Perovskite solar cells (PSCs) have made incredibly fast progress in past years, pushing the efficiency approaching 26%, which is comparable to the best silicon solar cells. One of the features...

Having demonstrated incredibly fast progress in power conversion efficiency, rising to a level comparable with that of crystalline silicon cells, lead‐based organic–inorganic hybrid perovskite solar cells are now facing the stability tests needed for industrialization. Poor thermal stability (<150 °C) owing to organic constituents and interlayer diffusion of materials (dopants), and environmental incompatibility due to Pb has surged the development of organic‐free, Pb‐free perovskites and dopant‐free hole transport materials (HTMs). The recent rapid increase in efficiency of cells based on inorganic perovskites, crossing 18%, demonstrates the great potential of inorganic perovskites as thermally stable and high‐efficiency cells. Although all kinds of Pb‐free perovskites lag in efficiency in comparison to the hybrid and inorganic perovskites, they also demonstrate better structural and environmental stability. The performance of dopant‐free HTMs matching/surpassing dopant‐containing HTMs makes the former a better choice for stability. Even though the efforts to enhance the stability of Pb‐based hybrid perovskites should continue by different techniques, organic‐free and lead‐free perovskites, and dopant‐free HTMs must be pursued with greater interest for the future. This review describes the present issues and possible strategies to address them, and thus will help to improve the overall performance of robust organic‐free, Pb‐free, and dopant‐free perovskite solar cells.

CsPbI2Br perovskite solar cells have attracted much attention because of the rapid development in their efficiency and their great potential as a top cell of tandem solar cells. However, the V OC outputs observed so far in most cases are far from that desired for a top cell. Up to now, with various kinds of treatments, the reported champion V OC is only 1.32 V, with a V OC deficit of 0.60 V. In this work, we found that aging of the SnCl2 precursor solution for the electron-transporting layer can promote the V OC of CsPbI2Br solar cells by employing a dopant-free-polymer hole transport material (HTM) over 1.40 V and efficiency over 15.5% with high reproducibility. With the champion V OC of 1.43 V, the V OC deficit was reduced to <0.50 V, which is achieved for the first time. This simple technique of SnCl2 solution aging forms a uniform and smooth amorphous SnO x film with pure Sn4+, elevates the conduction band of SnO x , and reduces the interfacial gaps and the trap state density of the device, resulting in enhancement in average V OC from ∼1.2 V in the nonaged case to ∼1.4 V in the aged case. Furthermore, the device using an aged SnCl2 solution also exhibits a much better long-term stability than that made of the fresh solution. These achievements in dopant/additive-free CsPbI2Br solar cells can be useful for future research on CsPbI2Br and tandem solar cells.

Lead halide perovskite single layers with three grain sizes are subjected to proton-beam irradiation in order to assess the durability and radiation tolerance of perovskite solar cells (PSCs) against space radiation. Proton-beam irradiation is chosen because proton beams significantly affect solar cell performance in the space environment. We evaluate the effects of proton beams by focusing on the grain structure, crystal structure, and carrier lifetime of a perovskite single layer by using scanning electron microscopy, X-ray diffraction, photoluminescence (PL) spectra, and time-resolved PL (TRPL). The results show that proton irradiation does not significantly affect the grain structure and crystal structure of perovskite layer; the TRPL results show that the carrier lifetime inside the grain is constant up to a fluence of 1 × 10 14 p + /cm 2 and decreases significantly at a fluence of 1 × 10 15 p + /cm 2 . Proton-beam radiation tolerance of the grain inside the perovskite layer is dominant in the radiation tolerance of PSCs.

Interfacial engineering, grain boundary, and surface passivation in organic–inorganic hybrid perovskite solar cells (HyPSCs) are effective in achieving high performance and enhanced durability. Organic additives and inorganic doping are generally used to chemically modify the surface contacting charge transport layers, and/or grain boundaries so as to reduce the defect density. Here, a simple but tricky one‐step method to dope organic–inorganic hybrid perovskite with Ge for the first time is reported. Unlike Ge doping to all‐inorganic perovskites, application of GeI2 in organic–inorganic perovskite precursors is challenging due to the extremely poor solubility of GeI2 in hybrid perovskite ink, leading to failure in the formation of uniform films. However, it is found that addition of methylammonium chloride (MACl) into the precursor remarkably increases the solubility of GeI2. This MACl‐assisted Ge doping of hybrid perovskites produces high‐quality crystalline film with its surface passivated with nonvolatile GeI2 (GeO2) and the volatile MACl additive also improves the uniformity of GeO2 distribution in the perovskite films. The resulting Ge‐doped mixed cation and mixed halide perovskite films with composition FA0.83MA0.17Ge0.03Pb0.97(I0.9Br0.1)3 show superior photoluminescence lifetime, power conversion efficiency above 22%, and greater stability toward illumination and humidity, outperforming photovoltaic properties of HyPSCs prepared without the Ge doping.