandem cell with a steady‐state efficiency of 18%.
A nanocrystalline silicon recombination junction is presented, which mitigates reflection losses in monolithic perovskite/silicon heterojunction tandem solar cells, resulting in efficiencies of up to 22.7% on an aperture area of 0.25 cm2. Thanks to its low lateral conductance, this recombination junction enables tandem cell up‐scaling, leading to a steady‐state efficiency of 18% on an aperture area of 12.96 cm2.
Transition metal oxides (TMOs) are commonly used in a wide spectrum of device applications, thanks to their interesting electronic, photochromic, and electrochromic properties. Their environmental ...sensitivity, exploited for gas and chemical sensors, is however undesirable for application in optoelectronic devices, where TMOs are used as charge injection or extraction layers. In this work, we first study the coloration of molybdenum and tungsten oxide layers, induced by thermal annealing, Ar plasma exposure, or transparent conducting oxide overlayer deposition, typically used in solar cell fabrication. We then propose a discoloration method based on an oxidizing CO2 plasma treatment, which allows for a complete bleaching of colored TMO films and prevents any subsequent recoloration during following cell processing steps. Then, we show that tungsten oxide is intrinsically more resilient to damage induced by Ar plasma exposure as compared to the commonly used molybdenum oxide. Finally, we show that parasitic absorption in TMO-based transparent electrodes, as used for semitransparent perovskite solar cells, silicon heterojunction solar cells, or perovskite/silicon tandem solar cells, can be drastically reduced by replacing molybdenum oxide with tungsten oxide and by applying a CO2 plasma pretreatment prior to the transparent conductive oxide overlayer deposition.
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