Low-bandgap Perovskite Solar Cells Research Articles

Pure 2D Perovskite Formation by Interfacial Engineering Yields a High Open-Circuit Voltage beyond 1.28 V for 1.77-eV Wide-Bandgap Perovskite Solar Cells.

Surface post-treatment using ammonium halides effectively reduces large open-circuit voltage (VOC ) losses in bromine-rich wide-bandgap (WBG) perovskite solar cells (PSCs). However, the underlying mechanism still remains unclear and the device efficiency lags largely behind. Here, a facile strategy of precisely tailoring the phase purity of 2D perovskites on top of 3D WBG perovskite and realizing high device efficiency is reported. The transient absorption spectra, cross-sectional confocal photoluminescence mapping, and cross-sectional Kelvin probe force microscopy are combined to demonstrate optimal defect passivation effect and surface electric-field of pure n=1 2D perovskites formed atop 3D WBG perovskites via low-temperature annealing. As a result, the inverted champion device with 1.77-eV perovskite absorber achieves a high VOC of 1.284V and a power conversion efficiency (PCE) of 17.72%, delivering the smallest VOC deficit of 0.486V among WBG PSCs with a bandgap higher than 1.75eV. This enables one to achieve a four-terminal all-perovskite tandem solar cell with a PCE exceeding 25% by combining with a 1.25-eV low-bandgap PSC.

Efficient MA-free Pb-Sn alloyed low-bandgap perovskite solar cells via surface passivation

Lead-tin (Pb-Sn) alloyed low-bandgap perovskite solar cell (PSC) is the critical component of all-perovskite tandem solar cells. Although there is a clear trend of avoiding volatile methylammonium (MA) cations in the state-of-the-art lead-halide PSCs, the high-efficiency Pb-Sn mixed PSCs (with efficiencies over 20%) are still generally containing over 30 mol% MA cations making their thermal and operational stabilities very questionable. Here, our experiments show that the PSC based on MA-free FA0.83Cs0.17Pb0.5Sn0.5I3 composition has the T80 20 times longer than that of MA-containing FA0.6MA0.4Pb0.6Sn0.4I3 based device, but a lower efficiency of 17.71% versus 20.45% (T80 refers as the efficiency decrease to 80% of the initial value upon continuous one-sun illumination). Thus, it is greatly necessary to develop high-efficiency MA-free Pb-Sn mixed PSCs. Herein, we developed a facile post-treated method to enhance the efficiency of MA-free FA0.83Cs0.17Pb0.5Sn0.5I3 PSCs. By growing an ultrathin layer of phenethylammonium iodide (PEAI) on top of FA0.83Cs0.17Pb0.5Sn0.5I3 film, it not only passivated the film surface detects but also suppressed the Sn2+ oxidation evidenced by the improved charge carrier lifetime from 540 ns to 682 ns and a reduced amount of Sn4+ species. In addition, the thin layer of PEAI also modified the junction quality at the perovkite/C60 interface leading to more efficient electron transportation. Finally, the PEAI-treated PSCs delivered an improved open-circuit voltage (Voc) of 0.795 V and efficiency of 19.12% versus 0.766 V and 17.72% for the control device. We hope this work could shed more light on the further progress of MA-free Pb-Sn mixed PSCs.

Back Interface Passivation for Efficient Low-Bandgap Perovskite Solar Cells and Photodetectors.

Low-bandgap (Eg~1.25 eV) mixed tin-lead (Sn-Pb) perovskites are promising candidates for efficient solar cells and self-powered photodetectors; however, they suffer from huge amounts of defects due to the unintentional p-type self-doping. In this work, the synergistic effects of maltol and phenyl-C61-butyric acid methyl ester (PCBM) were achieved to improve the performance of low-bandgap perovskite solar cells (PSCs) and unbiased perovskite photodetectors (PPDs) by passivating the defects and tuning charge transfer dynamics. Maltol eliminated the Sn-related traps in perovskite films through a strong metal chelating effect, whereas PCBM elevated the built-in electric potential and thus improved voltage through the spike energy alignment. Combining both advantages of maltol and PCBM, high-quality perovskite films were obtained, enabling low-bandgap PSCs with the best efficiency of 20.62%. Moreover, the optimized PSCs were further applied as self-powered PPDs in a visible light communication system with a response time of 0.736 μs, presenting a satisfactory audio transmission capability.

Methylammonium and Bromide‐Free Tin‐Based Low Bandgap Perovskite Solar Cells

AbstractLead halide‐based perovskite solar cells (PSCs) are intriguing candidates for photovoltaic technology because of their high efficiency, low cost, and simple process advantages. Owing to lead toxicity, PSCs based on partially/fully substituted Pb with tin have attracted tremendous attention, which would enable the ideal bandgap to approach the Shockley‐Queisser (S‐Q) limit. Especially, methylammonium (MA), bromide‐free, tin‐based perovskites are striking, because of the intrinsic poor stability of MA and blue shift caused by the incorporation of Br−. The first section of this review emphasizes the motivation for studying single‐junction MA, Br‐free, and Sn‐based perovskites. The film quality improvement strategies of Sn‐based perovskites, including additive, composition, dimensional, and interface engineering toward high‐efficiency devices are comprehensively overviewed. Moreover, strategies to improve stability, where shelf, thermal and operational stabilities of the devices are summarized. Finally, this review concludes with a discussion of actual limitations and future prospects for Sn‐based PSCs.

Designed p-type graphene quantum dots to heal interface charge transfer in Sn-Pb perovskite solar cells

In Sn-Pb based low bandgap perovskite solar cells (LB-PSCs), the large energy loss of ~0.5 eV lags its development, originating from unfavorable band alignment at the interface and serious charge recombination in the device. Here, judiciously designed graphene quantum dots by functional N/Cl doping are applied at PEDOT:PSS/perovskite interface to modulate the energy level and charge transfer simultaneously. Among three designed graphene quantum dots, the N, Cl codoped one (N,Cl-GQDs) induces the best band alignment, because of the enhanced p-doping. Besides, N,Cl-GQDs best regulate the charge distribution and passivate the defect states at the interface by π-conjugated effect and electronegative Cl, paving the way for efficient interface charge transport. Upon N,Cl-GQDs optimization, the FA0.6MA0.4Sn0.6Pb0.4I3 based PSCs achieves impressive efficiency of 21.5% (1 sun, AM1.5) with a high photovoltage of ~0.89 V (energy loss of ~0.36 eV) and fill factor over 80%, which are among the best parameters in reported LB-PSCs. The N,Cl-GQDs modified device exhibits the best shelf stability after 1000 h, due to the least trap states and reformative interface. This work highlights designed graphene quantum dots for photovoltaic applications.

Interface Engineering of Pb–Sn Low‐Bandgap Perovskite Solar Cells for Improved Efficiency and Stability

Because of their inferior film quality, Pb–Sn‐mixed low‐bandgap (LBG) perovskites suffer from poor charge transportation, compromising photovoltaic parameters of final solar cells. Herein, an approach to improve the quality of the charge interface layer is proposed, in which a thin layer of hydrophobic [bis (4‐phenyl) (2, 4, 6‐trimethylphenyl) amine] (PTAA) is inserted between the hole‐selective layer of hydrophilic poly (3, 4‐ethylenedioxythiophene) ‐polystyrenesulfonicacid (PEDOT:PSS) and LBG perovskite layer. The introduction of a tiny layer of the hydrophobic PTAA acts as a shield layer to protect the underlying acidic PEDOT:PSS layer from moisture‐related degradation and works as an intermediary layer to facilitate the growth of significantly larger perovskite grains; these enlarged grains are indicative of enhanced crystallinity and fewer grain boundaries in the perovskite layer. The fewer grain boundaries lead to suppression of interfacial defects and result in enhanced charge collection at the hole transport layer/perovskite interface, thus improving the open‐circuit voltage up to 0.85 V and fill factor up to ≈78%, eventually boosting the power conversion efficiency of the champion cell up to 19.08%. Herein, a simple interface engineering route to fabricate efficient and stable Pb–Sn‐mixed LBG perovskite solar cells is offered.

Preventing inhomogeneous elemental distribution and phase segregation in mixed Pb-Sn inorganic perovskites via incorporating PbS quantum dots

Inhomogeneous Pb/Sn elemental distribution and the resulted phase segregation in mixed Pb-Sn halide perovskites would result in energy disorder (band structure and phase distribution disorder), which greatly limits their photovoltaic performance. Here, PbS quantum dot has been synthesized and demonstrated as seeds for modulation crystallization dynamics of the mixed Pb-Sn inorganic perovskites, allowing an enhanced film quality and significantly suppressing phase segregation. With this additive power conversion efficiency of 8% and 6% is obtained under irradiation of full sunlight in planar and mesoporous structured solar cells in combination with CsPb0.5Sn0.5I2Br inorganic perovskite, respectively. Our finding reveals exploring the actual Pb/Sn atoms location in perovskite structure and its influence on developing efficient and stable low-bandgap perovskite solar cells.

Mitigating Open-Circuit Voltage Loss in Pb–Sn Low-Bandgap Perovskite Solar Cells via Additive Engineering

Lead (Pb)–Tin (Sn) mixed perovskites suffer from large open-circuit voltage (Voc) loss due to the rapid crystallization of perovskite films, creating Sn and Pb vacancies. Such vacancies act as defect sites expediting charge carrier recombination, thus hampering the charge carrier dynamics and optoelectronic properties of the perovskite film. Here, we report the passivation of these defects using a controlled amount of 2-phenylethylazanium iodide (PEAI) in perovskite precursor solution as a dopant to enhance the performance of the 1.25 eV Pb–Sn low-bandgap perovskite solar cell. It was found that the incorporation of PEAI in the perovskite precursor not only improves the perovskite film quality and crystallinity but also lowers the electronic disorder, thereby enhancing the open-circuit voltage up to 0.85 V, corresponding to Voc loss as low as 0.4 V and the power conversion efficiency up to 17.33%. The value of Voc loss obtained with this strategy is among the least obtained for similar band gap Pb–Sn low-bandgap perovskite solar cells. Furthermore, the ambient and dark self-stability of the PEAI-treated devices were also enhanced. This work presents a simple doping strategy to mitigate the Voc loss of Pb–Sn mixed low-bandgap perovskite solar cells.

Low-bandgap mixed tin–lead iodide perovskites with reduced methylammonium for simultaneous enhancement of solar cell efficiency and stability

High-performance perovskite/perovskite tandem solar cells require high-efficiency and stable low-bandgap perovskite subcells. State-of-the-art low-bandgap mixed tin–lead iodide perovskite solar cells exhibit either a high power-conversion efficiency or improved stability, but not both. Here we report a two-step bilayer interdiffusion growth process to simultaneously meet both requirements for formamidinium-based low-bandgap mixed tin–lead iodide perovskite solar cells. The bilayer interdiffusion growth process allows for the formation of high-quality and large-grained perovskite films with only 10 mol% volatile methylammonium. Additionally, one-dimensional pyrrolidinium perovskite was applied to passivate the perovskite film and improve the junction quality, which resulted in a carrier lifetime of 1.1 μs and an open circuit voltage of 0.865 V for our perovskite film and device with a bandgap of 1.28 eV. Our strategies enabled a power-conversion efficiency of 20.4% for low-bandgap perovskite solar cells under AM 1.5G illumination. More importantly, an encapsulated device can retain 92% of its initial efficiency after 450 h of continuous 1 sun illumination. Low-bandgap tin–lead perovskites are key to all-perovskite tandem solar cells but simultaneous improvement in efficiency and stability has proven challenging. Now, Li et al. fabricate tin–lead perovskite cells with reduced methylammonium content that are 20.4% efficient and stable under illumination for 450 h.

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

Incorporating 2.5% Cs in FA0.8MA0.2Sn0.5Pb0.5I3 improves the photo-stability of the low-bandgap perovskite solar cells. The champion device with power conversion efficiency of 18.9% maintain 92% of its initial efficiency after 120 min MPP tracking.

Monolithic all-perovskite tandem solar cells with 24.8% efficiency exploiting comproportionation to suppress Sn(ii) oxidation in precursor ink

Combining wide-bandgap and narrow-bandgap perovskites to construct monolithic all-perovskite tandem solar cells offers avenues for continued increases in photovoltaic (PV) power conversion efficiencies (PCEs). However, actual efficiencies today are diminished by the subpar performance of narrow-bandgap subcells. Here we report a strategy to reduce Sn vacancies in mixed Pb–Sn narrow-bandgap perovskites that use metallic tin to reduce the Sn4+ (an oxidation product of Sn2+) to Sn2+ via a comproportionation reaction. We increase, thereby, the charge-carrier diffusion length in narrow-bandgap perovskites to 3 μm for the best materials. We obtain a PCE of 21.1% for 1.22-eV narrow-bandgap solar cells. We fabricate monolithic all-perovskite tandem cells with certified PCEs of 24.8% for small-area devices (0.049 cm2) and of 22.1% for large-area devices (1.05 cm2). The tandem cells retain 90% of their performance following 463 h of operation at the maximum power point under full 1-sun illumination. Improvements in the efficiency and stability of low-bandgap perovskite solar cells are key to enabling all-perovskite solar cells. Here, Lin et al. use metallic tin to prevent oxidation in such low-gap perovskite and demonstrate 24.8%-efficient tandems that are stable for over 400 h under operating conditions.

Low-temperature processed inorganic hole transport layer for efficient and stable mixed Pb-Sn low-bandgap perovskite solar cells

Low-temperature processed inorganic hole transport layer for efficient and stable mixed Pb-Sn low-bandgap perovskite solar cells

A cascade-type electron extraction design for efficient low-bandgap perovskite solar cells based on a conventional structure with suppressed open-circuit voltage loss

A cascade-type and energy-level-aligned electron transport layer of ZnO/SnO2/C60-SAM is beneficial for suppressed charge recombination and improved charge extraction in low-bandgap perovskite solar cells, resulting in a reduced Voc loss.

Efficient two-terminal all-perovskite tandem solar cells enabled by high-quality low-bandgap absorber layers

Multi-junction all-perovskite tandem solar cells are a promising choice for next-generation solar cells with high efficiency and low fabrication cost. However, the lack of high-quality low-bandgap perovskite absorber layers seriously hampers the development of efficient and stable two-terminal monolithic all-perovskite tandem solar cells. Here, we report a bulk-passivation strategy via incorporation of chlorine, to enlarge grains and reduce electronic disorder in mixed tin–lead low-bandgap (~1.25 eV) perovskite absorber layers. This enables the fabrication of efficient low-bandgap perovskite solar cells using thick absorber layers (~750 nm), which is a requisite for efficient tandem solar cells. Such improvement enables the fabrication of two-terminal all-perovskite tandem solar cells with a champion power conversion efficiency of 21% and steady-state efficiency of 20.7%. The efficiency is retained to 85% of its initial performance after 80 h of operation under continuous illumination. Two-terminal monolithic all-perovskite tandem solar cells are attractive due to their flexible nature and low-cost fabrication. Here the authors develop a process to obtain high-quality Sn–Pb perovskite thin films by incorporating chlorine. Such layers are employed to fabricate 20.7%-efficient tandem cells with 80 h operational stability.

High performance low-bandgap perovskite solar cells based on a high-quality mixed Sn–Pb perovskite film prepared by vacuum-assisted thermal annealing

Vacuum-assisted thermal annealing not only could improve film morphology and crystallinity, but also could accelerate the sublimation of undesired MACl. With the help of this process, we obtain a highly efficient low-bandgap CH3NH3Sn0.5Pb0.5IxCl3−x perovskite solar cell with a power conversion efficiency of 12.3%.

Low-bandgap mixed tin–lead iodide perovskite absorbers with long carrier lifetimes for all-perovskite tandem solar cells

Tandem solar cells using only metal-halide perovskite sub-cells are an attractive choice for next-generation solar cells. However, the progress in developing efficient all-perovskite tandem solar cells has been hindered by the lack of high-performance low-bandgap perovskite solar cells. Here, we report efficient mixed tin–lead iodide low-bandgap (∼1.25 eV) perovskite solar cells with open-circuit voltages up to 0.85 V and over 70% external quantum efficiencies in the infrared wavelength range of 700–900 nm, delivering a short-circuit current density of over 29 mA cm−2 and demonstrating suitability for bottom-cell applications in all-perovskite tandem solar cells. Our low-bandgap perovskite solar cells achieve a maximum power conversion efficiency of 17.6% and a certified efficiency of 17.01% with a negligible current–voltage hysteresis. When mechanically stacked with a ∼1.58 eV bandgap perovskite top cell, our best all-perovskite 4-terminal tandem solar cell shows a steady-state efficiency of 21.0%. All-perovskite tandem solar cells hold the promise of high efficiencies whilst safeguarding the ease of fabrication intrinsic to perovskites. Here, Zhao et al. present a certified 17% efficient tin and lead perovskite solar cell, which is integrated as the low-bandgap component of a tandem device with 21% efficiency.

Fabrication of Efficient Low-Bandgap Perovskite Solar Cells by Combining Formamidinium Tin Iodide with Methylammonium Lead Iodide.

Mixed tin (Sn)-lead (Pb) perovskites with high Sn content exhibit low bandgaps suitable for fabricating the bottom cell of perovskite-based tandem solar cells. In this work, we report on the fabrication of efficient mixed Sn-Pb perovskite solar cells using precursors combining formamidinium tin iodide (FASnI3) and methylammonium lead iodide (MAPbI3). The best-performing cell fabricated using a (FASnI3)0.6(MAPbI3)0.4 absorber with an absorption edge of ∼1.2 eV achieved a power conversion efficiency (PCE) of 15.08 (15.00)% with an open-circuit voltage of 0.795 (0.799) V, a short-circuit current density of 26.86(26.82) mA/cm(2), and a fill factor of 70.6(70.0)% when measured under forward (reverse) voltage scan. The average PCE of 50 cells we have fabricated is 14.39 ± 0.33%, indicating good reproducibility.