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All-perovskite tandem solar cells provide high power conversion efficiency at a low cost 1 – 4 . Rapid efficiency improvement in small-area (<0.1 cm 2 ) tandem solar cells has been primarily driven by advances in low-bandgap (approximately 1.25 eV) perovskite bottom subcells 5 – 7 . However, unsolved issues remain for wide-bandgap (> 1.75 eV) perovskite top subcells 8 , which at present have large voltage and fill factor losses, particularly for large-area (>1 cm 2 ) tandem solar cells. Here we develop a self-assembled monolayer of (4-(7 H -dibenzo[ c,g ]carbazol-7-yl)butyl)phosphonic acid as a hole-selective layer for wide-bandgap perovskite solar cells, which facilitates subsequent growth of high-quality wide-bandgap perovskite over a large area with suppressed interfacial non-radiative recombination, enabling efficient hole extraction. By integrating (4-(7 H -dibenzo[ c,g ]carbazol-7-yl)butyl)phosphonic acid in devices, we demonstrate a high open-circuit voltage ( V OC ) of 1.31 V in a 1.77-eV perovskite solar cell, corresponding to a very low V OC deficit of 0.46 V (with respect to the bandgap). With these wide-bandgap perovskite subcells, we report 27.0% (26.4% certified stabilized) monolithic all-perovskite tandem solar cells with an aperture area of 1.044 cm 2 . The certified tandem cell shows an outstanding combination of a high V OC of 2.12 V and a fill factor of 82.6%. Our demonstration of the large-area tandem solar cells with high certified efficiency is a key step towards scaling up all-perovskite tandem photovoltaic technology. A self-assembled monolayer of (4-(7 H -dibenzo[ c,g ]carbazol-7-yl)butyl)phosphonic acid is integrated in wide-bandgap perovskite solar cells, which enables a high power conversion efficiency and low open-circuit voltage deficiency, as well as efficient centimetre-scale all-perovskite tandem solar cells.

Perovskite–silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.Designing gentle sinusoidal nanotextures enables the realization of high-efficiency perovskite–silicon solar cells

Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C 60 interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C 60 interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. Effective transport layers are essential to suppress non-radiative recombination losses. Here, the authors introduce phenylamino-functionalized ortho-carborane as an interfacial layer, and realise inverted perovskite solar cells with efficiency of over 23% and operational stability of T97 = 400 h.

The performance of perovskite solar cells is predominantly limited by non-radiative recombination, either through trap-assisted recombination in the absorber layer or via minority carrier recombination at the perovskite/transport layer interfaces. Here, we use transient and absolute photoluminescence imaging to visualize all non-radiative recombination pathways in planar pin - type perovskite solar cells with undoped organic charge transport layers. We find significant quasi-Fermi-level splitting losses (135 meV) in the perovskite bulk, whereas interfacial recombination results in an additional free energy loss of 80 meV at each individual interface, which limits the open-circuit voltage ( V OC ) of the complete cell to ~1.12 V. Inserting ultrathin interlayers between the perovskite and transport layers leads to a substantial reduction of these interfacial losses at both the p and n contacts. Using this knowledge and approach, we demonstrate reproducible dopant-free 1 cm 2 perovskite solar cells surpassing 20% efficiency (19.83% certified) with stabilized power output, a high V OC (1.17 V) and record fill factor (>81%). Non-radiative recombination is a critical limiting factor for perovskite solar cell performance. Stolterfoht et al. visualize the various recombination pathways in planar pin cells with photoluminescence imaging and use it to design improved solar cells with 1 cm 2 areas and ~20% efficiency.

In this work, we couple theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (V OC ) and short-circuit current (J SC ) conditions. A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external V OC is detrimental for these devices. We demonstrate that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n -interface, suppressing the QFLS-V OC mismatch, and boosting the V OC . Concurrently, the use of an ionic interlayer or a self-assembled monolayer at the p -interface reduces the inferred field screening induced by mobile ions at J SC , promoting charge extraction and raising the J SC . The combination of the n- and p- type optimizations allows us to approach the thermodynamic potential of the perovskite absorber layer, resulting in 1 cm 2 devices with performance parameters of V OC s up to 1.29 V, fill factors above 80% and J SC s up to 17 mA/cm 2 , in addition to a thermal stability T 80  lifetime of more than 3500 h at 85 °C. A mismatch between quasi-Fermi level splitting and open-circuit voltage is detrimental to wide bandgap perovskite pin solar cells. Here, through theoretical and experimental approaches, the authors optimize n- and p-type interfaces to achieve open-circuit voltage of 1.29 V and T80 of 3500 h at 85 °C.

The efficiency of all-perovskite tandem solar cells has surpassed that of single-junction perovskite solar cells, yet they still suffer from interfacial non-radiative recombination losses. Charge-selective materials that can reduce such losses as well as fabrication cost “applicable” to both subcells should be developed. Here we design a donor–acceptor-type molecule, MPA2FPh-BT-BA (2F), as a hole-selective contact suitable to both wide-bandgap (WBG) and low-bandgap (LBG) subcells for high-performance all-perovskite tandem solar cells. In the WBG cell, 2F enables efficient hole extraction and minimizes interfacial non-radiative recombination losses by passivating interfacial defects. In the LBG cell, 2F suppresses interfacial losses, regulates the crystal growth and enhances Sn–Pb perovskite film quality. As a result, 2F-treated WBG and LBG devices yield efficiencies of 19.33% (certified 19.09%) and 23.24%, respectively, enabling monolithic all-perovskite tandem solar cells with an efficiency of 27.22% (certified 26.3%) and improved operational stability. Zhu et al. develop a low-cost donor–acceptor-type hole-selective layer that minimizes interfacial non-radiative charge recombination losses in single-junction and tandem solar cells based on metal halide perovskites with different bandgaps.

Blends of electron-donating and -accepting organic semiconductors are widely used as photoactive materials in next-generation solar cells and photodetectors. The yield of free charges in these systems is often determined by the separation of interfacial electron–hole pairs, which is expected to depend on the ability of the faster carrier to escape the Coulomb potential. Here we show, by measuring geminate and non-geminate losses and key transport parameters in a series of bulk-heterojunction solar cells, that the charge-generation yield increases with increasing slower carrier mobility. This is in direct contrast with the well-established Braun model where the dissociation rate is proportional to the mobility sum, and recent models that underscore the importance of fullerene aggregation for coherent electron propagation. The behaviour is attributed to the restriction of opposite charges to different phases, and to an entropic contribution that favours the joint separation of both charge carriers. In organic solar cells, the photogeneration of free charge carriers is limited by the dissociation of interfacial charge transfer states. Here, the authors study the impact of charge carrier mobilities in operational devices and show that the slowest charge carriers limit the dissociation of charge transfer states.

The rational design of perovskite heterojunctions is crucial for advancing the efficiency and operational stability of perovskite solar cells (PSCs). However, conventional methods face challenges in precisely controlling interfacial phase purity at the nanoscale and achieving conformal heterojunction coverage. Herein, we report a ‘soft-soft’ interaction-guided strategy to tailor perovskite heterojunction formation by introducing dimethyl sulfide (DMS) as a soft Lewis base additive in the organic cation solution. The resulting DMS-modulated PSCs achieve a remarkable power conversion efficiency (PCE) of up to 26.70%, with a certified PCE of 26.48%. The devices exhibit exceptional operational stability, retaining over 94% of their initial PCE after 2000 h of maximum power point tracking under continuous 1-sun illumination (ISOS-L-1 protocol). Furthermore, the universality of this ‘soft-soft’ interaction strategy is validated across a range of diverse perovskite compositions and ligand systems, demonstrating its potential for scalable and reproducible PSC fabrication. Conventional design of perovskite heterojunctions face challenges in precisely controlling interfacial phase purity at nanoscale. Here, the authors introduce dimethyl sulfide as a soft Lewis base additive in organic cation solution, achieving certified efficiency of 26.48% in stable solar cells.

Light harvesting systems based upon disordered materials are not only widespread innature, but are also increasingly prevalent in solar cells and photodetectors.Examples include organic semiconductors, which typically possess low charge carriermobilities and Langevin-type recombination dynamics – both of whichnegatively impact the device performance. It is accepted wisdom that the“drift distance” (i.e., the distance a photocarrier driftsbefore recombination) is defined by the mobility-lifetime product in solar cells. Wedemonstrate that this traditional figure of merit is inadequate for describing thecharge transport physics of organic light harvesting systems. It is experimentallyshown that the onset of the photocarrier recombination is determined by theelectrode charge and we propose the mobility-recombination coefficient product as analternative figure of merit. The implications of these findings are relevant to awide range of light harvesting systems and will necessitate a rethink of thecritical parameters of charge transport.

A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states.