Improvements to perovskite solar cells (PSCs) have focused on increasing their power conversion efficiency (PCE) and operational stability and maintaining high performance upon scale-up to module sizes. We report that replacing the commonly used mesoporous–titanium dioxide electron transport layer (ETL) with a thin layer of polyacrylic acid–stabilized tin(IV) oxide quantum dots (paa-QD-SnO2) on the compact–titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL–perovskite interface. The use of paa-QD-SnO2 as electron-selective contact enabled PSCs (0.08 square centimeters) with a PCE of 25.7% (certified 25.4%) and high operational stability and facilitated the scale-up of the PSCs to larger areas. PCEs of 23.3, 21.7, and 20.6% were achieved for PSCs with active areas of 1, 20, and 64 square centimeters, respectively. Description Tailoring tin oxide layers Mesoporous titanium dioxide is commonly used as the electron transport layer in perovskite solar cells, but electron transport layers based on tin(IV) oxide quantum dots could be more efficient, with a better-aligned conduction band and a higher carrier mobility. Kim et al. show that such quantum dots could conformally coat a textured fluorine-doped tin oxide electrode when stabilized with polyacrylic acid. Improved light trapping and reduced nonradiative recombination resulted in a certified power conversion efficiency of 25.4% and high operational stability. In larger-area minimodules, active areas as high as 64 square centimeters maintained certified power conversion efficiencies of more than 20%. —PDS Polymer-stabilized tin oxide nanoparticles suppress recombination at the electron-transport layer–perovskite interface.

Conformal quantum dot–SnO2 layers as electron transporters for efficient perovskite solar cells

Further enhancing the performance and stability of inverted perovskite solar cells (PSCs) is crucial for their commercialization. We report that the functionalization of multication and halide perovskite interfaces with an organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate (FcTc2), simultaneously enhanced the efficiency and stability of inverted PSCs. The resultant devices achieved a power conversion efficiency of 25.0% and maintained >98% of their initial efficiency after continuously operating at the maximum power point for 1500 hours under simulated AM1.5 illumination. Moreover, the FcTc2-functionalized devices passed the international standards for mature photovoltaics (IEC61215:2016) and have exhibited high stability under the damp heat test (85°C and 85% relative humidity). Description Organometallics stabilizing perovskites Perovskite solar cells with inverted (p-i-n) structure can have greater stability and lifetimes than conventional n-i-p structures but usually have somewhat lower power conversion efficiencies (PCEs). Li et al. report that an organometallic compound, ferrocenyl-bis-thiophene-2-carboxylate, can stabilize a multication perovskite layer of an inverted perovskite solar cells. After 1500 hours of maximum power point operation, 98% of the 25.0% PCE was maintained. The solar cell also exhibited high stability in damp heat tests. —PDS Functionalizing interfaces with an organometallic compound created an efficient and stable inverted perovskite solar cell.

Organometallic-functionalized interfaces for highly efficient inverted perovskite solar cells

If perovskite solar cells (PSCs) with high power conversion efficiencies (PCEs) are to be commercialized, they must achieve long-term stability, which is usually assessed with accelerated degradation tests. One of the persistent obstacles for PSCs has been successfully passing the damp-heat test (85°C and 85% relative humidity), which is the standard for verifying the stability of commercial photovoltaic (PV) modules. We fabricated damp heat–stable PSCs by tailoring the dimensional fragments of two-dimensional perovskite layers formed at room temperature with oleylammonium iodide molecules; these layers passivate the perovskite surface at the electron-selective contact. The resulting inverted PSCs deliver a 24.3% PCE and retain >95% of their initial value after >1000 hours at damp-heat test conditions, thereby meeting one of the critical industrial stability standards for PV modules. Description Stabilizing inverted solar cells Although inverted (p-i-n) perovskite solar cells (PSCs) have advantages in fabrication and scaling compared with n-i-p cells, their power conversion efficiencies (PCEs ) are usually lower. Azmi et al. show that by tailoring the number of octahedral inorganic sheets in two-dimensional perovskite (2DP) passivation layers for three-dimensional perovskite active layers, PCEs of more than 24% could be achieved (see the Perspective by Luther and Schelhas). The 2DP layers formed with oleylammonium iodide molecules at the electron-selective interface passivated trap states and suppressed ion migration. These PSCs retained more than 95% of their initial efficiency after 1000 hours of damp-heat testing (85°C and 85% relative humidity), which passes a key industrial stability standard. —PDS Tailored two-dimensional perovskite passivation layers enable efficient, damp-heat stable inverted perovskite solar cells.

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Damp heat–stable perovskite solar cells with tailored-dimensionality 2D/3D heterojunctions

Origins and influences of metallic lead in perovskite solar cells

Reducing the electronic defects in perovskite films has become a substantial challenge to further boost the photovoltaic performance of perovskite solar cells. Here, 2D (NpMA)2PbI4 perovskite and 1‐naphthalenemethylammonium iodide (NpMAI) are separately introduced into the PbI2 precursor solutions to regulate the crystal growth in a 2D/3D perovskite film using a two‐step deposition method. The (NpMA)2PbI4 modulated perovskite film shows a significantly improved film quality with enlarged grain size from ≈500 nm to over 1000 nm, which greatly reduces the grain‐boundary defects, improves the charge carrier lifetime, and hinders ionic diffusion. As a result, the best‐performing device shows a high power conversion efficiency (PCE) of 24.37% for a small‐area (0.10 cm−2) device and a superior PCE of 22.26% for a large‐area (1.01 cm−2) device. Importantly, the unencapsulated device shows a dramatically improved operational stability with maintains over 98% of its initial efficiency after 1500 h by maximum power point (MPP) tracking under continuous light irradiation.

Crystal Growth Regulation of 2D/3D Perovskite Films for Solar Cells with Both High Efficiency and Stability

Metal halide perovskite solar cells have demonstrated a high power conversion efficiency (PCE), and further enhancement of the PCE requires a reduction of the bandgap-voltage offset (WOC) and the non-radiative recombination photovoltage loss (ΔVOC,nr). Here, we report an effective approach for reducing the photovoltage loss through the simultaneous passivation of internal bulk defects and dimensionally graded two-dimensional perovskite interface defects. Through this dimensionally graded perovskite formation approach, an open-circuit voltage (VOC) of 1.24 V was obtained with a champion PCE of 21.54% in a 1.63 eV perovskite system (maximum VOC = 1.25 V, WOC = 0.38 V and ΔVOC,nr = 0.10 V); we further decreased the WOC to 0.326 V in a 1.53 eV perovskite system with a VOC of 1.21 V and a PCE of 23.78% (certified 23.09%). This approach is equally effective in achieving a low WOC (ΔVOC,nr) in 1.56 eV and 1.73 eV perovskite solar cell systems, and further leads to the substantially improved operational stability of perovskite solar cells. The use of a dimensionally graded 2D perovskite interface and passivation results in perovskite solar cells with very low photovoltage loss.

Bowei Gao

Papers

Stable and low-photovoltage-loss perovskite solar cells by multifunctional passivation