Wenqiang Yang

Enhanced photovoltage for inverted planar heterojunction perovskite solar cells

Perovskite layers make the grade Inverted planar perovskite solar cells offer opportunities for a simplified device structure compared with conventional mesoporous titanium oxide interlayers. However, their lower open-circuit voltages result in lower power conversion efficiencies. Using mixed-cation lead mixed-halide perovskite and a solution-processed secondary growth method, Luo et al. created a surface region in the perovskite film that inhibited nonradiative charge-carrier recombination. This kind of solar cell had comparable performance to that of conventional cells. Science, this issue p. 1442 High open-circuit voltages were achieved for planar perovskite solar cells by creating a graded junction. The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (Voc). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts. We achieved a high Voc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

Pinhole-Free Hybrid Perovskite Film with Arbitrarily-Shaped Micro-Patterns for Functional Optoelectronic Devices

In many optoelectronic applications, patterning is required for functional and/or aesthetic purposes. However, established photolithographic technique cannot be applied directly to the hybrid perovskites, which are considered as promising candidates for optoelectronic applications. In this work, a wettability-assisted photolithography (WAP) process, which employs photolithography and one-step solution process to deposit hybrid perovskite, was developed for fabricating patterned hybrid perovskite films. Uniform pinhole-free hybrid perovskite films with sharp-edged micropatterns of any shapes can be constructed through the WAP process. Semitransparent solar cells with an adjustable active layer average visible transmittance of a wide range from 20.0% to 100% and regular solar cells based on patterned CH3NH3PbI3 perovskite films were fabricated to demonstrate that the WAP process was compatible with the manufacturing process of optoelectronic devices. With the widely equipped photolithographic facilities in the modern semiconductor industry, we believe the WAP process have a great potential in the industrial production of functionally or aesthetically patterned hybrid perovskite devices.

Fabrication of compact and stable perovskite films with optimized precursor composition in the fast-growing procedure

The fast-growing procedure (FGP) provides a simple, high-yield and lead (Pb)-release free method to prepare perovskite films. In the FGP, the ultra-dilute perovskite precursor solution is drop-cast onto a hot (~240°C) substrate, where a perovskite film grows immediately accompanied by the rapid evaporation of the host solvent. In this process, all the raw materials in the precursor solution are deposited into the final perovskite film. The potential pollution caused by Pb can be significantly reduced. Properties of the FGP-processed perovskite films can be modulated by the precursor composition. While CH3NH3Cl (MACl) affects the crystallization process and leads to full surface coverage, CH(NH2)2I (FAI) enhances the thermal stability of the film. Based on the optimized precursor composition of PbI2·(1−x)FAI·xMACl, x=0.75, FGP-processed planar heterojunction perovskite solar cells exhibit power conversion efficiencies (PCEs) exceeding 15% with suppressed hysteresis and excellent reproducibility.摘要快速成膜工艺提供了一种简单、高产率、无铅释放的钙钛矿薄膜制备方法. 在这一方法中, 低浓度的钙钛矿前驱体溶液被滴到240°C的热衬底上, 伴随着溶剂在高温条件下的迅速挥发, 钙钛矿在衬底表面迅速结晶, 生长成一层薄膜. 在此过程中, 所有含铅的原材料都被沉积到钙钛矿薄膜中, 含铅原材料的浪费和铅释放导致的污染都被显著降低. 这种方法制备的钙钛矿薄膜的性质可以由前驱体溶液的组分调节. CH3NH3Cl (MACl)可以调节结晶过程, 有助于提高薄膜表面覆盖率. CH(NH2)2I (FAI)有助于提高钙钛矿薄膜的热稳定性. 当前驱体组分为PbI2·(1−x)FAI·xMACl, x=0.75时, 快速成膜工艺制备的钙钛矿膜达到最优化性质, 由此制备的平面结太阳电池可以实现超过15%的能量转换效率, 迟滞现象很小, 并且重复性良好.

Applications of cesium in the perovskite solar cells

Perovskite solar cells have experienced an unprecedented rapid development in the power conversion efficiency (PCE) during the past 7 years, and the record PCE has been already comparable to the traditional polycrystalline silicon solar cells. Presently, it is more urgent to address the challenge on device stability for the future commercial application. Recently, the inorganic cesium lead halide perovskite has been intensively studied as one of the alternative candidates to improve device stability through controlling the phase transition. The cesium (Cs)-doped perovskites show more superior stability comparing with organic methylammonium (MA) lead halide perovskite or formamidinium (FA) lead halide perovskite. Here, recent progress of the inorganic cesium application in organic-inorganic perovskite solar cells (PSCs) is highlighted from the viewpoints of the device efficiency and the device stability.

Diboron-Assisted Interfacial Defect Control Strategy for Highly Efficient Planar Perovskite Solar Cells

Metal halide perovskite films are endowed with the nature of ions and polycrystallinity. Formamidinium iodide (FAI)-based perovskite films, which include large cations (FA) incorporated into the crystal lattice, are most likely to induce local defects due to the presence of the unreacted FAI species. Here, a diboron-assisted strategy is demonstrated to control the defects induced by the unreacted FAI both inside the grain boundaries and at the surface regions. The diboron compound (C12 H10 B2 O4 ) can selectively react with unreacted FAI, leading to reduced defect densities. Nonradiative recombination between a perovskite film and a hole-extraction layer is mitigated considerably after the introduction of the proposed approach and charge-carrier extraction is improved as well. A champion power conversion efficiency of 21.11% is therefore obtained with a stabilized power output of 20.83% at the maximum power point for planar perovskite solar cells. The optimized device also delivers negligible hysteresis effect under various scanning conditions. This approach paves a new way for mitigating defects and improving device performance.