ZiQi Sun

Despite recent breakthroughs in power conversion efficiencies (PCEs), which have resulted in PCEs exceeding 22%, perovskite solar cells (PSCs) still face serious drawbacks in terms of their printability, reliability, and stability. The most efficient PSC architecture, which is based on titanium dioxide as an electron transport layer, requires an extremely high-temperature sintering process (≈500 °C), reveals hysterical discrepancies in the device measurement, and suffers from performance degradation under light illumination. These drawbacks hamper the practical development of PSCs fabricated via a printing process on flexible plastic substrates. Herein, an innovative method to fabricate low-temperature-processed, hysteresis-free, and stable PSCs with a large area up to 1 cm² is demonstrated using a versatile organic nanocomposite that combines an electron acceptor and a surface modifier. This nanocomposite forms an ideal, self-organized electron transport layer (ETL) via a spontaneous vertical phase separation, which leads to hysteresis-free, planar heterojunction PSCs with stabilized PCEs of over 18%. In addition, the organic nanocomposite concept is successfully applied to the printing process, resulting in a PCE of over 17% in PSCs with printed ETLs.

An innovative method for achieving printable planar heterojunction perovskite solar cells (PSCs) is demonstrated using self-assembled organic nanocomposites of fullerene derivatives and cationic polyelectrolytes as the electron transport layer. Highly reliable and stable PSCs with low-temperature solution-processable organic nanocomposites exhibit stabilized power conversion efficiencies exceeding 18%.

An organic–inorganic integrated hole transport layer (HTL) composed of the solution-processable nickel phthalocyanine (NiPc) abbreviated NiPc-(OBu)₈ and vanadium(V) oxide (V₂O₅) is successfully incorporated into structured mesoporous perovskite solar cells (PSCs). The optimized PSCs show the highest stabilized power conversion efficiency of up to 16.8% and good stability under dark ambient conditions. These results highlight the potential application of organic–inorganic integrated HTLs in PSCs.

A perovskite solar cell containing a NiPc-(OBu)₈ and V₂O₅ based organic–inorganic integrated hole transport layer is reported. It achieves a power conversion efficiency of 17.6%.

In recent years, Cu₂ZnSn(S,Se)₄ (CZTSSe) materials have enabled important progress in associated thin-film photovoltaic (PV) technology, while avoiding scarce and/or toxic metals; however, cationic disorder and associated band tailing fundamentally limit device performance. Cu₂BaSnS₄ (CBTS) has recently been proposed as a prospective alternative large bandgap (~2 eV), environmentally friendly PV material, with ~2% power conversion efficiency (PCE) already demonstrated in corresponding devices. In this study, a two-step process (i.e., precursor sputter deposition followed by successive sulfurization/selenization) yields high-quality nominally pinhole-free films with large (>1 µm) grains of selenium-incorporated (x = 3) Cu₂BaSnS_4−xSe_x (CBTSSe) for high-efficiency PV devices. By incorporating Se in the sulfide film, absorber layers with 1.55 eV bandgap, ideal for single-junction PV, have been achieved within the CBTSSe trigonal structural family. The abrupt transition in quantum efficiency data for wavelengths above the absorption edge, coupled with a strong sharp photoluminescence feature, confirms the relative absence of band tailing in CBTSSe compared to CZTSSe. For the first time, by combining bandgap tuning with an air-annealing step, a CBTSSe-based PV device with 5.2% PCE (total area 0.425 cm²) is reported, >2.5× better than the previous champion pure sulfide device. These results suggest substantial promise for the emerging Se-rich Cu₂BaSnS_4–xSe_x family for high-efficiency and earth-abundant PV.

By incorporating Se in a pure sulfide film, earth-abundant Cu₂BaSnS_4−xSe_x (x = 3) films with 1.55 eV bandgap, a near-perfect match for single-junction photovoltaic (PV) devices operating under AM 1.5G solar radiation, are successfully achieved. Sharp cut-offs in the external quantum efficiency data and photoluminescence features confirm the relative absence of band tailing in the Cu₂BaSnS_4−xSe_x system. A Cu₂BaSnS_4−xSe_x-based PV device with total area 0.425 cm² exhibits a power conversion efficiency of 5.2%.

Organic–inorganic perovskites with intriguing optical and electrical properties have attracted significant research interests due to their excellent performance in optoelectronic devices. Recent efforts on preparing uniform and large-grain polycrystalline perovskite films have led to enhanced carrier lifetime up to several microseconds. However, the mobility and trap densities of polycrystalline perovskite films are still significantly behind their single-crystal counterparts. Here, a facile topotactic-oriented attachment (TOA) process to grow highly oriented perovskite films, featuring strong uniaxial-crystallographic texture, micrometer-grain morphology, high crystallinity, low trap density (≈4 × 10¹⁴ cm⁻³), and unprecedented 9 GHz charge-carrier mobility (71 cm² V⁻¹ s⁻¹), is demonstrated. TOA-perovskite-based n-i-p planar solar cells show minimal discrepancies between stabilized efficiency (19.0%) and reverse-scan efficiency (19.7%). The TOA process is also applicable for growing other state-of-the-art perovskite alloys, including triple-cation and mixed-halide perovskites.

A facile topotactic-oriented attachment process can produce uniaxially oriented perovskite thin films with micrometer-grain morphology, high crystallinity, low trap density (≈4 × 10¹⁴ cm⁻³), and fast 9 GHz charge-carrier mobility (71 cm² V⁻¹ s⁻¹). The n-i-p planar perovskite solar cell exhibits a power conversion efficiency of 19.7% (with stabilized efficiency output of 19.0%).

Minimization of defects in absorber materials is essential for hybrid perovskite solar cells, especially when constructing thick polycrystalline layers in a planar configuration. Here, a simple methylamine solution-based additive is reported to improve film quality with nearly an order of magnitude reduction in intrinsic defect concentration. In the resultant film, an increase in carrier lifetime as a result of a decrease in shallow electronic disorder is observed. This superior crystalline film quality is further evidenced via a doubled spin relaxation time as compared with other reports. Bearing sufficient carrier diffusion length, a thick absorber layer (≈650 nm) is implemented in planar devices to achieve a champion power conversion efficiency of 20.02% with a stabilized output efficiency of 19.01% under one sun illumination. This work demonstrates a simple approach to improve hybrid perovskite film quality by substantial reduction of intrinsic defects for wide applications in optoelectronics.

A simple methylamine solution-based additive to improve film quality with nearly an order of magnitude reduction in the concentration of intrinsic defects is reported, and the relevant perovskite solar cells achieve a champion power conversion efficiency of 20.02% with a stabilized output efficiency of 19.01% under 1 sun illumination.

Tin (Sn)-based perovskites are increasingly attractive because they offer lead-free alternatives in perovskite solar cells. However, depositing high-quality Sn-based perovskite films is still a challenge, particularly for low-temperature planar heterojunction (PHJ) devices. Here, a “multichannel interdiffusion” protocol is demonstrated by annealing stacked layers of aqueous solution deposited formamidinium iodide (FAI)/polymer layer followed with an evaporated SnI₂ layer to create uniform FASnI₃ films. In this protocol, tiny FAI crystals, significantly inhibited by the introduced polymer, can offer multiple interdiffusion pathways for complete reaction with SnI₂. What is more, water, rather than traditional aprotic organic solvents, is used to dissolve the precursors. The best-performing FASnI₃ PHJ solar cell assembled by this protocol exhibits a power conversion efficiency (PCE) of 3.98%. In addition, a flexible FASnI₃-based flexible solar cell assembled on a polyethylene naphthalate–indium tin oxide flexible substrate with a PCE of 3.12% is demonstrated. This novel interdiffusion process can help to further boost the performance of lead-free Sn-based perovskites.

Flexible lead-free perovskite solar cells are achieved using FASnI₃ via a novel water-based multichannel interdiffusion protocol for the first time. Nanosized formamidinium iodide crystals inhibited by the introduced polymer of the aqueous salt/polymer solutions provide multiple channels to completely react with evaporated SnI₂. The highest power conversion efficiency of 3.98% and 3.12% is realized for rigid and flexible substrate, respectively.

Despite the recent unprecedented increase in the power conversion efficiencies (PCEs) of small-area devices (≤0.1 cm²), the PCEs deteriorate drastically for PSCs of larger areas because of the incomplete film coverage caused by the dewetting of the hydrophilic perovskite precursor solutions on the hydrophobic organic charge-transport layers (CTLs). Here, an innovative method of fabricating scalable PSCs on all types of organic CTLs is reported. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, fabricating uniform perovskite films on large-area substrates (18.4 cm²) and PSCs with the total active area of 6 cm² (1 cm² × 6 unit cells) via a single-turn solution process is successfully demonstrated. All of the unit cells exhibit highly uniform PCEs of 16.1 ± 0.9% (best PCE of 17%), which is the highest value for printable PSCs with a total active area larger than 1 cm².

Large-area planar perovskite solar cells (PSCs) are demonstrated by an innovative method using an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer between the hydrophobic organic charge-transport layer and hydrophilic perovskite layer. Highly scalable PSCs with uniform perovskite films on a large-area substrate (18.4 cm²) and with an active area of 1 cm² exhibit stabilized power conversion efficiencies of 17%.