Prof Henry Snaith FRS

Abstract:

Utilizing molecular bridges presents a promising means to enhance the performance of perovskite solar cells (PSCs). However, concurrently bridging the perovskite absorber and its two adjacent interfaces remains a significant challenge that is yet to be achieved. Here, we construct dual molecular bridges at perovskite heterointerfaces, enabled by a self-organizing additive of 4-fluoro-phenethylammonium formate (4-F-PEAFa) and a synthesized hole transporter of [2-(7H-dibenzo[c, g]carbazol-7-yl)ethyl]phosphonic acid (DBZ-2PACz). The molecular bridges spanning two interfaces lead to the formation of an ‘integral carrier transport pathway’, mitigating both non-radiative recombination and charge-transport losses in the fabricated PSC devices. We thus achieve a champion power conversion efficiency (PCE) of 26.0% (25.6% certified) in inverted PSCs, accompanied by an exceptionally high fill factor of 0.87 (maximum 0.88 from the certified devices, 97% of its Shockley–Queisser limit) and a low ideality factor of 1.06. The unencapsulated devices retain 96% of their PCEs after aging at 85°C for 2200 h and 90% after maximum power point tracking at an elevated temperature of 50°C for 973 h.

Abstract:

Perovskite solar cells achieve high power conversion efficiencies but usually rely on vacuum-deposited metallic contacts, leading to high material costs for noble metals and stability issues for more reactive metals. Carbon-based materials offer a cost-effective and potentially more stable alternative. The vast majority of carbon-electrode PSCs use the negative-intrinsic-positive (n-i-p) or “hole-transport-layer-free” architectures. Here, we present a systematic study to assess the compatibility of “inverted”, p-i-n configuration PSC contact layers with carbon top electrodes. We identify incompatibilities between common electron transport layers and the carbon electrode deposition process and previously unobserved semiconducting properties in carbon electrodes with unique implications for charge extraction and electronic behavior. To overcome these issues, we introduce a double-layer atomic layer deposited tin oxide (SnO2) and Poly­(2,3-dihydrothieno-1,4-dioxin)-poly­(styrenesulfonate) (PEDOT:PSS), yielding up to 16.1% PCE and a retained 94% performance after 500 h of outdoor aging. The study is a crucial step forward for printable, metal-electrode-free, and evaporation-free perovskite PV technologies.

Abstract:

Interfacial materials tend to alter the crystallization, films growth and defect formation process of the as‐deposited perovskites, which has been a critical and fundamental factor in determining the efficiency and operational stability of perovskite‐based optoelectronic devices. This review explores the underlying mechanism of interfacial reactions, which can either result in degradations or be beneficial. The influence of interfacial reactions, mainly interface‐induced deprotonation of organic cations and amidation processes, are discussed in relation to their impact on perovskite film growth and ensuing optoelectronic device performance. It is further proposed strategies to regulate these reactions and mitigate their negative effects to achieve high performance optoelectronic devices.