以熱鑄法製備鈣鈦礦上電池並應用於矽晶串疊型太陽能電池

Abstract

近幾年，鈣鈦礦太陽能電池備受矚目是因為鈣鈦礦有下列優點:低製程成本、能隙可調性和高光電轉換效率。然而對於鈣鈦礦元件的製備，常見的製程往往是需要在惰性氣體的環境中的手套箱內製作，這會使其製備的成本增加，同時也會讓製備的複雜度提升，透過熱鑄製程，鈣鈦礦前驅物相轉變成鈣鈦礦所需的時間只需幾秒鐘，如此，前驅物受到外在氣氛的影響時間大幅縮短。因此，熱鑄製程比起一般製程更有機會使鈣鈦礦太陽能電池由實驗室規模進入到量產規模。此外，為突破單電池的效率極限(蕭基-奎伊瑟極限)並進一步提升電池效率，串疊型太陽能電池逐漸受到矚目。根據理論模擬與計算，高能隙鈣鈦礦上電池(能隙~1.72 eV)串疊矽晶太陽能電池可以得到高於40%的理論效率。 為了解鈣鈦礦電池在串疊太陽能電池的實際情況，本研究製備高能隙(~1.72 eV)以及低能隙(~1.55 eV)鈣鈦礦電池，用以作為四點式串疊電池的上電池，並討論不同能隙上電池串疊的結果。為了進一步提升上電池之效率進而串疊出更優異的電池效率，膠體工程與介面處理率先被引入，藉由加入1 v.%的甲醯胺，減少鈣鈦礦前驅溶液中鉛碘錯合物數量；以及氯化鎳後處理改善氧化鎳電子傳輸層的批覆率(由91.15%提升至97.05%)後，低能隙之電池的效率可由平均16.14%提升至17.04%；而高能隙電池效率亦可由平均13.89%提升至15.18%。基於上述的實驗結果，將上述兩種能隙之鈣鈦礦電池與矽晶太陽能電池串疊，其中高能隙鈣鈦礦效率平均可達18.55%(最高20.11%)，而低能隙之鈣鈦礦則可達平均20.26%(最高21.41%)。 在此研究的最後，我們也將我們低能隙鈣鈦礦電池的每層移至乾空氣下(~10 RH%)製備，對於銀電極元件，其平均效率下降到14.90%，而其與矽晶太陽能電池串疊後其效率平均為16.60%。於乾空氣中所製備的鈣鈦礦太陽能電池，效率的衰退主要是填充因子下降至71.46%所致，而填充因子的下降可歸咎於親水的功函數修飾層於含有水氣的環境中製備所致，因調整功函數的能力下降進而使得鈣鈦礦整體元件效率下降。

Recently, perovskite solar cells (PSCs) have attracted lots of attention due to its advantages of low processing cost, tunable bandgap (Eg) and high power conversion efficiency (PCE). However, for most of the solution process of perovskite layers, inert atmosphere is still required. By applying novel hot casting, perovskite is allowed to be fabricated in dry air since the formation of perovskite phase only takes few seconds that the influence of the atmosphere can be ignored. Therefore, hot casting brings a step closer to the commercialization of PSCs. On the other way, to break through the limit of monolithic cell and further the power conversion efficiency (PCE), establishing tandem solar cell is one of the feasible path to overcome Shockley–Queisser limit. Theoretically, wide Eg perovskite (Eg~1.72 eV) fits the requirement of the top cell when being tandem with Si bottom cell to bring out the highest prospective PCE of perovskite/silicon tandem solar cell (TSC). Here in this work, the wide Eg (~1.72 eV) and narrow Eg (~1.55 eV) perovskite solar cell have been fabricated via hot casting for four-terminal silicon tandem solar cell. To further the PCE of hot casted top PSCs, colloid engineering and NiOx/perovskite interface modification were adopted. With 1 v.% formamide in the precursor solution, the undesired lead polyhalide colloid in precursor solution can be reduced. Moreover, the coverage of NiOx hole transport layer can be improved from 91.15% to 97.05% via NiCl2 post treatment, avoiding the leakage flow of carrier from perovskite to FTO. By combining the colloid engineering and interface modification, large grain size of perovskite with 1 v.% formamide additive and minor current leakage from NiOx/perovskite interface, the PCE of PSC has been improved. For narrow Eg PSC, the PCE is increased from 16.14% to 17.04% and for wide Eg PSC, the PCE is increased from 13.89% to 15.18%. Based on the above results, the 4T narrow Eg and wide Eg perovskite/Si TSCs are demonstrated in this work. The former exhibits an average PCE of 20.26% (21.41% for champion device) and the latter has an average PCE of 18.55% (20.11% for champion device). Then we demonstrate that all layers of narrow Eg PSC and TSC can be fabricated in dry air (~10 RH%). The average PCE of 14.90% can be attained for opaque electrode and 16.60% for TSC. The decrease of PCE loss of all layer fabricated in dry air PSC can be ascribed to the hydrophilic work function modifier which is susceptible to the small amount of moisture in dry air, and therefore deteriorated the fill factor as well as PCE of PSC.