Ajay Kumar Jena

Surface defects and interfacial recombination losses often limit the performance of silver bismuth sulfide (AgBiS2) solar cells. Herein, we present a simple ultraviolet–ozone (UVO3) and subsequent water treatment (UVO3_water) strategy for surface engineering of solution-crystallized AgBiS2 thin films for improved solar cell efficiency without modifying the bulk crystal structure. Our results reveal that the UVO3 treatment removes residual organic impurities, induces surface oxygen-containing species possibly associated with S–O bonding, and subsequent water treatment (UVO3_water) promotes the formation of a Bi–O-rich surface (relative amount of 27%) on the surface of AgBiS2. This surface modification improves charge collection at the AgBiS2/poly(3-hexylthiophene-2,5 diyl, P3HT) interface and suppresses trap-assisted recombination. As a result, the optimized UVO3_water-treated solar cell achieves a power conversion efficiency (PCE) of 6.3%, with an exceptional short-circuit current density (Jsc) exceeding 39 mA cm–2, significantly higher than the previously reported value of 29.15 mA cm–2, and simultaneous improvement of open-circuit voltage (Voc) and fill factor (FF). Additionally, unencapsulated AgBiS2 solar cells exhibit good operational stability under continuous 1 Sun illumination, with efficiency increasing to 6.8%.

In response to the toxic heavy metal absorbers in perovskite solar cells (PSCs), this work focuses on the development of an environmentally friendly simple solution‐processed infrared (IR) absorber. In this work, a simple solution‐crystallized IR‐absorbing AgBiS₂ film is reported by spin‐coating silver, bismuth nitrates, and thiourea dissolved in dimethylformamide (DMF) to produce thick AgBiS₂ film. Extensive optimization of the precursor concentrations thicknesses and conductive substrates used allow for obtaining 250 nm AgBiS₂ film with different crystal sizes. When applied as an absorber in solar cells, solution‐crystalized AgBiS₂ thick film delivers an extraordinarily high current density of over 31 mA cm⁻². The devices show high stability under continuous 100 mW cm⁻² illumination and when stored in the dark for more than six months. When the AgBiS₂ layer is fabricated in a gradient fashion combining one layer of 0.25 m and three layers of 0.5 m precursor concentrations, the efficiency of 5.15% is registered which is the highest reported for the simple solution‐crystallized AgBiS₂ films.

Technological development is increasingly driven by environmental sustainability, with labels like ‘green’ gaining traction.

Perovskite solar cells (PSCs) have made incredibly fast progress in the past years, with the efficiency approaching 26%, which is comparable to those of the best silicon solar cells. One of the features of PSCs that make them stand out among all photovoltaics (PVs) is their high open-circuit voltage (V_OC) although they are made by solution processes. Compared to other solution-processed PVs such as organic photovoltaics and dye-sensitized solar cells, and vacuum-processed PVs like CdTe and CIGS, the loss in V_OC caused by non-radiative recombination in the case of PSCs is considerably low, which is even as low as that observed for vacuum-processed Si. The defect-tolerant nature of perovskites helps in preventing non-radiative recombination and therefore yields high V_OC in PSCs. By comparing the achieved performance with the Shockley–Queisser (S–Q) limits, it can be determined that while the photocurrent of PSCs reaches almost the theoretical limit, there is still room to improve the V_OC, especially in the case of all-inorganic and tin-based perovskites. Hence, improving the V_OC becomes critical for promoting device efficiency further. In this review paper, we focus our discussion on the recent development of V_OC of PSCs by beginning with a theoretical review highlighting the critical role of V_OC enhancement and the necessity of non-radiative recombination suppression for device performance improvement. As the recombination both in the bulk of the perovskite and on the surface/interfaces with charge transport layers is important, different methods depending on the perovskite composition and the nature of the electron transport layer (ETL) and hole transport material (HTM) have been developed to minimize recombination in the perovskite and at the interfaces. We provide a comprehensive review of different reported strategies for reducing undesirable recombination in the perovskite film and at the interfaces, by dividing our discussion into four parts based on the light absorbers used: organic–inorganic hybrid perovskites, all-inorganic perovskites, tin-based perovskites, and bismuth-based perovskites (analogs). Finally, a summary with an outlook on how reducing perovskite film defects and developing more suitable charge transport layers can further promote the V_OC and expand the practical application prospects of PSCs is presented.

The black γ‐phase of CsPbI₃ with its bandgap at ≈1.75 eV can enable the take‐off of tandem solar cells as soon as intrinsic instability to the yellow δ‐phase is solved. Here, a black γ‐phase is formed at low temperature (80–90 °C) by incorporating Eu through EuCl₃ or EuI₂. It is forced to become yellow by thermal heating under nitrogen. It is demonstrated how spectroscopic ellipsometry and the related critical points analysis provide a new diagnostic tool to monitor the transformation through the bandgap footprint. As two sides of the same coin, the consumption of the black γ‐phase and the growth of the yellow δ‐phase are addressed and modeled in the range of 60–100 °C using the Avrami's theory. This approach allows extracting the activation energies of the phase transformation that are 0.95 eV versus 1.15 eV using EuI₂ and EuCl₃, respectively. In situ transmission electron microscopy analyses combined with fast marching simulations highlight that the phase transformation occurs through constant nucleation and growth. Europium has indeed the capability to tackle those processes and to extend the durability of the black γ‐phase at 30 °C in N₂ to ≈250 days, hugely above the one observed without Eu (≈hours).

The control of evaporation kinetics depends on perovskite compositions.